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

MODEL IDENTIFICATION

Note. Component locations are available for all models. See COMPONENT LOCATIONS .

Vehicle model is identified by fifth character of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

MODEL IDENTIFICATION

Description

The manifold absolute pressure (MAP) sensor responds to pressure changes in the intake manifold which gives an indication of the engine load. The MAP sensor has the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low signal voltage. With high MAP such as ignition ON, with the engine OFF or Wide Open Throttle (WOT), the PCM should detect a high signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set. IF the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

Test Description

The number below refers to the step number in the diagnostic procedures.

1. 2 This step tests the MAP sensor's ability to correctly indicate BARO. The BARO varies with altitude and atmospheric conditions. 103 kPa is the approximate BARO displayed by the MAP sensor at or near sea level.

System Description

Alternative Fuel (AF) fuel pump relay coil is supplied power when ignition is in RUN and START position. Alternative Fuels Engine Control Module (AF ECM) supplies ground path to AF fuel pump relay coil when engine starts and runs on CNG. The purpose of AF fuel pump relay circuitry is to allow AF ECM the ability to turn OFF gasoline fuel pump and to supply a voltage source for lock-off relay. At initial ignition ON, AF fuel pump relay is not energized by AF ECM. The gasoline Powertrain Control Module (PCM) energizes gasoline fuel pump relay, supplying power to Fuel Pump Relay Control circuit for a 2 second prime pulse. When prime pulse is supplied to Fuel Pump Relay Control circuit, lock-off relay is energized and gasoline fuel pump relay receives the 2 second prime pulse power. The 2 second prime pulse is for gasoline fuel pump durability purposes. When engine is operating on CNG, AF ECM energizes AF fuel pump relay in order to turn OFF gasoline fuel pump. The lock-off relay continues to be energized by PCM gasoline Fuel Pump Relay Control circuit.

The numbers below refer to step numbers in diagnostic procedures.

1. 1 System Check must be performed before proceeding with diagnostic procedures. Failure to perform System Check will result in misdiagnosis.
2. 3 The scan tool will command PCM to turn ON fuel pump and AF ECM to turn OFF AF fuel pump relay.
3. 4 Fuel pump prime terminal is located in underhood fuse block.
4. 5 Lock-off solenoid relay is controlled by PCM Fuel Pump Relay Control circuit.

Alternative Fuel Engine Control Module (AF ECM) controls fuel system when vehicle is operating on CNG. CNG is stored in a tank at pressures up to 3600 psi. A High Pressure Lock-Off (HPL) solenoid located in the tank and a Low Pressure Lock-Off (LPL) located in fuel line, prevent fuel flow. When ignition is turned on, AF ECM commands HPL open for one second to charge fuel system, and allows Fuel Pressure Sensor (FPS) to monitor tank pressure. When engine is cranking or running, AF ECM opens both HPL and LPL. This fuel delivery system utilizes 2 different pressure stages in order to lower fuel pressure from tank pressure down to an injector delivery pressure.

1. High Pressure Regulator Stage When AF ECM commands HPL solenoid open, fuel begins to flow through High Pressure Regulator (HPR). HPR reduces fuel pressure to 110-210 psi (758-1448 kPa). The outlet of HPR is the intermediate pressure stage.
2. Intermediate Pressure Regulator Stage With pressure between 110-210 psi (758-1448 kPa), fuel exiting HPR flows through intermediate fuel line to LPL solenoid. LPL solenoid is controlled by AF ECM. Fuel flows out of LPL and into Intermediate Pressure Regulator (IPR). IPR reduces fuel pressure to 43-46 psi (246-317 kPa). Fuel flows out of IPR and into fuel rails.

The number below refers to step number in diagnostic procedure.

