Engine Controls - System & Component Testing: Diagnosis

Diagnostic Procedures

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Install a scan tool. Turn ON the ignition, with the engine OFF. With the scan tool observe the MAP sensor pressure. Compare this value to a value observed in a known good vehicle. Is the difference between the two vehicles less than 3 kPa? If yes, go to next step. If no, go to step 7 .
Observe the MAP sensor pressure on the scan tool. Start the engine. Does the MAP sensor value change? If yes, go to next step. If no, go to step 7 .
Turn OFF the ignition. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness. Connect a Vacuum Pump (J 23738-A) to MAP sensor. Turn ON the ignition, with the engine OFF. Observe the MAP sensor pressure as you SLOWLY apply vacuum 1 in. Hg at a time. Each one inch of vacuum should result in a 3 to 4 kPa drop in the MAP sensor pressure. Does the scan tool indicate that the MAP sensor is operating normally? If yes, go to next step. If no, go to step 15 .
Observe the MAP sensor pressure on the scan tool with 20 in. Hg of vacuum applied to the sensor. Is the pressure less than 34 kPa? If yes, go to next step. If no, go to step 7 .
Disconnect the MAP sensor from the J 23738-A. The MAP sensor pressure should return to the value observed in step 2 . Does the MAP sensor pressure return to the value observed earlier? If yes, system is okay. If no, go to step 15 .
Turn OFF the ignition. Disconnect the MAP sensor from the engine harness. Turn ON the ignition, with the engine OFF. Observe the MAP sensor VOLTAGE display on the scan tool. Is the voltage more than 0.1 V? If yes, go to step 11 . If no, go to next step.
Connect a test light to a good ground. Probe the 5-volt reference circuit of the MAP sensor with the test light. Perform a voltage drop test across the test light with a DVOM. Does the voltage measure more than 4.4 V? If yes, go to next step. If no, go to step 12 .
Jumper the MAP sensor 5-volt reference circuit to the MAP sensor signal circuit using a fused jumper wire. Does the scan tool indicate that the MAP sensor voltage is near 5 V? If yes, go to next step. If no, go to step 13 .
Remove the jumper. Disconnect the electrical connector of the Engine Coolant Temperature (ECT) sensor. Probe the MAP sensor low reference circuit with a test light connected to battery positive voltage. Does the test light illuminate? If yes, go to step 15 . If no, go to step 14 .
Test the signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
Test the 5-volt reference circuit of the MAP sensor for high resistance or an open. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
Test the signal circuit for the following conditions: High resistance. An open. A short to ground. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
Test the MAP sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
Inspect the MAP sensor connector for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
Replace the MAP sensor. After repairs, go to step 19 .
Inspect the PCM for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
Use the scan tool in order to clear the DTCs that may have set. Turn OFF the ignition for 30 seconds. Start the engine. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Diagnostic Aids

Inspect for the following conditions

Restrictions in the MAP sensor vacuum source.
MAP sensor seal missing or damaged.
Vacuum hoses disconnected, damaged, or incorrectly routed.
Intake manifold vacuum leaks.
Vacuum leaks at the throttle body.
Vacuum leaks at the Exhaust Gas Recirculation (EGR) valve flange and pipes.

Diagnostic Procedure

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Select scan tool DTC display function for Alternative Fuels Engine Control Module (AF ECM). Does scan tool display DTC P1650? If yes, go to DTC P1650 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits. If no, go to next step.
Turn ON the ignition with the engine OFF. With scan tool in Alternative Fuels - Special Function menu, command Fuel Pump ON. Listen for audible fuel pump operation. Can you hear fuel pump operate as commanded? If yes, go to next step. If no, go to step 5 .
Start and idle engine on CNG. Probe fuel pump Prime terminal using Test Light (J 34142-B) connected to ground. Is test light illuminated? If yes, go to step 10 . If no, diagnose alternative fuel system. Go to «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
With scan tool in Alternative Fuels - Special Function menu, command Fuel Pump ON and OFF. Listen or feel for operation of Lock-Off Solenoid Relay. Does Lock-Off Solenoid Relay operate when fuel pump is commanded ON and OFF? If yes, go to next step. If no, diagnose fuel lock-off relay. Go to «FUEL LOCK-OFF RELAY»(ref-150429-S07542980042002111300000) .
With scan tool in Alternative Fuels - Special Function menu, command Fuel Pump ON and OFF. Listen or feel for operation of gasoline fuel pump relay. Does gasoline fuel pump relay operate when fuel pump is commanded ON and OFF? If yes, go to «FUEL PUMP RELAY (ALL EXCEPT 2.2L & 3.0L VUE, 3.4L, 5.0L & 5.7L)»(ref-150429-S39786676722002111300000) under FUEL SYSTEM (GASOLINE). If no, go to next step.
Disconnect AF fuel pump relay. Probe Fuel Pump Relay Control circuit terminal No. 30 with Test Light (J 34142-B) connected to ground. With scan tool in Alternative Fuels - Special Function menu, command Fuel Pump ON. Does test light illuminate when fuel pump is commanded ON? If yes, go to next step. If no, go to step 10 .
Connect AF fuel pump relay. Remove gasoline fuel pump relay. Probe gasoline fuel pump relay control terminal No. 85 using Test Light (J 34142-B) connected to ground. With scan tool in Alternative Fuels - Special Function menu, command Fuel Pump ON. Does test light illuminate when fuel pump is commanded ON? If yes, go to «FUEL PUMP RELAY (ALL EXCEPT 2.2L & 3.0L VUE, 3.4L, 5.0L & 5.7L)»(ref-150429-S39786676722002111300000) under FUEL SYSTEM (GASOLINE). If no, go to next step.
Test Fuel Pump Relay circuit between AF fuel pump relay and gasoline fuel pump relay for an open. See «WIRING DIAGRAMS»(ref-142952) article. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
Repair Fuel Pump Relay Control circuit between AF fuel pump relay terminal No. 30 and circuit splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 12 .
Replace AF Fuel Pump Relay. After repairs, go to next step.
Remove all test equipment except scan tool. Connect any disconnected components, fuses, etc. With scan tool, clear DTC information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe MIL. Observe vehicle performance and driveability. After operating vehicle inspect BOTH control modules for stored DTCs. Does vehicle operate on CNG with normal driveability, no MIL illumination and no stored DTCs? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)

Note. For component locations, see COMPONENT LOCATIONS .

Note. If DTC sets, causing gasoline operation, check pressure only before DTC sets. If vehicle will not idle on CNG, check cranking pressure. A rhythmic pressure fluctuation of 10-20 psi is normal.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. Are AF ECM DTCs P0201-P0208, P0602, P0605 or P1215 set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
Connect vehicle to filling station. Ensure fuel tank is at least 1/3 full. Fill CNG fuel tank if necessary. Observe Fuel Tank Pressure (FTP) sensor data display with scan tool. Does FTP sensor display a pressure at or above 1200 psi (8274 kPa)? If yes, go to next step. If no, go to step 6 .
Observe Fuel Rail Pressure (FRP) sensor display with scan tool. Observe FRP sensor display while cranking engine. If engine will not start on CNG, use pressure values observed during cranking. Is FRP sensor value within 40-50 psi (276-345 kPa)? If yes, go to next step. If no, go to step 9 . If engine starts on CNG, allow engine to idle until normal operating temperature is obtained. Observe and record FRP sensor display with scan tool. Compare recorded scan tool display pressure values to specification. Is FRP sensor value within 40-50 psi (276-345 kPa)? If yes, go to next step. If no, go to step 9 .
Turn ON the ignition with the engine OFF. Observe and record fuel rail pressure immediately after cranking engine for a few seconds. Turn engine OFF if it starts. Monitor fuel rail pressure for 5 minutes. Does fuel rail pressure drop more than 3 psi (21 kPa)? If yes, go to step 13 . If no, go to next step.
Turn OFF the ignition. Remove dust cap from pressure test port located on Intermediate Pressure Regulator (IPR). Depress valve core stem in order to relieve CNG fuel pressure from IPR. Using components available within CNG Electronic Pressure Gauge Kit (J 39970), install transducer to adapter with Fuel Test Port Adapter (J 39970-100) onto pressure test port. Connect (J 39970) to (J 39970-100). Connect DMM (J 39200) to (J 39970). Zero DMM (J 39200) using procedure included with (J 39970). Observe fuel pressure with DMM while cranking engine. If engine will not start on CNG, use pressure values observed during cranking. Are all fuel pressure values within 110-210 psi (758-1448 kPa)? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step 15 . If engine does start on CNG, allow engine to idle until normal operating temperature is obtained. NOTE: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless fluctuations become excessive. Observe and record pressure indicated by DMM at engine idle. Observe and record pressure indicated by DMM during engine load by performing following: Apply parking brake. Firmly apply and hold brake pedal. Place vehicle in forward gear. Observe pressure while depressing throttle to 75 percent or more for a maximum of 10 seconds. Allow engine to idle for a minimum of 2 minutes in order to cool transmission. Compare recorded pressure values to value range specified. Are all fuel pressure values within 110-210 psi (758-1448 kPa)? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step 15 .
Listen for High Pressure Lock-Off (HPL) solenoid operation as you quickly turn ignition between LOCK and RUN position. Can operation of HPL be heard? If yes, go to next step. If no, go to step 8 .
Remove fuel tank cover. Ensure manual tank valve is fully open by turning screw fully counterclockwise. Did you have to open manual tank valve? If yes, go to step 2 . If no, go to step 17 .
Remove fuel tank cover. Disconnect harness connector of HPL solenoid. Connect Test Light (J 34142-B) between body harness HPL connector terminals. Observe test light as you turn ON the ignition, with the engine OFF. Does test light illuminate for about 2 seconds? If yes, go to step 21 . If no, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits.
Turn OFF the ignition. Remove dust cap from pressure test port located on Intermediate Pressure Regulator (IPR). Depress valve core stem in order to relieve CNG fuel pressure from IPR. Using components available within CNG Electronic Pressure Gauge Kit (J 39970), install transducer to adapter with Fuel Test Port Adapter (J 39970-100) onto pressure test port. Connect (J 39970) to (J 39970-100). Connect DMM (J 39200) to (J 39970). Zero DMM (J 39200) using procedure included with (J 39970). Observe fuel pressure with DMM while cranking engine. If engine will not start on CNG, use pressure values observed during cranking. Is pressure value within 110-210 psi (758-1448 kPa)? If yes, go to step 11 . If no, go to next step. If engine does start on CNG, allow engine to idle until normal operating temperature is obtained. NOTE: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless fluctuations become excessive. Observe and record pressure indicated by DMM at engine idle. Compare recorded pressure value to specification. Is pressure value within 110-210 psi (758-1448 kPa)? If yes, go to step 11 . If no, go to next step.
Is fuel pressure greater than 210 psi (1448 kPa)? If yes, go to step 19 . If no, go to step 15 .
Turn OFF the ignition. Feel Low Pressure Lock-Off (LPL) solenoid as an assistant cranks engine. Can you feel LPL operate as engine is cranking? If yes, go to step 18 . If no, go to next step.
Turn OFF the ignition. Disconnect harness connector of LPL solenoid. Connect Test Light (J 34142-B) between engine harness LPL connector terminals. Observe test light as you crank engine. Does test light illuminate during cranking? If yes, go to step 20 . If no, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits.
Inspect for a fuel system leak between LPL solenoid and CNG fuel injectors. Replace any leaking components as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to next step.
Raise CNG fuel rails, lines and injectors as an assembly. Remove IGN E fuse. Crank engine for 5 seconds in order to charge CNG fuel rail with pressure. Locate and replace leaking CNG fuel injector. After repairs, go to step 22 .
Inspect fuel line between HPL and HPR and fuel line between HPR and LPL for kinks, bends, damage or obstruction. An obstructed fuel line may be cool or frosted near obstruction when fuel flows through line. Repair or replace components as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to next step.
Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S26369886172002110100000) under BASIC FUEL SYSTEM CHECKS (CNG) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. Replace CNG in-line filter. Replace HPR filter. Observe fuel pressure with DMM while cranking engine. If engine will not start on CNG, use pressure value observed during cranking. Is fuel pressure value within 110-210 psi (758-1448 kPa)? If yes, go to step 22 . If no, go to step 19 . If engine does start on CNG, allow engine to idle until normal operating temperature is obtained. NOTE: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless fluctuations become excessive. Observe and record pressure indicated by DMM at engine idle. Observe and record pressure indicated by DMM during engine load by performing following steps: Apply parking brake. Firmly depress and hold brake pedal. Place vehicle in forward gear. Observe pressure while depressing throttle to 75 percent or more for a maximum of 10 seconds. Allow engine to idle for a minimum of 2 minutes in order to cool transmission. Compare recorded pressure values to specification. Are all fuel pressure values within 110-210 psi (758-1448 kPa)? If yes, go to step 22 . If no, go to step 19 .
Replace Fuel Tank Pressure (FTP) sensor. After repairs, go to step 22 .
Replace Intermediate Pressure Regulator (IPR). After repairs, go to step 22 .
Replace High Pressure Regulator (HPR). After repairs, go to step 22 .
Replace Low Pressure Lock-Off (LPL) solenoid. After repairs, go to step 22 .
Replace High Pressure Lock-Off (HPL) solenoid. After repairs, go to step 22 .
Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S26369886172002110100000) under BASIC FUEL SYSTEM CHECKS (CNG) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. Turn OFF the ignition. Remove all remaining test equipment. Ensure dust cap is installed onto underhood test port. Start and idle engine. Inspect for CNG fuel system leaks between fuel tank and IPR using Ultrasonic Leak Detector (J 41416). Inspect for CNG fuel system leaks at fuel rails and injectors using Snoop® or soapy water. Repair any leaks as necessary. Using scan tool, clear DTC information from AF ECM and from PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe MIL. Observe vehicle performance and driveability. Does vehicle operate on CNG with normal driveability and no MIL illumination? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Disconnect lock-off solenoid relay connector. Connect Test Light (J 34142-B) between relay switch power supply circuit terminal No. 30 and a known good ground. Does test light illuminate? If yes, go to next step. If no, go to step 6 .
Connect Test Light (J 34142-B) between relay coil ground circuit terminal No. 86 and battery positive. Does test light illuminate? If yes, go to next step. If no, go to step 16 .
Connect Test Light (J 34142-B) between relay coil power circuit terminal No. 85 and a known good ground. Observe test light as you turn the ignition ON while leaving the engine OFF. Does test light briefly illuminate? If yes, go to next step. If no, go to step 8 .
Turn OFF the ignition. Connect lock-off solenoid relay connector. Backprobe lock-off solenoid relay switch output circuit terminal No. 87 with Test Light (J 34142-B) connected to a known good ground. Observe test light as you turn the ignition ON while leaving the engine OFF. Does test light briefly illuminate? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step 18 .
Inspect AFS 20-amp MaxiFuse®. Is fuse open? If yes, go to step 10 . If no, go to next step.
Test AFS MaxiFuse® circuit for an open condition between Fuse Block - Underhood connector terminal and lock-off solenoid relay connector terminal. Test underhood fuse block for proper operation. Inspect underhood fuse block connector terminal and lock-off solenoid relay connector terminal for proper contact. Inspect in-line connector terminal "E" for proper terminal contact. Repair wiring or terminal contact as necessary. After repairs, go to step 21 .
Turn OFF the ignition. Disconnect in-line connector C006. Connect Test Light (J 34142-B) between PCM harness fuel pump relay Control circuit terminal "E" and a known good ground. Observe test light as you turn ON the ignition leaving the engine OFF. Does test light briefly illuminate? If yes, go to step 15 . If no, go to next step.
Test for an open fuel pump relay Control circuit between gasoline PCM and in-line connector C006. See «WIRING DIAGRAMS»(ref-142952) article. Inspect PCM connector and in-line connector C006 for proper terminal contact. Repair wiring or terminals as necessary. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 20 .
Replace AFS 20-amp MaxiFuse®. Inspect AFS 20-amp MaxiFuse®. Did replacement fuse open? If yes, go to step 17 . If no, go to next step.
Turn the ignition OFF. Disconnect LPL connector. Remove fuel tank cover. Disconnect HPL connector. Connect Test Light (J 34142-B) between lock-off solenoid relay switch output circuit terminal No. 87 and battery positive. Is test light illuminated? If yes, go to step 19 . If no, go to next step.
With DMM (J 39200) measure and record resistance between High Pressure Lock-Off (HPL) solenoid connector terminals. Is HPL solenoid outside of 16.3-20.6 ohms? If yes, replace HPL solenoid. If no, go to next step.
With DMM (J 39200) measure and record resistance between Low Pressure Lock-Off (LPL) solenoid connector terminals. Is LPL solenoid outside of 6.2-10 ohms? If yes, replace LPL solenoid. If no, go to next step.
Replace AFS 20-amp MaxiFuse®. Connect HPL solenoid. Crank engine for 10 seconds. Inspect AFS 20-amp MaxiFuse®. Is fuse open? If yes, replace HPL solenoid. If no, replace LPL solenoid.
Test for an open circuit between lock-off relay coil power supply terminal No. 85 and in-line connector terminal "E". See «WIRING DIAGRAMS»(ref-142952) article. Test for a short to ground on lock-off relay coil power supply circuit. Repair wiring as necessary. After repairs, go to step 21 .
Repair open lock-off solenoid relay coil ground circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 21 .
Repair shorted lock-off solenoid relay switch power circuit between relay and fuse. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 21 .
Replace the lock-off relay. After repairs, go to step 21 .
Repair short to ground on lock-off solenoid relay switch output circuit between relay and LPL or HPL solenoid. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 21 .
Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
Remove all test equipment except scan tool. Connect any disconnected components, fuses, etc. Using scan tool, clear DTC information from AF ECM and PCM. Turn OFF the ignition and wait 30 seconds. Start engine and operate vehicle. Observe MIL. Observe vehicle's performance and driveability. After operating vehicle, inspect both control modules for stored DTCs. Does vehicle operate on CNG with normal driveability, no MIL illumination, and no stored DTCs? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