1. 2 This step verifies adequate fuel exists in CNG fuel tank.
2. 3 This step verifies Fuel Rail Pressure (FRP) sensor is displaying correct fuel pressure.
3. 4 This step tests for a leak in fuel system between Low Pressure Lock-Off (LPL) solenoid and fuel injectors. Fuel pressure should remain constant during test.
4. 5 This step tests High Pressure Regulator (HPR) output pressure. If fuel pressure is within specified values, HPR, fuel lines, and filters are okay.
5. 6 This step tests operation of High Pressure Lock-Off (HPL) solenoid. Cycle ignition quickly from Lock to Run position as you listen for HPL operation.
6. 8 This step tests for an electrical condition that is causing an inoperative HPL. If test light does not illuminate, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits.
7. 9 This step tests High Pressure Regulator (HPR) output pressure. If fuel pressure is within specified values, HPR, fuel lines, and filters are okay.
8. 12 This step tests for an electrical condition causing an inoperative LPL. If test light does not illuminate, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits.
9. 16 This step verifies fuel filter is not the cause of condition. If fuel pressure is within specified range after fuel filter replacement, a plugged filter was cause of condition.

The lock-off relay coil is supplied power whenever Powertrain Control Module (PCM) energizes gasoline fuel pump relay. When lock-off relay is energized, it supplies power to High Pressure Lock-Off (HPL) solenoid and Low Pressure Lock-Off (LPL) solenoid. At initial ignition ON, PCM energizes gasoline fuel pump relay Control circuit, which supplies power to fuel pump power circuit for a 2 second prime pulse. At initial ignition ON, Alternative Fuels Engine Control Module (AF ECM) will close HPL Control circuit, completing circuit path to ground, to allow for a 2 second CNG prime pulse. The prime pulse occurs at the same time as gasoline fuel pump prime pulse occurs. PCM will supply power to fuel pump relay Control circuit regardless of fuel system that is in operation as long as crankshaft pulses are received.

The numbers below refer to step numbers in diagnostic procedures.

1. 1 Diagnostic System Check must be performed before proceeding with this diagnostic procedure. Failure to perform system check will result in misdiagnosis.
2. 4 PCM energizes Fuel Pump Relay Control circuit for about 2 seconds every time ignition is cycled from OFF to ON.

The numbers below refer to step numbers in diagnostic procedures.

1. 1 System Check must be performed before proceeding with diagnostic procedure. Failure to perform System Check will result in misdiagnosis.

The numbers below refer to step numbers in diagnostic procedure.

1. 4 This step determines if an open IGN E fuse is causing condition.
2. 5 This step tests for a short to ground on ignition Voltage Supply circuit of fuel injector relay.
3. 6 This step determines if one of the fuel injector relays is causing condition. If IGN E fuse opens when a fuel injector relay is installed, replace relay.
4. 7 This step determines if AF fuel pump relay is causing condition. If IGN E fuse opens when AF fuel pump relay is installed, replace relay.
5. 8 This step determines if AF ECM is causing condition. If IGN E fuse opens when harness connector of AF ECM is installed, replace AF ECM.
6. 9 This step tests ignition voltage circuit of fuel injector relays.
7. 10 This step tests battery voltage circuit of fuel injector relays.
8. 11 This step tests battery voltage circuit of fuel injector relays for a short to ground. If test light illuminates, repair short to ground and replace fusible link.
9. 12 This step tests battery voltage circuit of fuel injectors for a short to ground between fuel injector relay and fuel injectors. If test light illuminates, repair short to ground and replace fusible link.
10. 14 This step tests fuel injector relays. If test light does not illuminate, inspect appropriate relay for proper terminal connections.

The numbers below refer to step numbers in diagnostic procedures.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within.5 ohms of each other. If highest resistance value is within.5 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
2. 5 If pressure drop value for each fuel injector is within 2 psi (14 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
2. 4 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG)»(ref-150429-S03967267952002111300000) .
3. 5 If pressure drop value for each fuel injector is within 2 psi (14 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step checks for a fuel heater that is stuck ON.
2. 3 This steps checks for a thermostatic switch that completes the circuit.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step checks for a fuel heater that is stuck ON.
2. 3 This steps checks for a thermostatic switch that completes the circuit.

The number below refers to step number in diagnostic procedure.

1. 7 This steps checks for a properly operating thermostatic switch that completes the circuit.

If an injection nozzle is not properly delivering fuel into pre-combustion chamber of cylinder, driveability could be greatly effected, or a Diagnostic Trouble Code (DTC) could be set. If other diagnosis indicates, or if injection nozzles are suspected of not properly delivering fuel, they should be tested. Typically, a nozzle failure can be detected by using injector balance test. Nozzle testing is comprised of the following checks

1. «INJECTOR BALANCE TEST»(ref-150429-S18007265852002112600000)
2. «NOZZLE OPENING PRESSURE TEST»(ref-150429-S30759442132002111300000)
3. «NOZZLE LEAK TEST»(ref-150429-S35532230732002111300000)

The numbers below refer to step numbers in diagnostic procedure.

1. 3 A balance rate between -4 mm 3 and 4 mm 3 will not cause a driveability concern. A balance rate less than -4 mm 3 , and between 4 mm 3 and 14 mm 3 will cause a driveability concern without any DTCs. A balance rate of more than 15 mm 3 will set a DTC.
2. 4 This step determines if ECM can control a stable fuel pressure. A high balance rate may be caused by a fuel injector or compression only if ECM can control fuel pressure.

The numbers below refer to numbers in diagnostic procedure.

1. 1 This step will make sure Diagnostic System Check-Engine Controls is performed.
2. 2 This step will make sure there are no other DTCs stored that will affect operation of glow plug system.
3. 3 This step will check each glow plug for an open.
4. 4 This step will check each glow plug feed circuit for an open.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step will make sure there are no other DTCs stored that will affect operation of glow plug system.
2. 3 This step will check each glow plug for an open.
3. 4 This step will check each Glow Plug Feed circuit for an open.

The numbers below refer to step numbers in diagnostic procedure.

1. 4 This step tests Ignition 1 Relay Control circuit from ECM.
2. 5 This step isolates circuit from IGN relay. All circuits at relay are good if test light illuminates.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 A water-in-fuel light that is ON is normal if there is water-in-fuel.
2. 5 This step determines if there is a short to ground in Light Control circuit between sensor and water-in-fuel indicator bulb.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step determines if Ignition Feed circuit is open.
2. 4 This step determines if Ground circuit is okay.
3. 5 This step determines if fuse, bulb, and wiring are okay.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 1)

Scheme 1

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 1)

Scheme 2

The number below refers to step number in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.

Scheme 3

The number below refers to step number in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 4)

Scheme 4

The number below refers to step number in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. see scheme 8

The number below refers to step number in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. see scheme 9

The number below refers to step number in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. see scheme 10

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «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.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «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.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 1)

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «FUEL SYSTEM PRESSURE TEST (3.4L)»(ref-149936-S29348623012002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «FUEL SYSTEM PRESSURE TEST (3.4L)»(ref-149936-S29348623012002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 2)

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «FUEL SYSTEM PRESSURE TEST (4.2L)»(ref-149936-S28337785802002112600000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «FUEL SYSTEM PRESSURE TEST (4.2L)»(ref-149936-S28337785802002112600000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 3)

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «FUEL SYSTEM PRESSURE TEST (4.3L)»(ref-149936-S33836779402002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «FUEL SYSTEM PRESSURE TEST (4.3L)»(ref-149936-S33836779402002111400000) under BASIC FUEL SYSTEM CHECKS (GASOLINE) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. (Scheme 4)

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «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.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «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.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. see scheme 8

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «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.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «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.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. see scheme 9

The numbers below refer to step numbers in diagnostic procedure.

1. 3 Engine Coolant Temperature (ECT) must be below operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 Fuel pressure should be within specified range. If fuel pressure is not within specified range, see «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.
3. 5 Fuel pressure should reach a steady value. If fuel pressure does not stabilize, see «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.
4. 6 If pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of average pressure drop value, fuel injectors are flowing properly. Calculate pressure drop value for each fuel injector by subtracting second pressure reading from first pressure reading. see scheme 10

The numbers below refer to step numbers in diagnostic procedure.