Circuit Description

The Alternative Fuels Engine Control Module (AF ECM) and Powertrain Control Module (PCM) are connected by Alternative Fuels Operation (AFO) signal circuit. In order for engine to start and operate on CNG, PCM must be commanded to disable gasoline fuel injectors, switch to a different ignition spark calibration and disable some PCM DTCs. AF ECM performs switch-over command by grounding AFO signal circuit when CNG operation is desired. Bi-fuel (KL6) equipped vehicles primary fuel source is CNG. The vehicle will only switch-over to gasoline operation if one of the following conditions is present

Fuel Tank Pressure (FTP) sensor indicates CNG tank has less than 200 psi (1379 kPa).
Fuel Rail Pressure (FRP) sensor indicates low CNG fuel rail pressure.
A system fault is detected by AF ECM.
Every 100th start, vehicle will start and run briefly on gasoline. After this, a switch-over to CNG will occur during first decel condition.
Engine cranks for 8 seconds and fails to start on CNG.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Crank or idle engine for 10 seconds. Observe Diagnostic Trouble Code (DTC) information from AF ECM with scan tool. Does scan tool display DTC P0201-P0208, P0602, P0605 or P1215 failed this ignition? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
Observe Fuel Indicator Lamp (FIL) while engine is running. Is FIL illuminated? If yes, go to step 5 . If no, go to next step.
Condition is intermittent. See «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. Is their a system operation concern? If yes, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. If no, system is okay.
With scan tool, communicate with AF ECM and observe AFO Signal and AFO Signal Command data displays. Observe displays as you crank and start engine. Do data displays indicate AF ECM is in control of engine fueling? If yes, go to «FUEL INDICATOR LAMP ALWAYS ON - ALTERNATIVE FUELS»(ref-150429-S14066628842002112100000) . If no, go to next step.
Do both displays indicate the same information? If yes, go to next step. If no, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article.
Turn OFF the ignition. Disconnect harness connector of a CNG fuel injector. Turn ON the ignition, with the engine OFF. Probe Ignition Feed circuit of CNG fuel injector with a test light connected to a known good ground. Does test light illuminate? If yes, go to next step. If no, go to «FUEL INJECTOR CIRCUIT DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S39032906222002112100000)
Verify CNG fuel tank is at full pressure by connecting vehicle to a CNG dispensing station and filling CNG fuel tank. Turn ON the ignition, with the engine OFF. Observe FTP scan tool data display. Is FTP sensor accurately indicating fuel pressure? If yes, go to next step. If no, go to «FUEL GAUGE INACCURATE OR INOPERATIVE - ALTERNATIVE FUELS»(ref-150429-S34376398282002111300000) .
Turn the ignition OFF and wait 15 seconds. Turn ON the ignition, with the engine OFF. With scan tool, communicate with AF ECM and observe Fuel Rail Pressure (FRP) sensor data display. Observe FRP data display while cranking engine. Does FRP data display ever indicate fuel pressure more than 40 psi (276 kPa)? If yes, go to next step. If no, go to «FUEL INJECTOR CIRCUIT DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S39032906222002112100000) .
Inspect ignition system for proper voltage output using Spark Tester (J 26792). Remove and inspect spark plugs for wet (fouled) plugs, cracks, excessive wear, incorrect gap, burned electrodes or heavy deposits. Inspect spark plug wires for damage. Spray secondary ignition with a water bottle, and check for crossfire or missing. Inspect AF ECM and PCM grounds for being clean, tight, and properly located. Repair as necessary. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
Replace AF ECM. After repairs, go to next step.
Connect any disconnected components, fuses, etc. With scan tool, clear DTC Information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe FIL and MIL. Observe vehicle performance and driveability. After operating vehicle, inspect AF ECM and PCM for stored DTCs. Does vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article, or see SYMPTOM DIAGNOSIS under SYMPTOMS (BI-FUEL & CNG) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

Fuel Indicator Light (FIL) informs driver what fuel engine is operating on. This vehicle utilizes a Powertrain Control Module (PCM) and an Alternative Fuels Engine Control Module (AF ECM) in order to control engine operation. AF ECM controls CNG engine operation and PCM controls gasoline engine operation. AF ECM and PCM are connected by AFO Signal circuit. AF ECM will command CNG engine operation by grounding AFO Signal circuit. PCM will turn OFF FIL whenever AFO Signal circuit is grounded. Instrument panel gauge fuse supplies positive voltage source for FIL. PCM supplies ground path.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Start and idle engine. Is Fuel Indicator Light (FIL) illuminated? If yes, go to next step. If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Observe operation of other Instrument Panel (IP) gauges and/or lights. Do all IP indicators, except FIL, operate correctly? If yes, go to next step. If no, perform Diagnostic System Check - Instrument Cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
With scan tool, communicate with AF ECM and observe AFO Signal and AFO Signal Command data parameters. Observe data parameters as you crank and start engine. Do both data parameters indicate AF ECM is in control of engine fueling? If yes, go to next step. If no, go to «FUEL SYSTEM UNWANTED SWITCH TO GASOLINE (BI-FUEL ONLY)»(ref-150429-S37033910182002111300000)
Turn OFF the ignition. Disconnect PCM connectors. Turn ON the ignition, with the engine OFF. Is fuel indicator light illuminated? If yes, go to next step. If no, go to step 7 .
Test FIL Control circuit between PCM connector terminal and IP for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 8 . If no, perform Diagnostic System Check - Instrument Cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
Remove all test equipment except scan tool. Connect any disconnected components, fuses, etc. With scan tool, clear DTC information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Observe FIL. Start engine and operate vehicle. Does FIL operate for a 2 second bulb check and then turn OFF? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

FUEL INJECTOR CIRCUIT DIAGNOSIS (BI-FUEL & CNG)

Note. For component locations, see COMPONENT LOCATIONS .

Alternative Fuels Engine Control Module (AF ECM) enables appropriate fuel injector on intake stroke for each cylinder. Each bank of fuel injectors has a fuel injector relay. Battery voltage is supplied directly to switch side of fuel injector relays. An ignition voltage is supplied to coil side of fuel injector relays. AF ECM controls each fuel injector by grounding Control circuit via a solid state device called a driver.

Performing Fuel Injector Coil Test may help isolate an intermittent condition. See «FUEL INJECTOR COIL TEST (BI-FUEL & CNG)»(ref-150429-S04012823702002112100000) .
For an intermittent condition, see «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
With scan tool, observe Alternative Fuels Engine Control Module (AF ECM) Diagnostic Trouble Code (DTC) information. Are DTCs P0201-P0208, or DTC P1650 set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
Crank engine for 4 seconds. Does engine start and idle on all cylinders? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S41200243412002112100000) . If no, go to next step.
Inspect IGN E fuse. Is IGN E fuse open? If yes, go to next step. If no, go to step 9 .
Turn OFF the ignition. Disconnect both fuel injector relays. Disconnect alternative fuels fuel pump relay. Disconnect AF ECM harness connector C001. Probe ignition voltage circuit of fuel injector relays, at under hood bussed electrical center, with a test light connected to battery voltage. Is test light illuminated? If yes, go to step 17 . If no, go to next step.
Install a NEW IGN E fuse. Turn ON the ignition, with the engine OFF. Install fuel injector relays one at a time. Inspect IGN E fuse after each relay is installed. Does fuse open after either relay is installed? If yes, go to step 22 . If no, go to next step.
Install AF fuel pump relay. Inspect IGN E fuse. Is fuse open? If yes, go to step 23 . If no, go to next step.
Turn OFF the ignition. Install AF ECM harness connector C001. Turn ON the ignition, with the engine OFF. Inspect IGN E fuse. Is fuse open? If yes, go to step 24 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S41200243412002112100000) .
Turn OFF the ignition. Disconnect both fuel injector relays. Turn ON the ignition, with the engine OFF. Probe ignition voltage circuit of both fuel injector relays with a test light connected to a known good ground. Does test light illuminate for both circuits? If yes, go to next step. If no, go to step 16 .
Probe battery voltage circuit of both fuel injector relays with a test light connected to a known good ground. Does test light illuminate for both circuits? If yes, go to step 13 . If no, go to next step.
Probe battery voltage circuit of circuit that did not illuminate test light with a test light connected to battery voltage. Does test light illuminate? If yes, go to step 18 . If no, go to next step.
Probe battery voltage circuit of fuel injectors at fuel injector relay, with a test light connected to battery voltage. Does test light illuminate? If yes, go to step 19 . If no, go to step 21 .
Probe ground circuit of both fuel injector relays with a test light connected to battery voltage. Does test light illuminate for both circuits? If yes, go to next step. If no, go to step 20 .
Turn OFF the ignition. Install both fuel injector relays. Disconnect a harness connector of a fuel injector from each bank of engine. Turn ON the ignition, with the engine OFF. Probe battery voltage circuit of fuel injectors with a test light connected to a known good ground. Does test light illuminate for both circuits? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S41200243412002112100000) . If no, go to next step.
Inspect for proper terminal contact at harness connector of appropriate fuel injector relay. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 22 .
Repair ignition voltage circuit of fuel injector relays for an open. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Repair ignition voltage circuit of fuel injector relays for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Repair short to ground in battery voltage circuit of fuel injector relay. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Repair short to ground in battery voltage circuit between fuel injector relay and fuel injectors. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Repair ground circuit of fuel injector relays for an open. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Repair battery voltage circuit of fuel injector relays for an open. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Replace appropriate fuel injector relay. After repairs, go to step 25 .
Replace AF fuel pump relay. After repairs, go to step 25 .
Replace AF ECM. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

FUEL INJECTOR COIL TEST (BI-FUEL & CNG)

Note. For component locations, see COMPONENT LOCATIONS .

Alternative Fuels Engine Control Module (AF ECM) enables appropriate CNG fuel injector on intake stroke for each cylinder. A voltage is supplied to CNG fuel injectors through a pair of fuel injector relays. AF ECM controls each fuel injector by grounding Control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high, or low, will affect engine driveability. A Fuel Injector Control circuit DTC may not set, but a misfire may be apparent. Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Measure resistance of each CNG fuel injector with a DMM. Do any fuel injectors display a resistance outside 1-2 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S14378043682002112100000) .
Measure resistance of each CNG fuel injector with DMM. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 0.5 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S14378043682002112100000) . If no, go to next step.
Add all CNG fuel injector resistance values together to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace CNG fuel injector that displays greatest resistance difference, above or below the average. After repairs, go to step 7 .
Replace fuel injector or fuel injectors that are out of specified range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(ref-150429-S19147838712002112100000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-150429-S22193937432002112100000) .

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL

Note. For component locations, see COMPONENT LOCATIONS .

The Fuel Injector Tester (J 39021) energizes CNG fuel injector for a precise amount of time allowing a measured amount of fuel into manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each fuel injector.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Did you perform Fuel Injector Coil Test? If yes, go to next step. If no, go to «FUEL INJECTOR COIL TEST (BI-FUEL & CNG)»(ref-150429-S04012823702002112100000) .
Start and idle engine. Observe Fuel Rail Pressure (FRP) sensor parameter with scan tool. Is fuel pressure within 40-50 psi (275-345 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
Turn OFF the ignition. Turn ON the ignition, with the engine OFF. Monitor Fuel Rail Pressure (FRP) sensor parameter with scan tool. Does fuel rail pressure remain constant? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
Turn OFF the ignition. Connect Fuel Injector Tester (J 39021) to a fuel injector. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Turn ON the ignition, with the engine OFF. Record fuel pressure indicated by FRP sensor after fuel pressure stabilizes. This is first pressure reading. Energize CNG fuel injector by depressing "Push To Start Test" button on fuel injector tester. Record fuel pressure indicated by FRP sensor. This is second fuel pressure reading. Repeat for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. The result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 2.0 psi (14 kPa)? If yes, go to next step. If no, go to SYMPTOM DIAGNOSIS under SYMPTOMS (BI-FUEL & CNG) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected CNG fuel injector. After repairs, go to next step.
Operate vehicle in order to verify repair. Does a driveability condition still exist? If yes, go to SYMPTOM DIAGNOSIS under SYMPTOMS (BI-FUEL & CNG) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH TECH 2

Note. For component locations, see COMPONENT LOCATIONS .

The scan tool first energizes High Pressure Lock-Off (HPL) solenoid, Low Pressure Lock-Off (LPL) solenoid and CNG fuel injectors for a precise amount of time allowing a measured amount of fuel into manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each fuel injector.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Did you perform Fuel Injector Coil Test? If yes, go to next step. If no, go to «FUEL INJECTOR COIL TEST (BI-FUEL & CNG)»(ref-150429-S04012823702002112100000) .
Start and idle engine. Observe Fuel Rail Pressure (FRP) sensor parameter with scan tool. Is fuel pressure within 40-50 psi (275-345 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
Turn OFF the ignition. Turn ON the ignition, with the engine OFF. Monitor Fuel Rail Pressure (FRP) sensor parameter with scan tool. Does fuel rail pressure remain constant? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure sensor after fuel rail pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by FRP sensor after fuel injector has stopped pulsing. This is second fuel pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. The result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 2.0 psi (14 kPa)? If yes, go to next step. If no, go to SYMPTOM DIAGNOSIS under SYMPTOMS (BI-FUEL & CNG) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected CNG fuel injector. After repairs, go to next step.
Operate vehicle in order to verify repair. Does a driveability condition still exist? If yes, go to SYMPTOM DIAGNOSIS under SYMPTOMS (BI-FUEL & CNG) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

The CNG fuel gauge system consists of the Fuel Tank Pressure (FTP) sensor, Fuel Tank Temperature (FTT) sensor, Pulse Width Modulated (PWM) output circuit, dash mounted fuel gauge and dash mounted fuel gauge select switch (Bi-fuel/KL6 only). Alternative Fuels Engine Control Module (AF ECM) monitors fuel pressure and fuel temperature in CNG fuel tank. Volume of CNG varies with pressure and temperature. In order to display an accurate fuel gauge reading, AF ECM will perform a calculation based upon fuel pressure and temperature and determine correct amount of fuel remaining in fuel tank. AF ECM converts calculated fuel level into a PWM signal that is monitored by PCM. PCM sends fuel level information to instrument panel fuel gauge via Class 2 serial data circuit. Vehicles that are equipped with Bi-fuel (KL6) option also utilize a fuel gauge select switch. Fuel gauge select switch is monitored by PCM. When switch is pressed, PCM will display fuel level for non-operating fuel system, for about 10 seconds.

Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Is customers concern a normal operating condition? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to next step.
Turn ON the ignition, with the engine OFF. Observe Alternative Fuel Level data display from AF ECM with scan tool. Observe Instrument Panel (IP) fuel gauge. Does IP fuel gauge accurately display Alternative Fuel Level? If yes, go to step 10 . If no, go to next step.
With scan tool, communicate with AF ECM and observe AFO Signal and AFO Signal Command data parameters. Observe data parameters as you crank and start engine. Do both data parameters indicate AF ECM is in control of engine fueling? If yes, go to next step. If no, go to «FUEL SYSTEM UNWANTED SWITCH TO GASOLINE (BI-FUEL ONLY)»(ref-150429-S37033910182002111300000) .
With scan tool, communicate with IP. Command fuel gauge between Full and Empty. Does fuel gauge operate as commanded? If yes, go to next step. If no, perform DIAGNOSTIC SYSTEM CHECK - INSTRUMENT CLUSTER in appropriate ANALOG INSTRUMENT PANEL article.
Is this vehicle equipped with Bi-fuel (KL6) option? If yes, go to next step. If no, go to step 15 .
Turn ON the ignition, with the engine OFF. Observe Fuel Gauge Selected data display from PCM with scan tool. Press fuel gauge select switch. Does Fuel Gauge Selected data display change when switch is Pressed? If yes, go to step 15 . If no, go to next step.
Turn OFF the ignition. Disconnect PCM connectors. Turn ON the ignition, with the engine OFF. Probe Fuel Gauge Select Switch Signal circuit with a test light connected to battery voltage. Is test light illuminated? If yes, go to step 17 . If no, go to next step.
Press fuel gauge select switch while observing test light. Does test light illuminate when switch is pressed? If yes, go to step 23 . If no, go to step 18 .
Observe Fuel Temperature Sensor voltage display. Does display indicate a voltage more than 4.8 volts? If yes, go to step 20 . If no, go to next step.
Observe Fuel Tank Pressure Sensor voltage display. Does display indicate a voltage more than 4.8 volts? If yes, go to step 21 . If no, go to next step.
Observe Fuel Temperature Sensor and IAT Sensor data displays with scan tool. Compare temperature displays. Does each sensor indicate the same temperature plus or minus 35°F (20°C)? If yes, go to next step. If no, go to step 25 .
Observe Fuel Tank Pressure Sensor data display with scan tool. Verify amount of CNG fuel pressure in fuel tank by filling CNG fuel tank at CNG dispensing station. Observe Fuel Tank Pressure Sensor data display after tank is filled. Does FTP sensor indicate fuel pressure near 3600 psi (24,820 kPa) at 70°F (21°C)? If yes, go to next step. If no, go to step 26 .
Start and idle engine. Observe Fuel Tank Pressure Sensor data display with scan tool. Command High Pressure Lock-Off (HPL) solenoid OFF while monitoring Fuel Tank Pressure Sensor data display. Observe Fuel Tank Pressure Sensor data display until engine stalls or switches to gasoline operation. Does Fuel Tank Pressure Sensor data display smoothly indicate fuel pressure decrease and also indicate fuel pressure less than 200 psi (1379 kPa)? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step 26 .
Turn OFF the ignition. Disconnect AF ECM. Turn ON the ignition, with the engine OFF. Measure voltage between Alternative Fuel Level Control circuit and ground with DMM (J 39200). Is voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step 19 .
Connect Alternative Fuel Level Control circuit to ground with a fused jumper. On Bi-fuel (KL6) vehicles press fuel gauge select switch. Observe fuel gauge immediately after jumpering circuit or pressing switch. Does fuel gauge display near empty? If yes, go to step 24 . If no, go to step 27 .
Disconnect cargo/fuel gauge select switch. Probe Fuel Gauge Select Switch Signal circuit with test light connected to battery voltage. Is test light illuminated? If yes, go to step 22 . If no, go to step 29 .
Test Fuel Gauge Select Switch Signal circuit between PCM connector terminal and switch for an open or short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 30 . If no, go to step 29 .
Test Alternative Fuel Level Signal circuit between PCM connector terminal and AF ECM for an open, short to ground or short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 30 . If no, go to step 23 .
Test Fuel Tank Temperature Sensor Signal circuit for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 30 . If no, go to step 25 .
Test Fuel Tank Pressure Sensor Signal circuit for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 30 . If no, go to step 26 .
Repair Fuel Gauge Select Switch Signal circuit for a short to ground condition. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 30 .
Inspect for proper terminal contact at PCM connector. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 30 . If no, go to step 27 .
Inspect for proper terminal contact at AF ECM connector. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 30 . If no, go to step 28 .
Replace Fuel Tank Temperature (FTT) sensor. FTT sensor is not serviceable separately from HPL. After repairs, go to step 30 .
Replace FTP sensor. After repairs, go to step 30 .
Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to step 30 .
Replace AF ECM. After repairs, go to step 30 .
Replace fuel gauge select switch. After repairs, go to step go to next step.
Connect any disconnected components, fuses, etc. With scan tool, clear DTC Information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe MIL and Fuel Indicator Lamp (KL6 only). Observe vehicle performance and driveability. After operating vehicle, inspect AF ECM and PCM for stored DTCs. Does vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