1. 4 This step tests for a short to ground on Ignition 1 Voltage Supply circuit of fuel injector.
2. 5 This step tests for a short to a PCM ground on Ignition 1 Voltage Supply circuit of fuel injector.
3. 6 This step tests for a short to ground between multi-way connector and fuel injectors.
4. 7 This step tests for an open or high resistance between multi-way connector and fuel injectors.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests for an open Ignition 1 Voltage Supply circuit between PCM 1 fuse and multi-way connector.
2. 4 This step tests for an open or high resistance between multi-way connector and fuel injectors.

The numbers below refer to step numbers in diagnostic procedure.

1. 4 This step tests for a short to ground on Ignition 1 Voltage Supply circuit of fuel injector.
2. 5 This step tests for a short to a PCM ground on Ignition 1 Voltage Supply circuit of fuel injector.
3. 6 This step tests for an open Ignition 1 Voltage Supply circuit between ECM 1 fuse and multi-way connector.
4. 7 This step tests for high resistance between ECM 1 fuse and multi-way connector.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.
2. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
3. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
4. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any fuel injectors display a resistance outside of specified value, replace fuel injector.
2. 4 This step determines if all fuel injectors are within 3 ohms of each other. If highest resistance value is within 3 ohms of lowest resistance value, then all fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting highest and lowest resistance values from average value, replace fuel injector that has greatest resistance difference from average.

The number below refers to the step number in the diagnostic procedures.

1. 2 Using scan tool, command both ON and OFF states. Repeat commands as necessary.
2. 3 This step determines if condition is located on coil side or switch side of circuit.
3. 4 This step verifies that PCM is providing voltage to fuel pump relay.
4. 5 This step tests for an open in ground circuit to fuel pump relay.
5. 6 This step determines if voltage is constantly being applied to fuel pump relay.
6. 13 This step determines if condition with circuit is intermittent. If fuse does not open, inspect supply voltage circuit between fuse and fuel pump for an intermittent condition.
7. 15 Use the same amperage fuse in jumper as is used to protect fuel pump circuit.
8. 17 Inspect splice pack which contains fuel pump ground and other ground circuits. Be certain all connections within splice pack are clean and tight.

The number below refers to the step number in the diagnostic procedures.

1. 2 Command both ON and OFF states. Repeat commands as necessary.
2. 3 This step determines if condition is located on coil side or switch side of circuit.
3. 4 This step verifies PCM is providing voltage to fuel pump relay.
4. 5 This step tests for an open in fuel pump relay ground circuit.
5. 6 This step determines if voltage is constantly being applied to fuel pump relay.
6. 12 This tests for a grounded fuel pump supply voltage circuit. The fuel pump fuse supplies power to fuel pump. Disconnecting fuel pump in-line harness connector isolates fuel pump supply voltage circuit.
7. 15 This step jumps fuel pump relay in order to activate fuel pump.
8. 16 This step tests for an open in fuel pump feed circuit between in-line connector and fuel pump relay.
9. 17 This step tests for an open or high resistance in fuel pump ground circuit.
10. 20 This step determines if condition with circuit is intermittent. If fuse does not open, inspect supply voltage circuit between fuse and fuel pump for an intermittent condition.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step determines if condition is current.
2. 4 This step verifies PCM is providing voltage to fuel pump relay.
3. 5 This step tests for an open in ground circuit to fuel pump relay.
4. 6 This step determines if voltage is constantly being applied to fuel pump relay.
5. 13 This step determines if condition with circuit is intermittent.
6. 15 This step determines if fuel pump will operate while bypassing fuel pump relay.

Engine idle speed is controlled by Idle Air Control (IAC) valve. IAC valve is on throttle body. IAC valve pintle moves in and out of an idle air passage bore to control air flow around throttle plate. IAC valve consists of a movable pintle, driven by a gear attached to a 2 phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is fed by 2 circuits from Powertrain Control Module (PCM). When PCM changes polarity of a coil, stepper motor moves one step. PCM uses a predetermined number of counts to determine IAC pintle position. Observe IAC counts with scan tool. IAC counts will increment up or down as PCM attempts to change IAC valve pintle position. An IAC Reset will occur when ignition key is turned OFF. First, PCM will seat IAC pintle in idle air passage bore. Second, PCM will retract pintle a predetermined number of counts to allow for efficient engine start-up. If engine idle speed is out of range for a calibrated period of time, an idle speed Diagnostic Trouble Code (DTC) may set.

The numbers below refer to step numbers in diagnostic procedure.

1. 5 This test will determine ability of PCM and IAC valve circuits to control IAC valve.
2. 7 This test will determine ability of PCM to provide IAC valve circuits with ground. On a normally operating system, test light should not flash while IAC counts are incrementing.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between IC module and Powertrain Control Module (PCM) consist of the following

1. Low reference circuit.
2. Low resolution engine speed signal.
3. Two IC timing control signals for cylinders No. 1 and 4, and for cylinders No. 2 and 3.

IC module and PCM use low resolution engine speed signal to control ignition operation. Low resolution engine speed signal is derived from Crankshaft Position (CKP) sensor, which is connected directly to IC module.

The numbers below refer to step numbers in diagnostic procedure.

1. 4 Repair cause of malfunctioning spark plugs before replacing.
2. 5 Inspect for basic engine malfunction like low compression, burnt valves, worn timing chain and worn gears, etc.
3. 18 Any time CKP sensor is removed crankshaft position variation learn procedure must be performed.
4. 22 Replacement PCM must be reprogrammed and CKP system variation learn procedure must be performed.

Ignition Control (IC) module has independent power and ground circuits. Circuits between IC module and Powertrain Control Module (PCM) consist of the following circuits

1. IC timing signal.
2. IC timing control.
3. Low-resolution engine speed signal.
4. Low reference signal.

IC module sends 3x signals to PCM. IC module controls timing advance during engine cranking. Timing advance changes to PCM control after the following actions

1. PCM receives the second 3x signal.
2. PCM applies 5 volts to IC timing signal circuit.
3. Timing advance switches to PCM control.

The numbers below refer to step numbers in diagnostic procedures.

1. 3 It is necessary to disconnect 24x crank sensor in order to ensure that 7x signal is read in 3x reference parameter.
2. 4 Spark Tester (J 26792) presents a more difficult load on secondary ignition than a normal spark plug. If a miss or a hesitation is caused by a spark plug that is not firing, spark tester should also not fire.
3. 5 Use a 5 percent saltwater solution in a spray container to induce voltage arcing to ground through faulty insulation of spark plug wires.
4. 7 If no spark condition follows suspected coil, that coil is faulty. Otherwise, ignition module is cause of no spark. This test can also be performed by substituting a known good coil for one causing no spark condition.

Electronic ignition system uses an individual ignition coil for each cylinder. Powertrain Control Module (PCM) controls ignition operation through 6 Ignition Control (IC) circuits. Each ignition coil is connected to PCM, power, or ground by the following circuits

1. Ground.
2. Ignition 1 voltage.
3. Appropriate IC Control circuit.

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

The number below refers to step number in diagnostic procedure.

1. 5 A few sparks, then nothing, is considered no spark.

This system includes distributor, Camshaft Position (CMP) sensor, ignition coil with Ignition Control Module (ICM), secondary wires, spark plugs, Knock Sensors (KS) and Crankshaft Position (CKP) sensor. The ignition system is controlled by Powertrain Control Module (PCM). PCM monitors information from various engine sensors, computes desired spark timing, and controls dwell and firing of ignition coil via an IC line to IC module.

Note. Battery should be fully charged prior to any tests.

The numbers below refer to step numbers in diagnostic procedure.