If customers concern is related to fast filling fuel tank refer to the following

Fast-filling CNG fuel tank causes fuel to heat-up and expand.
Fuel temperature may remain hotter than ambient Intake Air Temperature (IAT) for up to 3 hours after filling.
Fuel tank pressure may decrease by up to 800 psi within 3 hours of fast filling. Fuel tank will not completely fill during a fast fill, due to expansion of fuel. Fuel gauge will display full as long as fuel is hot. Fuel gauge display reading will decrease as fuel cools.

FUEL HEATER INOPERATIVE DIAGNOSIS (6.5L)

Note. For component locations, see COMPONENT LOCATIONS .

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor, and a filter. Filter contains coalescer (the device that combines small droplets of water into larger ones) and filter/separator. A fuel lift pump delivers diesel fuel from tank to fuel filter. As fuel enters filter, fuel passes first through fuel heater. Heater contains a thermostatic switch that opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter and water coalescer, where droplets of water-in-fuel combine into larger drops that fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to injection pump, fuel is clean and free of water. Fuel heater is operated by a built-in thermostatic switch. Thermostatic switch completes circuit for fuel heater element when a temperature below 46°F (8°C) is detected.

If water-in-fuel light is operating properly, go to next step. If water-in-fuel light is not operating properly, perform water-in-fuel light diagnosis. See «WATER-IN-FUEL LIGHT ALWAYS ON (6.5L)»(ref-150429-S36671470512002112200000) or «WATER-IN-FUEL LIGHT INOPERATIVE (6.5L)»(ref-150429-S23053818232002111300000) .
Disconnect fuel heater harness connector and remove heater from filter housing. With fuel heater at room temperature, connect ignition voltage circuit of fuel heater to battery voltage and connect ground circuit of fuel heater to ground. Observe heater element. Does heat occur? If yes, go to step 4 . If no, go to next step.
Cool sensor part of fuel heater with ice. With fuel heater below 46°F (8°C), wet heating element with fuel. Connect ignition voltage circuit of fuel heater to battery voltage and connect ground circuit of fuel heater to ground. Observe heating element. Does heat occur? If yes, go to step 5 . If no, go to next step.
Replace fuel heater. After repairs, go to next step.
Operate vehicle under which problem was noted. Does system operate properly? If yes, system is okay. if no, go to step 1 .

FUEL HEATER ALWAYS ON DIAGNOSIS (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor, and a filter. The filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. As fuel enters filter, fuel passes first though fuel heater. Heater contains a thermostatic switch that opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter and water coalescer, where droplets of water-in-fuel combine into larger drops that fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to injection pump, fuel is clean and free of water. Fuel heater is operated by a built-in thermostatic switch. Thermostatic switch completes circuit for fuel heater element when thermostatic switch senses a temperature below 46°F (8°C).

Does water-in-fuel light operate properly? If yes, go to next step. If no, go to «WATER-IN-FUEL LIGHT ALWAYS ON (6.6L)»(ref-150429-S27449140612002112200000) or «WATER-IN-FUEL LIGHT INOPERATIVE (6.6L)»(ref-150429-S20236282362002112200000) .
Disconnect fuel heater connector and remove fuel heater from filter housing. With fuel heater at room temperature, connect Ignition 1 voltage circuit of fuel heater to battery voltage and connect ground circuit of fuel heater to ground. Observe heater element. Does heat occur? If yes, go to step 4 . If no, go to next step.
Cool sensor part of fuel heater with ice. With fuel heater below 46°F (8°C), wet heating element with fuel. Connect Ignition 1 voltage circuit of fuel heater to battery voltage and connect ground circuit of fuel heater to ground. Observe heating element. Does heat occur? If yes, go to step 5 . If no, go to next step.
Replace fuel heater. After repairs, go to next step.
Operate vehicle under which problem was noted. Does system operate properly? If yes, system is okay. If no, go to step 1 .

FUEL HEATER INOPERATIVE DIAGNOSIS (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor, and a filter. Filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. As fuel enters filter, fuel passes through fuel heater. Heater contains a thermostatic switch that opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter and water coalescer, where droplets of water in fuel combine into larger drops that fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to injection pump, fuel is clean and free of water. Fuel heater is operated by a built-in thermostatic switch. Thermostatic switch completes circuit for fuel heater element when thermostatic switch senses a temperature below 46°F (8°C).

Does Water In Fuel light operate properly? If yes, go to next step. If no, go to «WATER-IN-FUEL LIGHT ALWAYS ON (6.6L)»(ref-150429-S27449140612002112200000) or «WATER-IN-FUEL LIGHT INOPERATIVE (6.6L)»(ref-150429-S20236282362002112200000)
Disconnect fuel heater harness connector from top of fuel filter/heater element housing. Turn ON the ignition with the engine OFF. Probe fuel heater Ignition 1 voltage circuit with test light connected to a good ground. See «WIRING DIAGRAMS»(ref-142952) article. Does test light illuminate? If yes, go to next step. If no, go to step 5 .
Probe fuel heater ground circuit at fuel filter/heater element housing with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 10 .
Remove fuel filter from fuel filter/heater element housing. Test Ignition 1 voltage circuit and ground circuit for an open in fuel filter/heater element housing. Did either circuit test open? If yes, go to step 11 . If no, go to step 7 .
Is fuel HT fuse open? If yes, go to next step. If no, go to step 8 .
Disconnect intake air heater harness connector. Probe Ignition 1 voltage circuit with test light connected to battery voltage. Does test light illuminate? If yes, go to step 9 . If no, go to next step.
Remove fuel filter/heater element housing from vehicle. On a bench, cool sensor part of fuel heater with ice. With fuel heater below 46°F (8°C), wet heating element with fuel. Connect Ignition 1 voltage circuit of fuel heater to battery voltage and connect ground circuit of fuel heater to ground on top of housing. Observe heating element. Does heat occur? If yes, go to step 13 . If no, go to step 12 .
Repair open in Ignition 1 voltage circuit between fuel filter/heater element housing and HT fuse. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Repair short to ground on Ignition 1 voltage circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Repair open in ground circuit between fuel filter/heater element housing and chassis ground. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Replace fuel filter/heater element housing. After repairs, go to step 14 .
Replace fuel heater. After repairs, go to step 14 .
Replace intake air heater relay. After repairs, go to step 14 .
Operate vehicle under which problem was noted. Does system operate properly? If yes, system is okay. If no, go to step 1 .

FUEL INJECTION NOZZLE DIAGNOSIS (6.5L)

Note. For component locations, see COMPONENT LOCATIONS .

Injector Balance Test

An injector balance test is performed with scan tool. This test will properly identify a stuck closed or noisy injector nozzle. Typically, a nozzle failure will fall into this criteria.

Install scan tool.
Start and idle engine.
Perform injector balance test on each cylinder. If a suspect nozzle has been located, nozzle can be swapped with adjacent cylinder and balance test can be repeated as a check to positively identify a malfunctioning nozzle.
Locate and replace malfunctioning nozzle and glow plug.

Nozzle Opening Pressure Test

WARNING

DO NOT place your hands or arms near tip of nozzle when testing nozzles. High pressure atomized fuel spray from a nozzle has sufficient penetrating power to puncture flesh and destroy tissue. This may result in blood poisoning. Always enclose nozzle tip in a receptacle, preferably transparent, in order to contain spray.

Note. Nozzle Opening Pressure Test should only be performed on vehicles with high mileage engines that have been overheated or on vehicles that pull heavy loads. False or inaccurate readings can occur if following tests are not performed to this criteria.

Position a nozzle tester on a workbench.
Install one nozzle on tester fitting.
Place a container under nozzle that will deflect nozzle spray and absorb test fluid.
Install 2 clear plastic hoses one inch (25.4 mm) long over leak-off fittings.
Close shut-off valve at pressure gauge.
Operate lever of nozzle tester repeatedly and briskly to fill and flush nozzle with test oil.

Open shut-off valve at pressure gauge 1/4 turn.
Depress tester lever slowly. Record pressure at which needle of pressure gauge stopped. Maximum observed pressure is opening pressure. Some nozzles may pop while other nozzles may drip down (this is not leakage).
Opening pressure for used nozzles should not be less than lower limit of 1500 psi (105 bar) for naturally aspirated engines and 1700 psi (117 bar) for turbo-charged engines.
Replace nozzles which that are less than lower limit.

Nozzle Leak Test

WARNING

Note. Nozzle Leak Test should only be performed on vehicles with high mileage engines that have been overheated or on vehicles that pull heavy loads. False or inaccurate readings can occur if following tests are not performed to this criteria.

Open shut-off valve at pressure gauge one turn.
Blow dry nozzle tip.
Depress lever of manual test stand slowly until gauge reads a pressure of 1400 psi (95 bar). Observe nozzle tip. A drop may form on end of nozzle but should not drop off within a period of 10 seconds.
Replace nozzle assembly if a drop falls during 10 second period.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

Fuel Injector Balance Test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical Diagnostic Trouble Codes (DTCs). During test, Engine Control Module (ECM) turns OFF individual injectors while engine is running and scan tool displays engine RPM. If a fuel injector is turned OFF and there is a different engine speed change observed on scan tool when compared to other cylinders, that cylinder has a fuel injector or engine compression condition. If there is a balance rate of more than 4 mm 3 or less than -4 mm 3 on any cylinder, that cylinder has a fuel injector or engine compression condition. If a fuel injector is turned OFF and engine noise or smoke disappears, that cylinder has a fuel injector or engine compression condition.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138411-S24056483272002041200000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
Are any DTCs set other than P0300, P0301-P0308? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138411-S02438938112002041200000) in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. If no, go to next step.
Start and idle engine. Observe Balancing Rate Cyl. 1-8 parameters with scan tool. Are all Balancing Rate parameters within -4 mm 3 and 4 mm 3 ? If yes, go to step 5 . If no, go to next step.
Graph Fuel Pressure Regulator. See «FUEL PRESSURE REGULATOR GRAPHING»(ref-150429-S17422008132002112500000) under FUEL SYSTEM DIAGNOSIS - HIGH PRESSURE SIDE (6.6L). Is fuel pressure regulator graph normal? If yes, go to step 6 . If no, go to step 8 .
Observe engine speed or other customer concern. Perform Cylinder Power Balance Test in Special Functions. Do any cylinders indicate a different engine speed change than the others, or lessen customer concern? If yes, go to next step. If no, system is okay.
Perform engine compression test. Do any cylinders have low compression? If yes, repair as necessary. See 6.6L V8 DIESEL article in ENGINES. If no, go to next step.
Replace faulty fuel injectors on cylinders that had poor RPM drop, high balance rates, or a noise/smoke change. After repairs, go to step 9 .
Replace fuel pressure regulator. After repairs, go to next step.
Operate vehicle under conditions in which concern occurred. Does system operate normally, with no DTCs or symptoms? If yes, system is okay. If no, go to step 2 .

FUEL RETURN SYSTEM DIAGNOSIS (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

FUEL SYSTEM DIAGNOSIS - CAB & CHASSIS (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

FUEL SYSTEM DIAGNOSIS - PICKUP (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

FUEL SYSTEM DIAGNOSIS - HIGH PRESSURE SIDE (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

Were you directed here from one of the following? Diagnostic Procedure for DTC P1094. SURGES &/OR CHUGGLES symptom under «SYMPTOM DIAGNOSIS»(ref-149956-S01569150402002110400000) under SYMPTOMS (DIESEL) in TROUBLE SHOOTING - NO CODES - TRUCKS article. ROUGH, UNSTABLE, OR INCORRECT IDLE & STALLING under «SYMPTOM DIAGNOSIS»(ref-149956-S01569150402002110400000) under SYMPTOMS (DIESEL) in TROUBLE SHOOTING - NO CODES - TRUCKS article. FUEL INJECTOR BALANCE TEST WITH TECH 2 If yes, go to «FUEL PRESSURE REGULATOR GRAPHING»(ref-150429-S17422008132002112500000) . If no, go to next step.
Remove air duct from air cleaner assembly and turbo inlet.
Remove air intake pipe.
Remove fuel injection pump fuel return rubber hose from junction block. Cap fitting on block with a 3/8" rubber cap to prevent fuel leakage.
Attach a rubber hose with a barbed fitting to fuel injection pump return hose and insert other end into a one gallon clean fuel container.
Remove Ignition 1 relay using Relay Puller Pliers (J 43244).
Remove glow plug controller/relay.
Remove fuel line retainers.
Remove banjo bolt from left rear cylinder head.
Install Black hose of (J 45873) to left rear cylinder head and install other end of hose into one of (J 45873) graduated cylinders.
Remove banjo bolt from leak-off block.
Install other Black hose of (J 45873) to leak-off block and install other end of hose into another (J 45873) graduated cylinders.
Remove banjo bolt from junction block.
Crank engine for 15 seconds while observing fuel pressure relief valve on junction block for fuel leakage. If fuel is leaking from fuel pressure relief valve, replace fuel pressure relief valve. If no fuel is leaking from fuel pressure relief valve, go to next step.
Crank engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into one or both of (J 45873) graduated cylinders.
Elevate hoses to retain fuel in hoses, and empty graduated cylinders into a suitable container.
Install hoses into 2 graduated cylinders.
Crank engine for 15 seconds.
Measure quantity of fuel in each graduated cylinder. If there is more than 12 ml of fuel from either cylinder bank, remove valve cover from that bank. For valve cover removal and installation procedure, see «6.6L V8 DIESEL»(ref-136249) article in ENGINES. Go to next step. If there is less than 12 ml from each cylinder bank, replace fuel injection pump and repeat steps 15 - 19 . If fuel injection pump has already been replaced in this repair and there is less than 12 ml of fuel from each bank, go to step 39 .
Remove return line from injectors.
Install 4 Yellow hoses from (J 45873) to injectors and other end of hoses into each (J 45873) graduated cylinder.
Install 4 injector supply lines. Tighten supply lines to specification. See «REMOVAL, OVERHAUL & INSTALLATION - 6.6L DIESEL»(ref-150848) article.
Connect fuel injection control module wiring harness connectors to enable starter.
Install fuel supply hose. Push hose in until it locks.
Install Black hoses from (J 45873) into same container that fuel injection pump return hose is in. Prime fuel system 30 times to remove air from fuel system. Air will be forced out of system within 2 minutes.
Crank engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into one or more graduated cylinders.
Elevate 4 hoses to retain fuel in hoses, and empty 4 graduated cylinders into a suitable container.
Install hoses in graduated cylinders in numerical order.
Crank engine for 15 seconds.
Measure quantity of fuel in each graduated cylinder. Repeat steps 25 - 30 for all fuel injectors. If there is more than 4 ml of fuel flow from any fuel injector(s), replace high flowing fuel injector(s). After replacement, go to next step. If no fuel injector has a flow of more than 3 ml, install valve cover. After installing valve covers, go to next step.
Were both banks of fuel injectors tested with steps 25 - 30 ? If yes, go to step 40 . If no, go to next step.
Reassemble fuel return line and valve cover.
Ensure hoses are still installed as they were in steps 10) - 13) .
Prime fuel system 30 times to remove air from fuel system. Air will be forced out of system within 2 minutes.
Crank engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into one or both (J 45873) graduated cylinders.
Elevate hoses to retain fuel in hoses, and empty graduated cylinders into a suitable container.
Install hoses into 2 graduated cylinders.
Crank engine for 15 seconds while observing fuel pressure relief valve for fuel leaks. If relief valve leaks, replace relief valve and repeat steps 35 - 38 .
Measure quantity of fuel in each graduated cylinder. If there is more than 12 ml of fuel in either cylinder, perform steps 25 - 30 on bank of fuel injectors with high fuel flow, then go to next step. If both cylinder have less than 12 ml of fuel, go to next step.
Install all disconnected and removed components.
Start and idle engine. You may have to prime fuel system before engine will start.
Connect scan tool to DLC.
Command fuel pressure control to 160 MPa with scan tool. If fuel pressure is more than 145 MPa, system is okay. If fuel pressure is unable to increase to more than 145 MPa, replace fuel injection pump.

This check requires fuel sender and "O" ring to be installed.
Disconnect battery cables.
Drain fuel tank.
Remove fuel tank.
Cap fuel feed tube and fuel return tube on fuel sender.
Connect a piece of hose to filler tube nipple and plug opposite end.
Submerge tank in water or apply a soap solution to outside of tank.
Apply 5 psi (35 kPa) of air pressure to vent hose of fuel tank. A leak will show up as bubbles.

GLOW PLUG SYSTEM DIAGNOSIS (6.5L)

Note. For component locations, see COMPONENT LOCATIONS .

The glow plug system is used to assist in providing heat required to begin combustion during engine starting at cold ambient temperatures. Glow plugs are heated before and during cranking, as well as during engine operation. Powertrain Control Module (PCM) controls glow plug ON times by monitoring coolant temperatures and glow plug voltage. This system check will check glow plugs and glow plug feed circuit coming from relay.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-139779-S23178353562002050900000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.5L CAB & CHASSIS, CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Retrieve DTCs. If DTC P0117, P0118 and/or P0380 is not set, go to next step. If DTC P0117, P0118 and/or P0380 is set, perform appropriate DTC test. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-139779-S39258880492002050900000) in SELF-DIAGNOSTICS - 6.5L CAB & CHASSIS, CHEVY EXPRESS & SAVANA article.
Turn ignition off. Disconnect all glow plug harness connectors. Using a test light connected to battery voltage, probe each glow plug spade terminal at glow plugs. If test light illuminates at each glow plug, go to next step. If test light does not illuminate at each glow plug, go to step 9 .
Ensure all glow plug harness connectors are still disconnected. Turn ignition on with engine off. Using scan tool, command glow plugs on. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at each glow plug harness connector, go to next step. If test light does not illuminate at each glow plug harness connector, go to step 10 .
Using scan tool, command glow plugs off. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at any glow plug harness connector, go to next step. If test light does not illuminate at any glow plug harness connector, go to step 11 .
Remove glow plug relay. Using scan tool, command glow plugs off. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at any glow plug harness connector, go to next step. If test light does not illuminate at any glow plug harness connector, go to step 8 .
Repair short to voltage in Glow Plug Output circuit or Glow Plug Signal circuit. After repairs, go to step 11 .
Replace glow plug relay. After repairs, go to step 11 .
Replace glow plugs that did not illuminate test light. After repairs, go to step 11 .
Repair open in glow plug circuit(s) that did not illuminate test light. After repairs, go to next step.
Operate vehicle under conditions when problem was noted. If system does not operate properly, go to step 1 .

If glow plug relay is stuck in ON position, check for proper operation of glow plugs. When glow plugs are commanded ON by scan tool, an internal PCM timer protects glow plugs from damage by cycling them ON for 3 seconds and then OFF for 12 seconds. Most glow plug system failures are covered by DTC P0380. If no DTCs are stored, vehicle is hard to start, White smoke is present during cranking or after vehicle is started, the most likely cause of failure is glow plugs.

GLOW PLUG SYSTEM DIAGNOSIS (6.6L)

Note. For component locations, see COMPONENT LOCATIONS .

The glow plug system is used to assist in providing heat required to begin combustion during engine starting at cold ambient temperatures. Glow plugs are heated before and during cranking, as well as during engine operation. Engine Control Module (ECM) controls glow plug ON times by monitoring coolant temperatures and glow plug voltage. This system check will check glow plugs and Glow Plug Feed circuit coming from relay/controller.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138411-S24056483272002041200000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
Retrieve DTCs. If DTC P0117, P0118 and/or P0380 is not set, go to next step. If DTC P0117, P0118 and/or P0380 is set, perform appropriate DTC test. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138411-S02438938112002041200000) in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article.
Turn ignition off. Disconnect all glow plug harness connectors. Using a test light connected to battery voltage, probe each glow plug spade terminal at glow plugs. If test light illuminates at each glow plug, go to next step. If test light does not illuminate at each glow plug, go to step 9 .
Ensure all glow plug harness connectors are still disconnected. Turn ignition on with engine off. Using scan tool, command glow plugs on. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at each glow plug harness connector, go to next step. If test light does not illuminate at each glow plug harness connector, go to step 10 .
Using scan tool, command glow plugs off. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at any glow plug harness connector, go to next step. If test light does not illuminate at any glow plug harness connector, go to step 11 .
Remove glow plug relay. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at any glow plug harness connector, go to next step. If test light does not illuminate at any glow plug harness connector, go to step 8 .
Repair short to voltage in Glow Plug Output circuit or Glow Plug Signal circuit. After repairs, go to step 11 .
Replace glow plug relay. After repairs, go to step 11 .
Replace glow plugs that did not illuminate test light. After repairs, go to step 11 .
Repair open in glow plug circuit(s) that did not illuminate test light. After repairs, go to next step.
Operate vehicle under conditions when problem was noted. If system does not operate properly, go to step 1 .

If glow plug relay is stuck in ON position, check for proper operation of glow plugs. When glow plugs are commanded ON by scan tool, an internal ECM timer protects glow plugs from damage by cycling them ON for 3 seconds and then OFF for 12 seconds. Most glow plug system failures are covered by DTC P0380. If no DTCs are stored, vehicle is hard to start, White smoke is present during cranking or after vehicle is started, the most likely cause of failure is glow plugs.

The ignition relay supplies ignition voltage to glow plugs, Fuel Injection Control Module (FICM), Engine Control Module (ECM), fuel rail pressure regulator, Mass Air Flow (MAF) sensor, fuel heater, A/C compressor relay, Daytime Running Lights (DRL) and rear defogger.

If IGN relay fails open

Scan data WILL be available.
Vehicle WILL crank, no-start.
Dash indicator lights WILL illuminate.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138411-S24056483272002041200000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn OFF the ignition. Remove underhood electrical center cover. Remove IGN 1 relay with Relay Puller Pliers (J 43244). Probe IGN 1 relay 12-volt Switch Supply circuit at underhood electrical center terminal with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 8 .
Turn ON the ignition, with the engine OFF. Probe IGN 1 relay 12-volt Coil Supply circuit at underhood electrical center with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 9 .
Probe Ignition 1 Relay Control circuit at underhood electrical center with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 10 .
Turn OFF the ignition. Jumper IGN 1 Relay Switch Supply circuit and IGN 1 Relay Load circuit together using fused jumper wire. Probe ECMRPV and INJR B fuses with test light connected to ground. Does test light illuminate for both fuses? If yes, go to next step. If no, go to step 13 .
Inspect for poor terminal contact at IGN relay underhood electrical center connector. Did you find and correct condition? If yes, go to step 14 . If no, go to next step.
Replace IGN 1 relay. After repairs, go to step 14 .
Repair open or short to ground in 12-volt switch supply to IGN 1 relay. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Repair open or short to ground in 12-volt Coil Supply circuit to IGN 1 relay. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Test IGN 1 Relay Control circuit for an open and repair as necessary. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
Test for poor or intermittent connections at ECM and repair as necessary. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
Replace ECM. Perform ECM relearn procedures. See «PROGRAMMING»(ref-138411-S27281177062002041200000) in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After repairs, go to step 14 .
Replace underhood electrical center. After repairs, go to next step.
Remove all test equipment except scan tool. Reconnect any disconnected components, fuses, etc. Turn ignition OFF for 30 seconds. Start engine and operate vehicle. Observe MIL, vehicle performance and driveability. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138411-S02438938112002041200000) in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article.

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor, and a filter. Filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. A fuel lift pump delivers diesel fuel from tank to fuel filter. As fuel enters filter, fuel passes first through fuel heater. Heater contains a thermostatic switch. Switch opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter. Next, fuel flows through water coalescer. Here droplets of water-in-fuel combine into larger drops and fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to injection pump, fuel is clean and free of water. Solid state water-in-fuel sensor supplies voltage to a probe. When probe touches water, module closes a switch. This completes a circuit to ground to light water-in-fuel light. A time delay circuit in water-in-fuel module grounds lamp briefly to test bulb each time system is turned ON. Fuel heater is operated by a built-in thermostatic switch. When switch is closed, battery voltage is supplied to heater.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-139779-S23178353562002050900000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.5L CAB & CHASSIS, CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn ON the ignition, with the engine OFF. Does water-in-fuel light illuminate briefly, then go out? If yes, go to step 4 . If no, go to next step.
Does water-in-fuel light stay ON? If yes, go to step 5 . If no, go to. «WATER-IN-FUEL LIGHT INOPERATIVE (6.5L)»(ref-150429-S23053818232002111300000)
Operate vehicle under conditions which problem was noted. Does system operate normally? If yes, system is okay. If no, go to step 2 .
Disconnect water-in-fuel sensor harness connector. Turn ON the ignition, with the engine OFF. Probe Water-In-Fuel Indicator Control circuit at harness connector with Test Light (J 34142-B) connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 7 .
Repair short to ground in Water-In-Fuel Indicator Control circuit. After repairs, go to step 8 .
Replace water-in-fuel sensor. After repairs, go to next step.
Start engine. Operate vehicle within conditions under which problem was noted. Does system operate normally? If yes, system is okay. If no, go to step 2 .

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor and a filter. Filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. A fuel lift pump delivers diesel fuel from tank to fuel filter. As fuel enters filter, fuel passes first though fuel heater. Heater contains a thermostatic switch, which opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter and water coalescer, where droplets of water-in-fuel combine into larger drops, that fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to injection pump, fuel is clean and free of water. Solid state water-in-fuel sensor supplies voltage to a probe. When probe touches water, module closes a switch. This completes a circuit to ground and illuminates water-in-fuel light. A circuit in water-in-fuel module grounds light briefly to test bulb each time system is turned ON.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-139779-S23178353562002050900000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.5L CAB & CHASSIS, CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn ON the ignition, with the engine OFF. Does water-in-fuel light come ON briefly? If yes, go to step 6 . If no, go to next step.
Disconnect water-in-fuel sensor. With Test Light (J 34142-B) connected to ground, probe terminal "A" (Pink wire). Verify ignition is ON, with the engine OFF. Does test light illuminate? If yes, go to next step. If no, go to step 7 .
With Test Light (J 34142-B), jumper harness terminals "A" (Pink wire) and "C" (Black wire) with ignition still ON. Does test light illuminate? If yes, go to next step. If no, go to step 9 .
With Test Light (J 34142-B) connected to ground, probe terminal "B" (Yellow/Black wire) of harness connector. Does test light illuminate? If yes, go to step 8 . If no, go to step 10 .
Operate vehicle under which system was noted. Does system operate properly? If yes, system is okay. If no, go to step 2 .
Check Ignition Feed circuit for an open. See «WIRING DIAGRAMS»(ref-142952) article. If a problem is found, repair as necessary. After repairs, go to step 12 .
Check for a poor feed connection at sensor. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step 12 . if no, go to step 11 .
Check Ground circuit for an open. See «WIRING DIAGRAMS»(ref-142952) article. If a problem is found, repair as necessary. After repairs, go to step 12 .
Repair open in Light circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 12 .
Replace water-in-fuel sensor. After repairs, go to step 12 .
Operate vehicle under condition which original problem was noted. Does system operate properly? If yes, system is okay. If no, go to step 2 .

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor and a filter. Filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. As fuel enters filter, fuel passes first through fuel heater. Heater contains a thermostatic switch. Switch opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter. Next, fuel flows through water coalescer. Here droplets of water-in-fuel combine into larger drops and fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to fuel injection pump, fuel is clean and free of water. When there is water-in-fuel filter, water-in-fuel sensor closes a switch. This completes a circuit to ground for Engine Control Module (ECM). Message center in Instrument Panel Cluster (IPC) indicates water-in-fuel when ECM commands IPC to indicate condition. This is done through data link communications, and command is available on scan tool.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138411-S24056483272002041200000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
Start and idle engine. Observe message center in instrument cluster. Does message center indicate water-in-fuel? If yes, go to next step. If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Perform Water-In-Fuel Draining Procedure. See «WATER-IN-FUEL DRAINING PROCEDURE (6.6L)»(ref-150429-S36730531432002112200000) . After performing procedure, go to next step.
Start and idle engine. Observe message center in instrument cluster. Does message center indicate water-in-fuel? If yes, go to next step. If no, go to step 10 .
Disconnect water-in-fuel sensor. Does scan tool display Water-In-Fuel parameter is OFF? If yes, go to step 8 . If no, go to next step.
Turn OFF the ignition. Disconnect ECM. Probe Water-In-Fuel Indicator Control circuit with a test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 9 .
Repair short to ground in Water-In-Fuel Indicator Control circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 10 .
Replace water-in-fuel sensor. After repairs, go to step 10 .
Replace ECM. Perform ECM relearn procedures. See «PROGRAMMING»(ref-138411-S27281177062002041200000) in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 3 .

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor and a filter. Filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. As fuel enters filter, fuel passes first through fuel heater. Heater contains a thermostatic switch. Switch opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter. Next, fuel flows through water coalescer. Here droplets of water-in-fuel combine into larger drops and fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to fuel injection pump, fuel is clean and free of water. When there is water-in-fuel filter, water-in-fuel sensor closes a switch. This completes a circuit to ground for Engine Control Module (ECM). Message center in Instrument Panel Cluster (IPC) indicates water-in-fuel when ECM commands IPC to indicate condition. This is done through data link communications, and command is available on scan tool.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138411-S24056483272002041200000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn ON the ignition, with the engine OFF. Does battery indicator illuminate in message center in Instrument Panel Cluster? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - INSTRUMENT CLUSTER under SELF-DIAGNOSTIC SYSTEM in appropriate ANALOG INSTRUMENT PANEL article.
Start and run engine. Does message center in IPC indicate water-in-fuel? If yes, go to «WATER-IN-FUEL DRAINING PROCEDURE (6.6L)»(ref-150429-S36730531432002112200000) . If no, go to next step.
Observe Water-In-Fuel parameter of scan tool. Does scan tool indicate light is being commanded ON? If yes, go to step 13 . If no, go to next step.
Disconnect water-in-fuel sensor. Connect a 3-amp fused jumper wire between Control circuit and Ground circuit of water-in-fuel sensor. See «WIRING DIAGRAMS»(ref-142952) article. Does scan tool indicate light is being commanded ON? If yes, go to step 10 . If no, go to next step.
Connect a 3-amp fused jumper wire between Control circuit of water-in-fuel sensor and a good ground. Does scan tool indicate light is being commanded ON? If yes, go to step 9 . If no, go to next step.
Test Control circuit of water-in-fuel sensor for an open. See «WIRING DIAGRAMS»(ref-142952) article. Did you find a problem? If yes, go to next step. If no, go to step 11 .
Repair open in Water-In-Fuel Sensor Control circuit. After repairs, go to step 14 .
Repair open condition in Water-In-Fuel Sensor Ground circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Inspect the connections at the water-in-fuel sensor. See «WIRING DIAGRAMS»(ref-142952) article. Repair as necessary. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
Inspect connections at ECM. See «WIRING DIAGRAMS»(ref-142952) article. Repair as necessary. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
Replace water-in-fuel sensor. After repairs, go to step 14 .
Replace ECM. Perform ECM relearn procedures. See «PROGRAMMING»(ref-138411-S27281177062002041200000) in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 1 .

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (2.2L SONOMA & S10 PICKUP)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138342-S08198199552002040800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (2.2L SONOMA & S10 PICKUP)»(ref-150429-S16079234992002111300000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 56-62 psi (384-425 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (2.2L SONOMA & S10 PICKUP)»(ref-149936-S35718292332002110100000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (2.2L SONOMA & S10 PICKUP)»(ref-149936-S35718292332002110100000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Connect Fuel Injector Tester (J 39021) to fuel injector. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 4 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (3.4L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (3.4L)»(ref-150429-S18838943552002111300000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 52-59 psi (358-405 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (3.4L)»(ref-149936-S29348623012002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (3.4L)»(ref-149936-S29348623012002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Connect Fuel Injector Coil/Balance Tester (J 39021), Injector Test Adapter Box (J 39021-210), and Fuel Injector Test Harness (J 39021-410) to fuel injector multi-way connector. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 5 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-132531-S16910731432002012100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (4.2L)»(ref-150429-S28916088292002112600000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 48-54 psi (334-375 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.2L)»(ref-149936-S28337785802002112600000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.2L)»(ref-149936-S28337785802002112600000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Disconnect multi-way harness connector of fuel injectors. Connect Fuel Injector Tester (J 39021) to Ignition 1 Voltage circuit terminal and appropriate Fuel Injector Control circuit terminal using Connector Test Adapter Kit (J 35616-A). Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 6 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.3L VIN W & X)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937), «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (4.3L VIN W & X)»(ref-150429-S40847313502002112700000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. On VIN W engines, fuel pressure should be 60-66 psi (414-455 kPa). On VIN X engines, fuel pressure should be 55-62 psi (379-427 kPa). Is fuel pressure as specified? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.3L)»(ref-149936-S33836779402002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.3L)»(ref-149936-S33836779402002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Disconnect multi-way harness connector of fuel injectors. Connect Fuel Injector Tester (J 39021), Injector Selector Switch Box (J 39021-210), and Injector Test Adapter (J 39021-301) to fuel meter body. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 7 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.8L, 5.3L & 6.0L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138163-S11395166402002032500000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (4.8L, 5.3L & 6.0L)»(ref-150429-S04952862872002112700000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. On VIN T, U and V (gasoline) engines, fuel pressure should be 55-62 psi (379-427 kPa). On VIN Z (flex-fuel) engines, fuel pressure should be 48-54 psi (335-375 kPa). Is fuel pressure as specified? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Disconnect multi-way harness connector of fuel injectors. Connect Fuel Injector Tester (J 39021) to a fuel injector. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 8 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (5.0L & 5.7L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138116-S40610776842002032000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (5.0L & 5.7L)»(ref-150429-S42558538042002112700000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure 60-66 psi (414-455 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (5.0L & 5.7L)»(ref-149936-S20567619602002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (5.0L & 5.7L)»(ref-149936-S20567619602002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Connect Fuel Injector Tester (J 39021) and Injector Tester Adapter (J 39021-380) to a fuel injector. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 9 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (8.1L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138305-S37770098362002040400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (8.1L)»(ref-150429-S00344373762002112700000). After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure 55-62 psi (379-427 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
Connect Fuel Injector Tester (J 39021) and Injector Tester Adapter (J 39021-380) to a fuel injector. Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 10 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (2.2L SONOMA & S10 PICKUP)

Note. For component locations, see COMPONENT LOCATIONS .