1. 3 This step checks for proper spark output. Spark test requires a minimum of 25,000 volts to operate. This check can be used in case of an ignition miss, because system may provide enough voltage to run engine but not enough to operate a spark plug under heavy load.
2. 4 This test separates distributor cap, rotor, and ignition wires from ignition coil in order to help identify a secondary ignition system problem.
3. 6 This test checks Ignition Control Module (ICM), connections and wiring.
4. 12 This test begins to determine if PCM is providing a signal to ICM. If PCM is not providing a signal to ICM, problem exists between ICM and PCM.
5. 14 This test checks for a basic engine mechanical problem.

The numbers below refer to step numbers in diagnostic procedure.

1. 4 Monitoring misfire current counters determines if a fault is present.
2. 11 A good indication that fuse is open, is all misfire current counters are incrementing on one side of engine. Inspect ignition positive voltage circuit for a grounded circuit. If fuse is open and ignition coil circuits are okay, inspect injector circuits for being grounded.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step is testing battery positive voltage circuit of ignition relay.
2. 3 This step is testing Ignition 1 positive voltage circuit of ignition relay.
3. 4 This step is testing coil ground circuit of ignition relay.
4. 5 This step isolates circuits from ignition relay. All circuits at relay are good if test light illuminates.

The numbers below refer to step numbers in diagnostic procedure.

1. 4 This step is testing relay ground circuit.
2. 5 This step isolates circuit from IGN relay. All circuits at relay are good if test light illuminates.
3. 9 The open circuit will be between splice and IGN relay.
4. 10 Remove underhood electrical center cover and inspect circuits that are supplied a voltage by IGN relay.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step is testing battery positive voltage circuit of ignition relay.
2. 3 This step is testing Ignition 1 positive voltage circuit of ignition relay.
3. 4 This step is testing coil ground circuit of ignition relay.
4. 5 This step isolates circuits from ignition relay. All circuits at relay are good if test light illuminates.

The numbers below refer to step numbers in diagnostic procedure.

1. 1 The System Check must be performed before proceeding with this diagnostic test. Failure to perform System Check will result in misdiagnosis.
2. 3 This step inspects Alternative Fuels Engine Control Module (AF ECM) fuses for opens and also tests voltage supply to fuses.
3. 5 This step inspects if AF ECM is powered-up.
4. 6 This step tests battery positive and switched ignition voltage circuits to AF ECM.
5. 7 This step tests AF ECM ground circuits.
6. 8 This step inspects for proper operation of fuel gauge select switch. If switch operates, then ignition relay is ON.
7. 11 This step inspects ignition relays ability to turn OFF.
8. 14 This step tests ignition relay coils ground circuit. If test light illuminates, then ignition relay must be faulty.
9. 15 This step indicates components or circuits that may have caused a fuse to open. Some components may require they be turned on in order to open fuse. An example would be depressing fuel gauge select switch in order to test select switch circuit for a short.

The numbers below refer to step numbers in diagnostic procedure.

1. 2 This step is testing battery positive voltage circuit of ignition relay.
2. 3 This step is testing Ignition 1 positive voltage circuit of ignition relay.
3. 4 This step is testing coil ground circuit of ignition relay.
4. 5 This step isolates circuits from ignition relay. All circuits at relay are good if test light illuminates.

Fuel Tank Leak Test is used to locate any fuel or fuel vapor escaping fuel tank area. Fuel vapors escaping above fuel level will be detected when Evaporative (EVAP) emission diagnostics complete one test cycle. Malfunction Indicator Lamp (MIL) will illuminate after EVAP diagnostics complete 2 test cycles.

The numbers below refer to step numbers in diagnostic procedures.

1. 1 Perform this procedure in order to determine that no EVAP diagnostic DTC is present.
2. 3 This test is to locate fuel leakage in fuel lines.
3. 4 This tests for fuel leaks below fuel tank fuel level.
4. 5 This test is to locate fuel vapors escaping above fuel level in fuel tank.