Scan tool first energizes fuel pump and then injectors for a precise amount of time allowing a measured amount of fuel into manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138342-S08198199552002040800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (2.2L SONOMA & S10 PICKUP)»(ref-150429-S16079234992002111300000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 56-62 psi (384-425 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (2.2L SONOMA & S10 PICKUP)»(ref-149936-S35718292332002110100000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (2.2L SONOMA & S10 PICKUP)»(ref-149936-S35718292332002110100000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (3.4L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (3.4L)»(ref-150429-S18838943552002111300000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 52-59 psi (358-405 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (3.4L)»(ref-149936-S29348623012002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (3.4L)»(ref-149936-S29348623012002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-132531-S16910731432002012100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (4.2L)»(ref-150429-S28916088292002112600000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 48-54 psi (334-375 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.2L)»(ref-149936-S28337785802002112600000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.2L)»(ref-149936-S28337785802002112600000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.3L VIN W & X)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (4.3L VIN W & X)»(ref-150429-S40847313502002112700000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. On VIN W engines, fuel pressure should be 60-66 psi (414-455 kPa). On VIN X engines, fuel pressure should be 55-62 psi (379-427 kPa). Is fuel pressure as specified? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.3L)»(ref-149936-S33836779402002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.3L)»(ref-149936-S33836779402002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.8L, 5.3L & 6.0L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138163-S11395166402002032500000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (4.8L, 5.3L & 6.0L)»(ref-150429-S04952862872002112700000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. On VIN T, U and V (gasoline) engines, fuel pressure should be 55-62 psi (379-427 kPa). On VIN Z (flex-fuel) engines, fuel pressure should be 48-54 psi (335-375 kPa). Is fuel pressure as specified? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138116-S40610776842002032000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (5.0L & 5.7L)»(ref-150429-S42558538042002112700000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure 60-66 psi (414-455 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (5.0L & 5.7L)»(ref-149936-S20567619602002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (5.0L & 5.7L)»(ref-149936-S20567619602002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR BALANCE TEST WITH TECH 2 (8.1L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138305-S37770098362002040400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Perform «FUEL INJECTOR COIL TEST (8.1L)»(ref-150429-S00344373762002112700000) . After performing Fuel Injector Coil Test, go to next step.
Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure 55-62 psi (379-427 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM PRESSURE TEST (4.8L, 5.3L, 6.0L & 8.1L)»(ref-149936-S38768567762002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. If no, go to next step.
With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press Enter. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing Pulse Injector button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press Enter again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Replace affected fuel injectors. After repairs, go to next step.
Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, system is okay.

FUEL INJECTOR CIRCUIT DIAGNOSIS (2.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138342-S08198199552002040800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After performing Diagnostic System Check - Engine Controls, go to next step.
Are any fuel injector DTCs set? If yes, go to «DTC P0201-P0204: INJECTOR CONTROL CIRCUIT»(ref-138342-S23089834932002040800000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. If no, go to next step.
Inspect ECM 1 fuse. Is ECM 1 fuse open? If yes, go to next step. If no, go to step 6 .
Turn OFF the ignition. Disconnect multi-way harness connector of fuel injectors. Probe Ignition 1 Voltage Supply circuit of fuel injector, fuse side, with test light connected to battery voltage. Does test light illuminate? If yes, go to step 9 . If no, go to next step.
Turn ON the ignition, with the engine OFF. Does test light illuminate? If yes, go to step 13 . If no, go to step 8 .
Turn OFF the ignition. Disconnect multi-way harness connector of fuel injectors. Probe Ignition 1 Voltage Supply circuit of fuel injector, fuse side, with test light connected to a good ground. Crank engine. Does test light illuminate while cranking engine? If yes, go to next step. If no, go to step 10 .
Test for continuity between Ignition 1 voltage supply terminal and a fuel injector terminal, at multi-way harness connector, fuel injector side. Does DMM display OL? If yes, go to step 11 . If no, go to step 12 .
Test Ignition 1 Voltage Supply circuit of fuel injector, between multi-way harness connector and fuel injectors for a short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Repair short to ground in Ignition 1 Voltage Supply circuit of fuel injector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Repair open in Ignition 1 Voltage Supply circuit of fuel injector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Repair Ignition 1 Voltage Supply circuit of fuel injectors for an open or high resistance, between multi-way connector and splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 14 .
Repair poor connection at multi-way harness connector. After repairs, go to step 14 .
Repair short to a PCM ground in Ignition 1 Voltage Supply circuit of fuel injector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 3 .

Monitoring Fuel Injector circuit status with scan tool, while moving fuel injector harness, may help isolate an intermittent condition.
Performing Fuel Injector Coil test may help isolate an intermittent condition. See «FUEL INJECTOR COIL TEST (2.2L SONOMA & S10 PICKUP)»(ref-150429-S16079234992002111300000) .
For an intermittent condition, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR CIRCUIT DIAGNOSIS (4.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-132531-S16910731432002012100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
Are any fuel injector DTCs set? If yes, go to «DTC P0201-P0206: FUEL INJECTOR CONTROL CIRCUIT»(ref-132531-S20400196782002012100000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. If no, go to next step.
Turn OFF the ignition. Disconnect multi-way harness connector of fuel injectors. Turn ON the ignition, with the engine OFF. Probe Ignition 1 Voltage Supply circuit of fuel injector, fuse side, with test light connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step 5 .
Test for continuity between Ignition 1 voltage supply terminal and a fuel injector terminal, at multi-way harness connector, fuel injector side. Does DMM display OL? If yes, go to step 6 . If no, go to step 7 .
Repair open in Ignition 1 Voltage Supply circuit between PCM 1 fuse and multi-way connector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 8 .
Repair Ignition 1 Voltage Supply circuit of fuel injectors for an open or high resistance, between multi-way connector and splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 8 .
Repair poor connection at multi-way harness connector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 3 .

Monitoring Fuel Injector circuit status with scan tool, while moving fuel injector harness, may help isolate an intermittent condition.
Performing Fuel Injector Coil test may help isolate an intermittent condition. See «FUEL INJECTOR COIL TEST (4.2L)»(ref-150429-S28916088292002112600000) .
For an intermittent condition, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR CIRCUIT DIAGNOSIS (4.3L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Is DTC P0200 set? If yes, go to DTC P0200: FUEL INJECTOR CONTROL CIRCUIT under DIAGNOSTIC TESTS in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. If no, go to next step.
Inspect ECM 1 fuse. Is ECM 1 fuse open? If yes, go to next step. If no, go to step 6 .
Turn OFF the ignition. Remove engine cover. Disconnect harness connector of fuel injectors. Probe Ignition 1 Voltage Supply circuit of a fuel injector, fuse side, with test light connected to battery voltage. Does test light illuminate? If yes, go to step 8 . If no, go to next step.
Turn ON the ignition, with the engine OFF. Does test light illuminate? If yes, go to step 11 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S33028778722002120300000) .
Turn OFF the ignition. Remove engine cover. Disconnect harness connector of fuel injectors. Turn ON the ignition, with the engine OFF. Probe Ignition 1 Voltage Supply circuit of fuel injector, fuse side, with test light connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step 9 .
Test for continuity between ECM 1 fuse and Ignition 1 voltage supply terminal of a fuel injector. Does DMM display a resistance more than 5 ohms? If yes, go to step 10 . If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Test Ignition 1 Voltage Supply circuit of fuel injectors for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 12 .
Repair open in Ignition 1 Voltage Supply circuit of fuel injectors. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 12 .
Repair high resistance in Ignition 1 Voltage Supply circuit of fuel injectors. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 12 .
Repair short to a PCM ground in Ignition 1 Voltage Supply circuit of fuel injectors. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 3 .

Monitoring Fuel Injector circuit status with scan tool, while moving fuel injector harness, may help isolate an intermittent condition.
Performing Fuel Injector Coil test may help isolate an intermittent condition. See «FUEL INJECTOR COIL TEST (4.3L VIN W & X)»(ref-150429-S40847313502002112700000) .
For an intermittent condition, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL INJECTOR COIL TEST (2.2L SONOMA & S10 PICKUP)

Note. For component locations, see COMPONENT LOCATIONS .

Powertrain Control Module (PCM) enables appropriate fuel injector on intake stroke for each cylinder. A voltage is supplied directly to fuel injectors. PCM controls each fuel injector by grounding Control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high, or too low, will affect engine driveability. A Fuel Injector Control circuit Diagnostic Trouble Code (DTC) may not set, but a misfire may be apparent. Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138342-S08198199552002040800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. See «WIRING DIAGRAMS»(ref-142952) article. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S26558357422002112700000) .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 3 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S26558357422002112700000) . If no, go to next step.
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help to isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (2.2L SONOMA & S10 PICKUP)»(ref-150429-S06491784702002111300000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (2.2L SONOMA & S10 PICKUP)»(ref-150429-S32024841752002112600000) .

FUEL INJECTOR COIL TEST (3.4L)

Note. For component locations, see COMPONENT LOCATIONS .

Powertrain Control Module (PCM) enables appropriate fuel injector on intake stroke for each cylinder. A voltage is supplied directly to fuel injectors. PCM controls each fuel injector by grounding Control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low, will affect engine driveability. A Fuel Injector Control circuit Diagnostic Trouble Code (DTC) may not set, but a misfire may be apparent. Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. See «WIRING DIAGRAMS»(ref-142952) article. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S10965374952002112700000) .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 3 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S10965374952002112700000) . If no, go to next step.
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (3.4L)»(ref-150429-S02807344132002112600000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (3.4L)»(ref-150429-S04410177162002112600000) .

FUEL INJECTOR COIL TEST (4.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Control module enables appropriate fuel injector on intake stroke for each cylinder. A voltage is supplied directly to fuel injectors. Control module controls each fuel injector by grounding Control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low, will affect engine driveability. A Fuel Injector Control circuit Diagnostic Trouble Code (DTC) may not set, but a misfire may be apparent. Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-132531-S16910731432002012100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. See «WIRING DIAGRAMS»(ref-142952) article. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S02351030692002112700000) .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 3 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S02351030692002112700000) . If no, go to next step.
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.2L)»(ref-150429-S12395922072002112600000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.2L)»(ref-150429-S27545051882002112600000) .

FUEL INJECTOR COIL TEST (4.3L VIN W & X)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. See «WIRING DIAGRAMS»(ref-142952) article. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S36976566222002112700000) .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 3 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S36976566222002112700000) . If no, go to next step.
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.3L VIN W & X)»(ref-150429-S37135728862002112600000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.3L VIN W & X)»(ref-150429-S10296400262002112600000) .

FUEL INJECTOR COIL TEST (4.8L, 5.3L & 6.0L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. See «WIRING DIAGRAMS»(ref-142952) article. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S10337400712002112700000) .
Disconnect fuel injector multi-way harness connector. With DMM, measure resistance of each fuel injector between Ignition Feed circuit and Fuel Injector Control circuit, at multi-way connector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 3 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S10337400712002112700000) . If no, go to next step.
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.8L, 5.3L & 6.0L)»(ref-150429-S32879109402002112700000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.8L, 5.3L & 6.0L)»(ref-150429-S21218923612002112700000) .

FUEL INJECTOR COIL TEST (5.0L & 5.7L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138116-S40610776842002032000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Remove engine cover. Measure resistance of each fuel injector with DMM. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S34759515562002112700000) .
Measure and record resistance of each fuel injector with DMM. Subtract lowest resistance value from highest resistance value. Is difference more than 3 ohms? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(ref-150429-S34759515562002112700000) .
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest individual fuel injector resistance value from average resistance value. Subtract highest individual fuel injector resistance value from average resistance value. Replace fuel injector(s) that displays greatest resistance difference from average. After repairs, go to step 7 .
Replace fuel injector(s) that are out of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (5.0L & 5.7L)»(ref-150429-S18352766332002112700000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (5.0L & 5.7L)»(ref-150429-S05727213892002112700000) .

FUEL INJECTOR COIL TEST (8.1L)

Note. For component locations, see COMPONENT LOCATIONS .

Powertrain Control Module (PCM) enables appropriate fuel injector on intake stroke for each cylinder. A voltage is supplied directly to fuel injectors. PCM controls each fuel injector by grounding Control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low, will affect engine driveability. A Fuel Injector Control circuit Diagnostic Trouble Code (DTC) may not set, but a misfire may be apparent. Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138305-S37770098362002040400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
Measure resistance of each fuel injector with DMM. Do any fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, go to «DIAGNOSTIC AIDS»(ref-150429-S18031581952002112700000) .
Measure resistance of each fuel injector with DMM. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is difference equal to, or less than 3 ohms? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S18031581952002112700000) . If no, go to next step.
Add all fuel injector resistance values, to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Monitoring misfire current counters or misfire graph, may help isolate fuel injector that is causing condition.
Operating vehicle over a wide temperature range may help isolate fuel injector that is causing condition.
Perform fuel injector coil test within conditions of customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
If fuel injector coil test does not isolate condition, perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (8.1L)»(ref-150429-S35898155752002112700000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2 (8.1L)»(ref-150429-S21926041702002112700000) .

When ignition is on, control module enables fuel pump relay, which powers fuel pump on. Fuel pump remains on as long as engine is cranking or running and control module receives ignition reference pulses. If there are no ignition reference pulses, control module commands fuel pump off within 2 seconds after ignition was switched to ON position or if engine stops.

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn ON the ignition, with the engine OFF. Command fuel pump relay ON and OFF with a scan tool. Does fuel pump turn ON and OFF? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to next step.
Command fuel pump relay ON and OFF with scan tool. Do you hear a click when you command fuel pump relay ON and OFF? If yes, go to step 9 . If no, go to next step.
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Probe Control circuit of fuel pump relay with a test light that is connected to a good ground. Command fuel pump relay ON and OFF with scan tool. Does test light turn ON and OFF? If yes, go to next step. If no, go to step 6 .
Connect a test light between Control circuit of fuel pump relay and ground circuit of fuel pump relay. Command fuel pump relay ON and OFF with scan tool. Does test light turn ON and OFF? If yes, go to step 19 . If no, go to step 22 .
Does test light remain illuminated with each command? If yes, go to next step. If no, go to step 8 .
Test Control circuit of fuel pump relay for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct condition? If yes, go to step 27 . If no, go to step 26 .
Test Control circuit of fuel pump relay for a short to ground or an open. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 20 .
Turn ON the ignition, with the engine OFF. Does fuel pump operate continuously? If yes, go to next step. If no, go to step 11 .
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Does fuel pump operate continuously? If yes, go to step 21 . If no, go to step 25 .
Is fuel pump fuse open? If yes, go to next step. If no, go to step 14 .
Test supply voltage circuit of fuel pump for a grounded circuit between fuel pump fuse and fuel pump. See «WIRING DIAGRAMS»(ref-142952) article. Replace fuel pump fuse if necessary. Did you find and correct the condition? If yes, go to step 27 . If no, go to next step.
Install all disconnected electrical components. Install a new fuel pump fuse. With scan tool, turn ON fuel pump. Is fuel pump fuse open? If yes, go to step 24 . If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Probe battery voltage circuit of fuel pump relay switch with a test light that is connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step 23 .
Connect a 20-amp fused jumper wire between battery voltage circuit of fuel pump relay switch and supply voltage circuit of fuel pump. Does fuel pump operate? If yes, go to step 19 . If no, go to next step.
Test supply voltage circuit of fuel pump for an open or high resistance between fuel pump relay and fuel pump. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 27 . If no, go to next step.
Test ground circuit of fuel pump for an open or high resistance. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 27 . If no, go to next step.
Inspect for poor connections at fuel pump. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 24 .
Inspect for poor connections at fuel pump relay. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 25 .
Inspect for poor connections at harness connector of PCM. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 26 .
Repair supply voltage circuit of fuel pump for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 27 .
Repair open in ground circuit of fuel pump relay. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 27 .
Repair open in battery voltage circuit of fuel pump relay switch. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 27 .
Replace fuel pump. Replace fuel pump fuse if necessary. After repairs, go to step 27 .
Replace fuel pump relay. After repairs, go to step 27 .
Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to step 27 .
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

When you turn ON the ignition switch, the control module enables fuel pump relay which powers fuel pump on. Fuel pump remains on as long as engine is cranking or running and control module receives ignition reference pulses. If there are no ignition reference pulses, control module shuts fuel pump off within 2 seconds after ignition was switched to ON position or if engine stops.

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Install scan tool. Turn ON the ignition, with the engine OFF. With scan tool, command fuel pump relay ON and OFF. Does fuel pump turn ON and OFF? If yes, go to «DIAGNOSTIC AIDS»(ref-150429-S29057811182002112000000) . If no, go to next step.
With scan tool, command fuel pump relay ON and OFF. Do you hear a click when you command fuel pump relay ON and OFF? If yes, go to step 9 . If no, go to next step.
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Probe Control circuit of fuel pump relay with a test light that is connected to a good ground. With scan tool, command fuel pump ON and OFF. Does test light turn ON and OFF? If yes, go to next step. If no, go to step 6 .
Connect test light between Control circuit of fuel pump relay and ground circuit of fuel pump relay. With scan tool, command fuel pump ON and OFF. Does test light turn ON and OFF? If yes, go to step 21 . If no, go to step 24 .
Does test light remain illuminated with each command? If yes, go to next step. If no, go to step 8 .
Test Control circuit of fuel pump relay for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 29 . If no, go to step 28 .
Test Control circuit of fuel pump relay for a short to ground or an open. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 29 . If no, go to step 22 .
Turn ON the ignition, with the engine OFF. Does fuel pump operate continuously? If yes, go to next step. If no, go to step 11 .
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Does fuel pump operate continuously? If yes, go to step 23 . If no, go to step 27 .
Is fuel pump fuse open? If yes, go to next step. If no, go to step 14 .
Disconnect fuel pump harness in-line connector located near fuel tank. Test fuel pump supply voltage circuit for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. Replace fuel pump fuse if necessary. Did you find and correct the condition? If yes, go to step 29 . If no, go to next step.
Lower fuel tank if necessary. Test or inspect fuel tank electrical harness for damage to harness or a grounded circuit. Replace fuel pump fuse if necessary. Did you find and correct the condition? If yes, go to step 29 . If no, go to step 20 .
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Probe battery positive voltage circuit of fuel pump relay with a test light connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step 25 .
Connect a 10-amp fused jumper wire between battery positive voltage circuit and fuel pump supply voltage circuit in fuel pump cavity. Does fuel pump operate? If yes, go to step 21 . If no, go to next step.
Disconnect fuel pump harness in-line connector located near fuel tank. Test fuel pump supply voltage circuit for an open or high resistance between fuel pump relay and in-line connector. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 29 . If no, go to next step.
Test ground circuit of fuel pump for an open or high resistance between body pass through connector and ground. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 29 . If no, go to next step.
Inspect for poor connections at fuel pump in-line connector to body pass through connector. Did you find and correct the condition? If yes, go to step 29 . If no, go to next step.
Lower fuel tank. Test or inspect fuel tank electrical harness for damage to harness or an open circuit. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 29 . If no, go to step 26 .
Connect all disconnected components. Install a NEW fuel pump fuse. With scan tool, command fuel pump ON. Is fuel pump fuse open? If yes, go to step 26 . If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Inspect for poor connections at fuel pump relay. Did you find and correct the condition? If yes, go to step 29 . If no, go to step 27 .
Inspect for poor connections at harness of PCM. Did you find and correct the condition? If yes, go to step 29 . If no, go to step 28 .
Repair fuel pump supply voltage circuit for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 29
Repair fuel pump relay ground circuit for an open ground. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 29
Repair battery positive voltage circuit of fuel pump relay for an open. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 29
Replace fuel pump. Replace fuel pump fuse, if necessary. After repairs, go to step 29 .
Replace fuel pump relay. After repairs, go to step 29
Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After repairs, go to step 29
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Listen for an audible hiss from fuel pump when fuel pump relay is commanded ON. A vibration in fuel feed line when fuel pump relay is commanded ON indicates fuel pump is operating. If condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.

When you turn ON the ignition switch, control module enables fuel pump relay, which powers fuel pump on. Fuel pump remains on as long as engine is cranking or running and control module receives ignition reference pulses. If there are no ignition reference pulses, control module shuts fuel pump off within 2 seconds after ignition was switched to ON position or if engine stops.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138116-S40610776842002032000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn ON the ignition, with the engine OFF. Command fuel pump relay ON and OFF with scan tool. Does fuel pump relay click when commanded with scan tool? If yes, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to next step.
Command fuel pump relay ON and OFF with scan tool. Do you hear a click when you command fuel pump relay ON and OFF? If yes, go to step 9 . If no, go to next step.
Turn OFF the ignition. Disconnect fuel pump relay. Turn ON the ignition, with the engine OFF. Probe Control circuit of fuel pump relay with test light that is connected to a good ground. Command fuel pump relay ON and OFF with scan tool. Does test light turn ON and OFF when commanded with scan tool? If yes, go to next step. If no, go to step 6 .
Connect test light between Control circuit of fuel pump relay and ground circuit of fuel pump relay. Command fuel pump relay ON and OFF with scan tool. Does test light turn ON and OFF when commanded with scan tool? If yes, go to step 19 . If no, go to step 21 .
Does test light remain illuminated? If yes, go to next step. If no, go to step 8 .
Test Control circuit of fuel pump relay for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
Test Control circuit of fuel pump relay for a short to ground or an open. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 20 .
Turn ON the ignition, with the engine OFF. Does fuel pump operate continuously? If yes, go to next step. If no, go to step 11 .
Test supply voltage circuit of fuel pump for a short to voltage. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 23
Inspect fuel pump fuse. Is fuel pump fuse open? If yes, go to next step. If no, go to step 14 .
Test supply voltage circuit of fuel pump between fuel pump fuse and fuel pump for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. Replace fuel pump fuse. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
Install all disconnected electrical components. Install a new fuel pump fuse, if necessary. Turn ON fuel pump with scan tool. Inspect fuel pump fuse. Is fuel pump fuse open? If yes, go to step 22 . If no, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
Test battery voltage circuit of fuel pump relay switch for an open. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
Connect a 20-amp fused jumper wire between battery voltage circuit of pump relay switch and supply voltage circuit of fuel pump. Does fuel pump operate? If yes, go to step 19 . If no, go to next step.
Test supply voltage between fuel pump relay and fuel pump for an open or high resistance. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
Test ground circuit of fuel pump for an open or high resistance. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
Inspect for poor connections at fuel pump. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 22 .
Inspect for poor connections at fuel pump relay. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 23 .
Inspect for poor connections at harness connector of PCM. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
Repair open fuel pump relay ground circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 25 .
Replace fuel pump. Replace fuel pump fuse if necessary. After repairs, go to step 25 .
Replace fuel pump relay. After repairs, go to step 25 .
Replace PCM. Perform PCM relearn procedures. See «PROGRAMMING»(ref-138116-S27502480672002032000000) in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA article. After repairs, go to next step.
Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

FUEL SYSTEM PRESSURE TEST

Note. For fuel system pressure testing, see appropriate FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.

IDLE AIR CONTROL SYSTEM DIAGNOSIS

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Set parking brake and block drive wheels. Install scan tool. Start engine. Turn all accessories off. Using scan tool RPM control function, slowly increment engine speed to 1700 RPM, then to 600 RPM. Then to 1700 RPM. Exit RPM control function. Did the engine speed stabilize within specifications during the above test? See «RPM VARIATION LIMITS»(ref-150429-S03048895272002112700000) table. If yes, see «DIAGNOSTIC AIDS»(ref-150429-S05935398192002112700000) . If no, go to next step.
Turn ignition off. Disconnect IAC valve harness connector. See WIRING DIAGRAMS article. Connect IAC System Motor Analyzer (J 37027-A) to IAC valve. Start engine. Using IAC system motor analyzer, command IAC valve in until about 600 RPM is reached and then command IAC valve out until about 1700 RPM is reached. Return engine RPM to desired idle as indicated on scan tool data list. Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the IAC valve was commanded in and out? If yes, go to step 5 . If no, go to next step.
Did you observe an excessively high idle condition that could not be controlled with the IAC motor driver during the last test? If yes, go to step 11 . If no, go to step 12 .
Using a test light connected to ground, probe one IAC valve circuit at IAC valve harness connector. See WIRING DIAGRAMS article. Start engine. Using IAC system motor analyzer, command low RPM while observing scan tool until IAC counts start to increment, then command high RPM until IAC counts start to increment. Observe test light while incrementing IAC counts. Return engine to idle as indicated on scan tool data list. Repeat procedure for other three IAC valve circuits. Did the test light remain ON, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the above test? If yes, go to step 10 . If no, go to next step.
Did the test light remain OFF, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the above test? If yes, go to step 9 . If no, go to next step.
Using Connector Test Adapter Kit (J 35616-A) connect a test light between IAC coil "A" low circuit and IAC coil "A" high circuit at IAC valve harness connector. Using IAC system motor driver, command low RPM while observing scan tool until IAC counts start to increment, then command high RPM until IAC counts start to increment. Observe test light while incrementing IAC counts. Return engine speed to desired idle as indicated on scan tool data list. Repeat procedure on IAC coil "B" low circuit and IAC coil "B" high circuit. Did the test light stay illuminated, never flashing, while the IAC counts where incrementing during the above test? If yes, go to next step. If no, go to step 17 .
Check for poor connection at IAC valve harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
Turn ignition off. Disconnect PCM harness connectors. With a DMM, test the circuit where the test light remained off for the following: An open circuit. A short to ground. A short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
Turn ignition on. With a DMM, test the circuit where the test light remained illuminated for the following: A short to voltage. A short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
Visually and physically inspect for the following: Throttle body damage and tampering. Skewed TP sensor signal. Throttle lever screw tampering (if equipped). Vacuum leaks. Faulty, incorrectly installed PCV valve and hose (if equipped). Throttle shaft binding. Throttle linkage or cruise control linkage binding (if equipped). Remove IAC valve. Inspect for the following: Clogged IAC passage. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Excessive deposits on IAC valve pintle. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
Visually and physically inspect for the following: Throttle body damage and tampering. Throttle lever screw tampering (if equipped). Restricted air intake system. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Remove IAC valve and inspect for excessive deposits on IAC valve pintle and in IAC valve passage. Repair as necessary. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
Check for poor PCM harness connections. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
Disconnect the PCM harness connectors. With a DMM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
Check for poor IAC valve harness connection. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
Replace IAC valve. After repairs, go to step 18 .
Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
Reconnect any disconnected components. Use the scan tool to clear any DTCs that may have set. Turn OFF the ignition for 30 seconds. Operate the vehicle within conditions to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step 2 .
With a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, system is okay.

Inspect for the following conditions

A skewed high Throttle Position (TP) sensor.
Restricted air intake system.
Objects blocking the IAC passage or throttle bore.
The correct Positive Crankcase Ventilation (PCV) valve.
A properly installed PCV valve.
Proper operation of the PCV valve.
Proper operation and installation of all air intake components.
Proper installation and operation of the Mass Air Flow (MAF) sensor, if equipped.
Evidence of damage or tampering of the following components: The throttle stop screw. The throttle plate. The throttle shaft. The throttle linkage. The cruise control linkage, if equipped.
Excess deposits in the IAC passage or on the IAC pintle.
Excess deposits in the throttle bore or on the throttle plate Vacuum leaks.
Excess load on engine, such as energy-draining conditions of the transmission, power steering, or alternator.
A high or unstable idle condition. This condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. See TROUBLE SHOOTING - NO CODES - TRUCKS article.
A low or unstable idle condition. This condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. See TROUBLE SHOOTING - NO CODES - TRUCKS article.
An intermittent condition.

Engine	Maximum RPM Less Than Commanded RPM	Maximum RPM More Than Commanded RPM
2.2L (A/T)	60	60
2.2L (M/T)	100	60
3.4L	100	150
4.3L, 4.8L, 5.0L, 5.3L, 5.7L & 6.0L	100	200

RPM VARIATION LIMITS

Scheme 5

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (2.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138342-S08198199552002040800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After performing Diagnostic System Check - Engine Controls, go to next step.
Crank engine. Observe CKP Activity Counter on scan tool. Does CKP Activity Counter increment? If yes, go to next step. If no, go to step 6 .
Remove fuel pump relay with Relay Puller Pliers (J 43244). Install Spark Tester (J 26792) on cylinder No. 1 spark plug wire. Leave other 3 ignition wires connected. Crank engine and observe spark tester for spark. Repeat procedure on cylinders No. 2, 3, and 4. Do all of cylinders have spark? If yes, go to next step. If no, go to step 10 .
Turn off ignition. Inspect for malfunctioning spark plugs. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to next step.
Inspect for basic engine problems. Did you find and correct any conditions? If yes, go to step 22 . If no, see «DIAGNOSTIC AIDS»(ref-150429-S40718568222002112700000) .
Turn OFF the ignition. Disconnect ICM 2-pin connector. Turn on the ignition, with the engine off. Connect a DMM between ICM ground circuit and ICM Ignition 1 voltage circuit at connector. Does voltage measure battery voltage? If yes, go to next step. If no, go to step 17 .
Disconnect ICM 6-pin connector. Measure resistance between CKP sensor 1 signal circuit and CKP low reference circuit at connector. Does resistance measure 700-1350 ohms? If yes, go to next step. If no, go to step 11 .
With DMM still connected and set to DC Hz scale. Crank engine and observe DMM. Does frequency measure 28-32 Hz? If yes, go to next step. If no, go to step 18 .
Connect test light to battery voltage. Momentarily touch test light to low resolution engine speed signal circuit, then touch low reference circuit. Observe CKP Activity Counter on scan tool. Does CKP Activity Counter increment? If yes, go to step 13 . If no, go to step 15 .
Turn off the ignition. Disconnect PCM connectors. Connect (J 26792) to cylinder No. 1 spark plug wire, and (J 26792) to cylinder No. 2 spark plug wire. Turn on the ignition. DO NOT leave jumper wire connected to PCM IC circuit connector for longer than 5 seconds at a time. Failure to do so may damage ignition coil and/or ignition control module. Connect test light to battery voltage and momentarily touch both IC circuits at PCM connector with test light. Does spark tester spark on both wires? If yes, go to step 14 . If no, go to step 16 .
Inspect/Test CKP sensor 1 signal circuit for following conditions: Faulty connection. Open circuit. Short to ground. Short to voltage. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to next step.
Inspect/Test CKP sensor 1 low reference circuit for following conditions: Faulty connection. Open circuit. Short to ground. Short to voltage. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to step 18 .
Inspect for faulty connections at ICM. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to step 19 .
Inspect for faulty connections at PCM. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to step 21 .
Inspect/Test low resolution engine speed circuit for following conditions: Faulty connection. Open. Short to ground. Short to voltage. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to step 21 .
Test affected IC timing Control circuit for an open or a short. If a problem is found, repair condition as necessary. Did you find and correct condition? If yes, go to step 22 . If no, go to step 20 .
Repair open in battery voltage and/or ground circuit. After repairs, go to step 22 .
Replace CKP sensor. After repairs, go to step 22 .
Replace ICM. After repairs, go to step 22 .
Replace affected ignition coil. After repairs, go to step 22 .
Replace PCM. Program replacement PCM. See «POWERTRAIN CONTROL MODULE»(ref-138342-S39065537782002040800000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After repairs, go to next step.
Turn ignition OFF for 30 seconds. Start engine and operate vehicle. Observe MIL, vehicle performance, and driveability. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to step 1 .

A small amount of resistance in battery positive voltage circuit to PCM may cause a no-start. Test battery positive voltage circuit for excessive resistance or corrosion.
PCM grounds will cause a no-start only if all of them are not making a good connection.
A loose CKP sensor may cause an intermitted no-start by moving away from reluctor wheel. Inspect sensor and mating surface for being clean and tight.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (3.4L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Attempt to start engine. Does engine start and continue to run? If yes, problem is intermittent. If no, go to next step.
Disconnect 24x crank sensor. With scan tool, observe 3x crank sensor parameter and crank engine. Does scan tool indicate 3x crank sensor signal present? If yes, go to next step. If no, go to step 11 .
Reconnect 24x crank sensor. With Spark Tester (J 26792), test for spark at each cylinder. Did you observe any non-sparking cylinders? If yes, go to next step. If no, go to step 8 .
Inspect and test affected cylinder spark plug wires, ignition coils, and spark plugs for a short to ground or an arcing to ground. If carbon tracking or corrosion is present, replace both components that are affected. Did you find and correct condition? If yes, go to step 23 . If no, go to next step.
Test affected spark plug wires for proper resistance. Replace spark plug wires not near 3000 ohms per ft (9868 ohms per m). Did you find and correct condition? If yes, go to step 23 . If no, go to next step.
Switch affected cylinder coil with a known good one. If fault follows affected coil, then replace coil. Did you find and correct condition? If yes, go to step 23 . If no, go to step 15 .
Inspect spark plug wires for proper routing and for correct firing order. If any spark plug wires are found to be misrouted, reroute as necessary. Did you find and correct condition? If yes, go to step 23 . If no, go to next step.
With DMM, test spark plugs for internal short to ground. Replace any grounded spark plugs that are found. Did you find and correct condition? If yes, go to step 23 . If no, go to next step.
Remove spark plugs. Inspect spark plugs for damage. If any spark plugs are found to be bad, replace affected spark plugs. After repairs, go to step 23 .
Reconnect 24x crank sensor. Disconnect IC module connectors. Turn ON the ignition. With test light that is connected to a good ground, probe IC module Ignition 1 voltage circuit. Does test light illuminate? If yes, go to next step. If no, go to step 17 .
Connect test light between IC module Ignition 1 voltage circuit and IC module ground circuit. Does test light illuminate? If yes, go to next step. If no, go to step 20 .
Disconnect 7x crankshaft sensor connector from IC module. With test light connected to battery voltage, probe both CKP sensor 1 signal 7x and low reference 7x circuits. Does test light illuminate when probing either circuits? If yes, go to step 18 . If no, go to next step.
Connect test light to ground. Probe CKP sensor 1 signal 7x and reference low 7x circuits. Does test light illuminate when probing either circuit? If yes, go to step 19 . If no, go to next step.
Ensure battery voltage is within specifications. Turn off the ignition. Connect DMM between CKP sensor 1 signal circuit 7x and low reference 7x circuit at IC module harness connector. Crank engine while observing AC duty cycle percent. Does DMM indicate AC duty cycle is present? If yes, go to step 21 . If no, go to next step.
Test 7x crank sensor circuits for the following conditions: Opens. CKP sensor 1 signal and low reference 7x circuits are shorted together. Repair any damaged wiring. Did you find and correct condition? If yes, go to step 23 . If no, go to step 22 .
Repair open or short to ground in IC module Ignition 1 voltage circuit. Replace fuse if necessary. After repairs, go to step 23 .
Repair short to ground in circuit which illuminated test light. After repairs, go to step 23 .
Repair short to voltage in circuit which illuminated test light. After repairs, go to step 23 .
Repair open in IC module ground circuit. After repairs, go to step 23 .
Replace IC module. After repairs, go to step 23 .
Replace 7x crank sensor. After repairs, go to next step.
Remove all test equipment. Connect any disconnected components or any disconnected fuses. Turn the ignition OFF for 30 seconds. Start engine and operate. Observe MIL, vehicle performance, and driveability. Does vehicle operate correctly, without any MIL illumination and without any stored DTCs? If yes, system is okay. If no, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (4.2L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-132531-S16910731432002012100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
Are DTCs P0335 or P0336 set? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-132531-S07878208602002012100000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. If no, go to next step.
Attempt to start engine. Does engine start and run? If yes, go to next step. If no, go to step 15 .
Observe Misfire Current Counters parameter with scan tool. Does scan tool display any Misfire Current Counters incrementing? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(ref-150429-S01159227462002120300000) .
Remove ignition coil for affected cylinder. Install Spark Tester (J 26792) to spark plug boot. Attach clamp end of (J 26792) to a good engine ground. Observe (J 26792). Crank engine. Does spark jump tester gap? If yes, go to step 11 . If no, go to next step.
Turn OFF the ignition. Disconnect ignition coil for misfiring cylinder. Turn ON the ignition, with the engine OFF. Probe Ignition 1 voltage circuit of affected ignition coil with test light connected to good ground. Does test light illuminate? If yes, go to next step. If no, go to step 15 .
Probe Ignition 1 voltage circuit of affected ignition coil with test light connected to ignition coil ground circuit. Does test light illuminate? If yes, go to next step. If no, go to step 16 .
Start engine. Measure frequency from IC Control circuit of respective ignition coil to a good ground. Does frequency measure within 2-20 Hz? If yes, go to step 14 . If no, go to next step.
Turn ON the ignition, with engine OFF. Measure voltage from IC Control circuit of respective ignition coil to a good ground with DMM. Does voltage measure more than one volt? If yes, go to step 17 . If no, go to next step.
Test IC Control circuit for an open, a short to ground or high resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 13 .
Exchange spark plug with a spark plug from a non-misfiring cylinder. Install ignition coil. Start engine. Does scan tool display that misfire followed that spark plug? If yes, go to step 20 . If no, go to next step.
Inspect insulating spark plug boot and conducting spring for contamination, deterioration or any arching. Did you find and correct the condition? If yes, go to step 21 . If no, check for base engine mechanical faults. See appropriate TROUBLE SHOOTING article in ENGINES.
Test for an intermittent and for a poor connection at PCM. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 19 .
Test for an intermittent and for a poor connection at ignition coil. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
Repair open or short to ground in Ignition 1 voltage circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 21
Repair open in ignition coil ground circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 21
Repair short to voltage in IC Control circuit. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 21
Replace ignition coil. After repairs, go to step 21
Replace PCM. Program replacement PCM. See «POWERTRAIN CONTROL MODULE»(ref-132531-S15401290812002012100000) under PROGRAMMING in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article. After repairs, go to step 21
Replace spark plug. After repairs, go to next step.
Attempt to start engine. Does engine start and run? If yes, go to next step. If no, go to step 2 .
Clear DTCs with scan tool. Turn OFF the ignition for 30 seconds. Start engine. Let engine reach operating temperature. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-132531-S07878208602002012100000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article.

Crankshaft Position (CKP) signal is not needed to start and run.
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Inspect PCM and engine grounds for clean and secure connections.
For intermittent conditions, see «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (4.3L, 5.0L & 5.7L)

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Crank engine. Observe Engine Speed parameter with scan tool. Does scan tool display engine RPM? If yes, go to next step. If no, go to step 19 .
Check spark plug wires for open circuits, cracks, or improper seating of terminals at spark plugs, distributor, and ignition coil before proceeding with test. Check spark at plug with Spark Tester (J 26792) or equivalent while cranking. If there is no spark on one wire, check a second wire. A few sparks then nothing is considered no spark. Does spark occur on all cylinders? If yes, condition is intermittent. If no, go to next step.
Remove coil wire from distributor cap. Insert (J 26792) into coil wire and clamp tester onto a ground. Crank engine. Does spark occur? If yes, go to step 13 . If no, go to next step.
Measure coil wire resistance. Does resistance measure approximately 1000 ohms/inch? If yes, go to next step. If no, go to step 32 .
Disconnect ignition coil harness connector. Probe harness ignition coil driver circuit with test light connected to battery positive voltage. Crank engine. Does test light flash while cranking engine? If yes, go to step 8 . If no, go to next step.
Turn OFF the ignition. Probe harness ignition coil driver circuit with test light connected to battery positive voltage. Does test light illuminate? If yes, go to step 29 . If no, go to step 9 .
Turn ON the ignition, with the engine OFF. Measure coil Ignition 1 voltage with DMM connected to a ground. Does voltage measure above 10 volts? If yes, go to step 22 . If no, go to step 18 .
Turn OFF the ignition. Check for an open circuit between ignition coil and ICM. Did you find the condition? If yes, go to step 28 . If no, go to next step.
Turn ON the ignition, with the engine OFF. Measure Ignition 1 voltage at ICM harness connector with DMM connected to a ground. Does voltage measure above 10 volts? If yes, go to next step. If no, go to step 20 .
Probe ICM harness connector ground circuit with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 24 .
Probe IC timing Control circuit with DMM set to AC scale connected to a ground. Crank engine. Observe voltage while engine is being cranked. Does voltage measure 1-4 volts? If yes, go to step 21 . If no, go to step 15 .
Remove distributor cap. Check cap for the following conditions: Cracks. Moisture. Carbon tracks. Physical damage. Did you find any of these conditions? If yes, go to step 34 . If no, go to next step.
Crank engine. Observe distributor rotor while engine is being cranked. Did rotor turn? If yes, go to step 33 . If no, repair engine mechanical problem. See appropriate article in ENGINES.
Turn OFF the ignition. Disconnect PCM. Check ignition timing Control circuit for an open between PCM and ICM. Did you find the condition? If yes, go to step 25 . If no, go to next step.
Probe ignition timing Control circuit at PCM with test light connected to battery voltage. Does test light illuminate? If yes, go to step 26 . If no, go to next step.
Turn ON the ignition, with the engine OFF. Probe ignition timing Control circuit at PCM with test light connected to ground. Does test light illuminate? If yes, go to step 27 . If no, go to step 23 .
Check for an open or shorted to ground Ignition 1 voltage circuit at ignition coil. Repair as necessary. After repairs, go to step 37 .
Check for a short to ground on CKP or CMP 12-volt reference circuit. Repair as necessary. Did you find and correct the condition? If yes, go to step 37 . If no, go to step 36 .
Check for an open or a short to ground on Ignition 1 voltage circuit at ICM. Repair as necessary. After repairs, go to step 37 .
Check for poor ICM connection. Did you find a problem? If yes, go to step 30 . If no, go to step 35 .
Check for poor coil connection. Did you find a problem? If yes, go to step 30 . If no, go to step 31 .
Check for poor PCM connection. Did you find a problem? If yes, go to step 30 . If no, go to step 30 .
Repair open ICM ground circuit. After repairs, go to step 37 .
Repair open ignition timing Control circuit. After repairs, go to step 37 .
Repair grounded ignition timing Control circuit. After repairs, go to step 37 .
Repair short to voltage in ignition timing Control circuit. After repairs, go to step 37 .
Repair open in coil driver circuit between ignition coil and ICM. After repairs, go to step 37 .
Repair short to ground in coil driver circuit between ignition coil and ICM. After repairs, go to step 37 .
Repair circuit as necessary. After repairs, go to step 37 .
Replace ignition coil. After repairs, go to step 37 .
Replace coil wire. After repairs, go to step 37 .
Replace distributor rotor. After repairs, go to step 37 .
Replace distributor cap. After repairs, go to step 37 .
Replace ICM. After repairs, go to step 37 .
Replace PCM. Program replacement PCM. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
Operate vehicle within conditions under which original symptom was noted. Does system now operate properly? If yes, system is okay. If no, go to step 1 .

Check for the following when distributor rotor does not rotate while engine is cranking

A broken distributor drive shaft.
A worn distributor drive gear or camshaft timing chain and gears.

An intermittent may be caused by any of the following conditions

A poor connection.
Rubbed through wire insulation.
A broken wire inside insulation.

Thoroughly inspect any circuitry that is suspected of causing intermittent complaint.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (4.8L, 5.3L, 6.0L & 8.1L)

Note. For component locations, see COMPONENT LOCATIONS .

The electronic ignition system uses an individual ignition coil for each cylinder. Powertrain Control Module (PCM) controls ignition operation through 8 individual Ignition Control (IC) circuits. Each bank of 4 ignition coils is connected to PCM, power, or ground by the following circuits

Low Reference
Chassis Ground
Ignition 1 Voltage
Appropriate IC Circuit

PCM triggers an ignition coil by grounding appropriate IC circuit using information from Crankshaft Position (CKP) and Camshaft Position (CMP) sensors.

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Crank the engine. Use a scan tool in order to observe engine speed parameter. Does scan tool display engine RPM? If yes, go to next step. If no, go to step 25 .
Are DTCs P0335, P0336, or P0351-P0358 set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
Install scan tool. Idle engine. Use a scan tool in order to monitor all Misfire Current counters on misfire data list. Do any of Misfire Current counters increment? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(ref-150429-S35471253432002112700000) .
Do misfire current counters increment for most cylinders on one bank of engine? If yes, go to step 11 . If no, go to next step.
Inspect spark plug wire for open circuits, cracks, or improper seating of terminals at spark plug or coil before proceeding with test. Inspect for spark at plug with Spark Tester (J 26792) while cranking. Is adequate spark present? If yes, go to step 31 . If no, go to next step.
Measure spark plug wire resistance. Does resistance measure near 460-720 ohms/ft? If yes, go to next step. If no, go to step 30 .
Turn OFF the ignition. Disconnect ignition coil electrical harness connector that corresponds to Misfire Current counter that was incrementing. Turn ON the ignition, with the engine OFF. Probe Ignition 1 voltage circuit at ignition coil electrical connector with test light connected to battery ground. Does test light illuminate? If yes, go to next step. If no, go to step 13 .
Probe Ignition 1 voltage circuit at ignition coil electrical connector to ignition coil ground circuit with test light. Does test light illuminate? If yes, go to next step. If no, go to step 16 .
Probe Ignition 1 voltage circuit at ignition coil electrical connector to ignition coil low reference circuit with test light. Does test light illuminate? If yes, go to step 24 . If no, go to step 20 .
Inspect for an open ignition coil fuse. Locate and repair Ignition 1 voltage circuit for a grounded circuit if fuse is open. See «WIRING DIAGRAMS»(ref-142952) article. Replace fuse. Did you find and correct the condition? If yes, go to step 34 . If no, go to next step.
Repair open in Ignition 1 voltage circuit between fuse block and splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Disconnect main ignition coil 8-way connector. Probe Ignition 1 voltage circuit at ignition coil main 8-way connector using test light connected to battery ground. Does test light illuminate? If yes, go to next step. If no, go to step 15 .
Repair open Ignition 1 voltage circuit between splice and ignition coil connector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Repair open Ignition 1 voltage circuit between fuse block fuse and splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Disconnect main ignition coil 8-way connector. Probe coil Ignition 1 voltage circuit to ignition coil ground circuit at ignition coil main electrical 8-way connector using test light connected to battery ground. Does test light illuminate? If yes, go to next step. If no, go to step 19 .
Inspect for a poor connection at main ignition coil 8-way electrical connector. Repair poor connections as necessary. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 34 . If no, go to next step.
Repair open ground circuit between main 8-way connector and ignition coil connector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Repair open ground circuit between ground and main 8-way connector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Disconnect main ignition coil 8-way connector. Probe Ignition 1 voltage circuit at ignition coil main electrical 8-way connector to ignition coil low reference circuit using test light. Does test light illuminate? If yes, go to next step. If no, go to step 23 .
Inspect for a poor connection at main ignition coil electrical 8-way connector. If a poor connection is found, repair as necessary. Did you find and correct the condition? If yes, go to step 34 . If no, go to next step.
Repair open low reference circuit between main 8-way connector and ignition coil connector. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Repair open low reference circuit between PCM and splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 34 .
Inspect for poor connections at ignition coil harness connector. Repair poor connections as necessary. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 29 .
Turn ON the ignition, with the engine OFF. Disconnect CKP sensor harness connector. Measure voltage from CKP sensor 12-volt reference circuit and a good ground using DMM. Is voltage near battery voltage? If yes, go to next step. If no, go to step 28 .
Inspect for poor connections at CKP sensor. Did you find and correct the condition? If yes, go to step 34 . If no, go to next step.
Replace CKP sensor. After repairs, go to step 34 .
Test for a short to ground in CKP sensor 12-volt reference circuit and CMP sensor 12-volt reference circuit. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 32 .
Replace ignition coil. After repairs, go to step 34 .
Replace spark plug wire. After repairs, go to step 34 .
Replace spark plug. After repairs, go to step 34 .
Inspect for poor connections at PCM. Did you find and correct the condition? If yes, go to step 34 . If no, go to next step.
Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to step 34 .
Attempt to start engine. Does engine start and continue to run? If yes, go to next step. If no, go to step 2 .
Turn OFF engine for 30 seconds. Start engine and operate vehicle. Observe MIL, vehicle performance, and driveability. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article.

Note. A missing CMP sensor signal may cause a long crank condition. CKP signal must be available for engine to start. CMP signal is not needed to start and operate engine. PCM can determine when a cylinder is on either firing or exhaust stroke by the 24x signal.

Note. On 8.1L, 12-volt reference circuit for CKP and CMP sensors are shared internally in PCM.

Note. Remove any debris from PCM connector surfaces before servicing PCM. Inspect PCM connector gaskets when diagnosing or replacing PCM. Ensure gaskets are installed correctly. Gaskets prevent water intrusion into PCM.

For an intermittent condition, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.

IGNITION RELAY DIAGNOSIS (3.4L)

Note. For component locations, see COMPONENT LOCATIONS .

Ignition relay supplies battery positive voltage to ignition control module, fuel injectors, Mass Air Flow (MAF) sensor, oxygen sensor, transmission solenoids and A/C clutch relay.

The following will occur if ignition relay fails to close

The engine will crank, but does not run.
Scan tool data will be available.
Instrument panel lights will illuminate.

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn OFF the ignition. Remove underhood fuse block cover. Remove ignition relay with Relay Puller Pliers (J 43244). Probe battery positive voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. if no, go to step 10 .
Turn ON the ignition, with the engine OFF. Probe Ignition 1 voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 6 .
Turn ON the ignition, with the engine OFF. Probe coil ground circuit for ignition relay at underhood fuse block with test light connected to 12 volts. Does test light illuminate? If yes, go to next step. If yes, go to step 7 .
Turn OFF the ignition. Jumper ignition relay battery positive voltage circuit and ignition relay load circuit together using fused jumper wire. Probe Engine Controls, FUEL INJ and O2 Sensor fuses with test light connected to ground. Does test light illuminate for all fuses? If yes, go to step 8 . If no, go to step 10 .
Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test Ignition 1 voltage circuit of ignition relay at underhood fuse block electrical connector for an open circuit or for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test coil ground circuit of ignition relay at underhood fuse block electrical connector for a high resistance or for an open circuit. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
Inspect for poor terminal contact at ignition relay underhood electrical center connector. Did you find and correct condition? If yes, go to step 10 . If no, go to next step.
Replace ignition relay. After repairs, go to step 11 .
Replace underhood electrical center. After repairs, go to next step.
Remove all test equipment. Connect any disconnected components, fuses, etc. Turn ignition OFF for 30 seconds. Start engine and operate vehicle. Observe Malfunction Indicator Light (MIL), vehicle performance and driveability. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) or «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) article.

IGNITION RELAY DIAGNOSIS (4.3L)

Note. For component locations, see COMPONENT LOCATIONS .

Ignition relay supplies ignition voltage to fuel injectors, ignition coils, Powertrain Control Module (PCM) and alternator/generator.

If IGN relay fails to close

Scan data will be available.
Vehicle will crank, no start.
Dash indicator lights will illuminate.

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn OFF the ignition. Remove underhood electrical center cover. Remove IGN relay. Probe IGN relay battery positive voltage circuit at underhood electrical center terminal with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 8 .
Turn ON the ignition, with the engine OFF. Probe IGN relay Ignition 1 voltage circuit at underhood electrical center with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 9 .
Turn ON the ignition, with the engine OFF. Probe ignition main relay ground connector terminal with test light connected to 12 volts. Does test light illuminate? If yes, go to next step. If no, go to step 10 .
Turn OFF the ignition. Jumper IGN relay battery positive voltage circuit and IGN relay load circuit together using fused jumper wire. Probe ECM I, INJR A and INJR B fuses with test light connected to ground. Does test light illuminate for all fuses? If yes, go to next step. If no, go to step 10 .
Inspect for poor terminal contact at IGN relay underhood electrical center connector. Did you find and correct condition? If yes, go to step 11 . If no, go to next step.
Replace IGN relay. After repairs, go to step 11 .
Repair open or short to ground in battery positive voltage supply to IGN relay. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 11 .
Repair Ignition 1 voltage circuit to IGN relay. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 11 .
Replace underhood electrical center. After repairs, go to next step.
Remove all test equipment except scan tool. Reconnect any disconnected components, fuses, etc. Turn ignition OFF for 30 seconds. Start engine and operate vehicle. Observe Malfunction Indicator Light (MIL), vehicle performance, and driveability. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in «SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP»(ref-137937) , «SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA»(ref-137808) or «SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO»(ref-132892) article.

IGNITION RELAY DIAGNOSIS (4.8L, 5.3L & 6.0L)

Note. For component locations, see COMPONENT LOCATIONS .

Ignition relay supplies ignition voltage to fuel injectors, ignition coils, Powertrain Control Module (PCM) and Throttle Actuator Control (TAC) module.

The following will occur if ignition relay fails to close

The engine cranks, but does not run.
Scan tool data will be available.
Instrument panel lights will illuminate.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138163-S11395166402002032500000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn OFF the ignition. Remove underhood fuse block cover. Remove ignition relay with Relay Puller Pliers (J 43244). Probe battery positive voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. if no, go to step 10 .
Turn ON the ignition, with the engine OFF. Probe Ignition 1 voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 6 .
Turn ON the ignition, with the engine OFF. Probe coil ground circuit for ignition relay at underhood fuse block with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If yes, go to step 7 .
Turn OFF the ignition. Jumper IGN relay battery positive voltage circuit and IGN relay load circuit together using fused jumper wire. Probe ECM I, INJ A and INJ B fuses with test light connected to ground. Does test light illuminate for all fuses? If yes, go to step 8 . If no, go to step 10 .
Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test Ignition 1 voltage circuit of ignition relay at underhood fuse block electrical connector for an open circuit or for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test coil ground circuit of ignition relay at underhood fuse block electrical connector for a high resistance or for an open circuit. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
Inspect for poor terminal contact at ignition relay underhood electrical center connector. Did you find and correct condition? If yes, go to step 10 . If no, go to next step.
Replace ignition relay. After repairs, go to step 11 .
Replace underhood electrical center. After repairs, go to next step.
Clear DTCs with scan tool. Turn ignition OFF for 30 seconds. Start engine. Operate vehicle for 5 minutes. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138163-S13555095322002032500000) in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article.

IGNITION RELAY DIAGNOSIS (5.7L BI-FUEL)

Note. For component locations, see COMPONENT LOCATIONS .

The ignition relay is the positive voltage supply source for the following components

Fuel gauge select switch.
Lock-off relay.
Idle control solenoid.
Fuel control solenoid.
Low pressure lock-off solenoid.

The ignition relay coil is energized when ignition switch is turned to RUN or START positions. The ignition relay switch contact is supplied voltage at all times.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138305-S37770098362002040400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
Turn the ignition ON, with the engine OFF. Inspect CNG, ECM 1 and TRANS fuses. Is any fuse open? If yes, go to step 15 . If no, go to next step.
Probe both terminals of each fuse using Test Light (J 34142-B) connected to a known good ground. Ensure that ignition is ON and engine is OFF. With fuses installed, the probe test points for fuses are visible at either side of amperage rating. Does test light illuminate at all terminals? If yes, go to step 5 . If no, go to next step.
Inspect fuse terminal contact. Repair fuse terminal contact as necessary. Test fuse supply source. Typically, source is a MAXI fuse, fusible link or a relay. Repair fuse supply source as necessary. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Using scan tool, attempt to communicate and retrieve data from AF ECM. Does scan tool display Alternative Fuels ECM data? If yes, go to step 8 . If no, go to next step.
Turn the ignition OFF. Disconnect AF ECM connectors. Turn the ignition ON leaving the engine OFF. Probe battery power and ignition power circuit terminals at AF ECM connectors with (J 34142-B) connected to a known good ground. Does test light illuminate at all terminals? If yes, go to next step. If no, go to step 16 .
Probe all AF ECM ground circuit terminals at ECM connector with (J 34142-B) connected to battery positive. Does test light illuminate at all terminals? If yes, go to step 22 . If no, go to step 16 .
Observe fuel gauge select switch data parameter on scan tool. Depress and release fuel gauge select switch. Did fuel gauge select switch data parameter indicate APPLIED when switch was depressed? If yes, go to step 10 . If no, go to next step.
With the ignition ON, backprobe ignition relay switch load terminal No. 87 with (J 34142-B) connected to a known good ground. Is test light illuminated? If yes, go to FUEL GAUGE RELAY DIAGNOSIS - ALTERNATIVE FUELS in appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If no, go to step 12 .
Observe Alternative Fuels engine speed data parameter on scan tool. Observe engine speed parameter as you crank and attempt to start engine. Is engine RPM displayed as you crank or start engine? If yes, go to next step. If no, go to «DTC P0336: CRANKSHAFT POSITION (CKP) SENSOR PERFORMANCE»(ref-150916-S13735874082002112700000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA article.
With the ignition ON, backprobe ignition relay switch load terminal No. 87 with (J 34142-B) connected to a known good ground. Observe test light as you turn ignition OFF. Is test light illuminated with ignition OFF? If yes, go to step 17 . If no, system is okay.
With the ignition ON, backprobe ignition relay switch supply terminal No. 30 with (J 34142-B) connected to a known good ground. Is test light illuminated? If yes, go to next step. If no, go to step 18 .
With the ignition ON, backprobe ignition relay coil supply terminal No. 85 with (J 34142-B) connected to a known good ground. Is test light illuminated? If yes, go to next step. If no, go to step 19 .
Disconnect ignition relay connector. With ignition on, connect (J 34142-B) between ignition relay coil supply terminal No. 85 and ignition relay coil ground terminal No. 86. Is test light illuminated? If yes, go to step 21 . If no, go to step 20 .
Test for short that caused fuse to open. Possible shorts include the following: CNG Fuse A shorted fuel gauge select switch circuit. A shorted lock-off or fuel solenoid or circuit. A shorted AF ECM or AF ECM battery power circuit. ECM 1 Fuse A shorted ignition relay coil or circuit. A shorted base vehicle circuit. See POWER DISTRIBUTION article in WIRING DIAGRAMS. TRANS Fuse A shorted AF ECM or AF ECM ignition power circuit. A shorted base vehicle circuit. See POWER DISTRIBUTION article in WIRING DIAGRAMS. Repair circuits or replace components as necessary. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Repair open in AF ECM circuit that did not illuminate test light. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Replace stuck ignition relay or repair ignition power circuit shorted to battery positive. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Repair open in ignition relay switch supply circuit between relay and circuit splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Repair open in ignition relay coil supply circuit between relay and circuit splice. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Repair open in ignition relay coil ground circuit between relay and ground. See «WIRING DIAGRAMS»(ref-142952) article. After repairs, go to step 24 .
Replace ignition relay. After repairs, go to step 24 .
Inspect for proper AF ECM terminal contact. Test for an open Class 2 serial data circuit between splice and AF ECM connector terminal. See «WIRING DIAGRAMS»(ref-142952) article. Repair terminal contact or wiring as necessary. Was terminal contact or a wiring repair performed? If yes, go to step 24 . If no, go to next step.
Replace AF ECM. Program replacement AF ECM. See «ALTERNATIVE FUEL ENGINE CONTROL MODULE»(ref-150916-S08120108542002112700000) under PROGRAMMING in SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA - BI-FUEL article. After repairs, go to next step.
Remove all test equipment except scan tool. Connect any disconnected components, fuses, etc. Using scan tool, clear DTC information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe Fuel Indicator Light (FIL) and MIL. Observe vehicle performance and driveability. After operating vehicle, inspect BOTH control modules for stored DTCs. Does vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs? If yes, system is okay. If no, perform «ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-150916-S24618652742002112700000) under SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA - BI-FUEL article.

IGNITION RELAY DIAGNOSIS (8.1L)

Note. For component locations, see COMPONENT LOCATIONS .

Ignition relay supplies ignition voltage to fuel injectors, ignition coils, Powertrain Control Module (PCM) and Throttle Actuator Control (TAC) module.

The following will occur if ignition relay fails to close

The engine cranks, but does not run.
Scan tool data will be available.
Instrument panel lights will illuminate.

Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138305-S37770098362002040400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
Turn OFF the ignition. Remove underhood fuse block cover. Remove ignition relay with Relay Puller Pliers (J 43244). Probe battery positive voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. if no, go to step 10 .
Turn ON the ignition, with the engine OFF. Probe Ignition 1 voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step 6 .
Turn ON the ignition, with the engine OFF. Probe coil ground circuit for ignition relay at underhood fuse block with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 7 .
Turn OFF the ignition. Jumper IGN relay battery positive voltage circuit and IGN relay load circuit together using fused jumper wire. Probe ECM I, INJ A and INJ B fuses with test light connected to ground. Does test light illuminate for all fuses? If yes, go to step 8 . If no, go to step 10 .
Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test Ignition 1 voltage circuit of ignition relay at underhood fuse block electrical connector for an open circuit or for a short to ground. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test coil ground circuit of ignition relay at underhood fuse block electrical connector for a high resistance or for an open circuit. See «WIRING DIAGRAMS»(ref-142952) article. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
Inspect for poor terminal contact at ignition relay underhood electrical center connector. Did you find and correct condition? If yes, go to step 10 . If no, go to next step.
Replace ignition relay. After repairs, go to step 11 .
Replace underhood electrical center. After repairs, go to next step.
Clear DTCs with scan tool. Turn ignition OFF for 30 seconds. Start engine. Operate vehicle for 5 minutes. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138305-S40253083952002040400000) in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article.

EVAP Control System Diagnosis

Note. The following procedure does not apply to 2.2L or 3.0L Saturn.

For EVAP control system diagnosis, see appropriate INSPECTION/MAINTENANCE PROCEDURES in appropriate SELF-DIAGNOSTICS article.

Inspection Procedure

Note. DO NOT perform this procedure unless instructed by EVAP diagnostic test.

Note. Use EVAP Pressure/Purge Diagnostic Station (J 41413) in order to provide a clean, dry, low pressure gas source. DO NOT substitute any other pressurized gas source. Damage may result to EVAP system.

Turn OFF the ignition.
Remove EVAP canister purge valve.
Lightly tap EVAP canister purge valve on a hard surface.
Inspect for carbon particles exiting either vacuum port. If no carbon particles were detected, install original EVAP canister purge valve and continue with cleaning procedure. If carbon particles are found during inspection procedure, replace EVAP canister purge valve and continue with cleaning procedure. If you were instructed to replace EVAP canister purge valve and no carbon particles are found, return to EVAP diagnostic procedure that directed you here. DO NOT perform EVAP cleaning procedure.

FUEL TANK LEAK TEST

Note. For component locations, see COMPONENT LOCATIONS .

Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
Raise vehicle. Inspect fuel tank and fuel pipes for damage or external leaks. Did you find fuel leaking from fuel tank? If yes, go to step 7 . If no, go to next step.
Turn ON the ignition, with the engine OFF. With scan tool, command fuel pump ON. Inspect for fuel leaking from fuel pipes. Did fuel leak from fuel pipes? If yes, go to step 8 . If no, go to next step.
Install Fuel Tank Cap Adapter (J 41415-40). Connect EVAP Pressure/Purge Diagnostic Station (J 41413) to fuel tank cap adapter. With scan tool, seal EVAP system. DO NOT exceed 15 in. H 2 O. With EVAP pressure/purge diagnostic station, pressurize fuel tank. Did fuel leak from fuel tank? If yes, go to step 7 . If no, go to next step.
With EVAP pressure/purge diagnostic station, maintain pressure in fuel tank. With Ultrasonic Leak Detector (J 41416), test for leaks above fuel level in following locations: Fuel tank, fill limiter vent valve, pressure relief valve and rollover valves. Fuel sender housing and fuel sender seal. Fuel Tank Pressure (FTP) sensor seal. EVAP vapor pipes. Fuel fill pipe and hose. Did you locate a fuel leak? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-150429-S05061006802002112700000) .
Repair system as necessary. After repairs, system is okay.
Replace fuel tank. After repairs, system is okay.
Replace leaking fuel pipe. After repairs, system is okay.

Operate vehicle under condition of customer's concern. Under high temperature conditions fuel vapors may increase to point of EVAP canister vapor saturation. Fuel vapors would then be released into atmosphere. Once engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
Test for fuel leaking in fuel tank, rear tank if equipped, and fuel feed and return pipes.
Test for fuel vapor leaks in fuel tank, fill limiter vent valve and rollover valves, fuel fill pipe, hose and fuel fill cap, fuel sender housing and seal, Fuel Tank Pressure (FTP) sensor seal and EVAP vapor pipe.
Movement of EVAP pipes or fuel pipes may help find an intermittent condition.

Operate engine until it reaches normal operating temperature.
Disconnect engine vacuum harness from vacuum pump inlet pipe.
Connect Valve Manometer (J 23951), or vacuum gauge, to vacuum pump inlet pipe.
Operate engine at an idle for 30 seconds. If engine operates for longer than 30 seconds, or if engine does not operate at an idle, vent manometer and repeat this step.
While operating engine, observe manometer reading. Reading should be within specification. See «VACUUM PUMP SPECIFICATIONS»(ref-150429-S24698802162002120200000) table. VACUUM PUMP SPECIFICATIONS Elevation - Ft. Minimum Specification - In. H 2 O (kPa) Zero 21 (-70) 5000 18 (-60) 10,000 14 (-49) 15,000 12 (-40)
If vacuum pump fails to meet minimum specifications, replace vacuum pump and retest

Engine Controls - System & Component Testing: Diagnosis Chevrolet Tahoe II

Diagnostic Procedures

Diagnostic Aids

Diagnostic Procedure

FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)

Circuit Description

FUEL INJECTOR CIRCUIT DIAGNOSIS (BI-FUEL & CNG)

FUEL INJECTOR COIL TEST (BI-FUEL & CNG)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL

FUEL INJECTOR BALANCE TEST WITH TECH 2

FUEL HEATER INOPERATIVE DIAGNOSIS (6.5L)

FUEL HEATER ALWAYS ON DIAGNOSIS (6.6L)

FUEL HEATER INOPERATIVE DIAGNOSIS (6.6L)

FUEL INJECTION NOZZLE DIAGNOSIS (6.5L)

Injector Balance Test

Nozzle Opening Pressure Test

Nozzle Leak Test

FUEL INJECTOR BALANCE TEST WITH TECH 2 (6.6L)

FUEL RETURN SYSTEM DIAGNOSIS (6.6L)

FUEL SYSTEM DIAGNOSIS - CAB & CHASSIS (6.6L)

FUEL SYSTEM DIAGNOSIS - PICKUP (6.6L)

FUEL SYSTEM DIAGNOSIS - HIGH PRESSURE SIDE (6.6L)

GLOW PLUG SYSTEM DIAGNOSIS (6.5L)

GLOW PLUG SYSTEM DIAGNOSIS (6.6L)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (2.2L SONOMA & S10 PICKUP)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (3.4L)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.2L)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.3L VIN W & X)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (4.8L, 5.3L & 6.0L)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (5.0L & 5.7L)

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL (8.1L)

FUEL INJECTOR BALANCE TEST WITH TECH 2 (2.2L SONOMA & S10 PICKUP)

FUEL INJECTOR BALANCE TEST WITH TECH 2 (3.4L)

FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.2L)

FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.3L VIN W & X)

FUEL INJECTOR BALANCE TEST WITH TECH 2 (4.8L, 5.3L & 6.0L)

FUEL INJECTOR BALANCE TEST WITH TECH 2 (8.1L)

FUEL INJECTOR CIRCUIT DIAGNOSIS (2.2L)

FUEL INJECTOR CIRCUIT DIAGNOSIS (4.2L)

FUEL INJECTOR CIRCUIT DIAGNOSIS (4.3L)

FUEL INJECTOR COIL TEST (2.2L SONOMA & S10 PICKUP)

FUEL INJECTOR COIL TEST (3.4L)

FUEL INJECTOR COIL TEST (4.2L)

FUEL INJECTOR COIL TEST (4.3L VIN W & X)

FUEL INJECTOR COIL TEST (4.8L, 5.3L & 6.0L)

FUEL INJECTOR COIL TEST (5.0L & 5.7L)

FUEL INJECTOR COIL TEST (8.1L)

FUEL SYSTEM PRESSURE TEST

IDLE AIR CONTROL SYSTEM DIAGNOSIS

Scheme 5

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (2.2L)

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (3.4L)

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (4.2L)

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (4.3L, 5.0L & 5.7L)

ELECTRONIC IGNITION SYSTEM DIAGNOSIS (4.8L, 5.3L, 6.0L & 8.1L)

IGNITION RELAY DIAGNOSIS (3.4L)

IGNITION RELAY DIAGNOSIS (4.3L)

IGNITION RELAY DIAGNOSIS (4.8L, 5.3L & 6.0L)

IGNITION RELAY DIAGNOSIS (5.7L BI-FUEL)

IGNITION RELAY DIAGNOSIS (8.1L)

EVAP Control System Diagnosis

Inspection Procedure

FUEL TANK LEAK TEST

More articles — Engine Controls - System & Component Testing

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