Engine Controls - System & Component Testing - 6.5l (G Series) Chevrolet Chevy Van G3500

INTRODUCTION

Before testing separate components or systems, perform procedures in the BASIC TESTING - 6.5L DIESEL article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in the TESTS W/CODES - 6.5L article.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter and refer to the WIRING DIAGRAMS article to isolate wiring harness shorts or opens.

The following table provides the location of commonly used diagnostic information.

GENERAL MOTORS REFERENCE

TURBOCHARGER

Note. For symptom diagnosis see TESTS W/O CODES - 6.5L article or the TESTS W/CODES - 6.5L article.

A problem in turbocharger boost system will set a related diagnostic trouble code. See the TESTS W/CODES - 6.5L article.

COMPUTERIZED ENGINE CONTROLS

Note. 6.5L diesel engines are equipped with a Powertrain Control Module (PCM).

CONTROL UNIT

Note. To perform the following ground and power tests, use appropriate wiring diagram in the WIRING DIAGRAMS article.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on PCM ground terminals. Resistance should be zero ohms. If not, repair open to ground.
2. Using a voltmeter, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is more than one volt, check for open, corrosion or loose connection on ground circuit.

Power Circuits

1. Using a voltmeter, check for battery voltage between PCM continuous power terminal(s) and ground. If battery voltage is not present, check for blown fuse or open fusible link. If okay, check for open in wire between PCM terminal and power source.
2. Turn ignition on. Using a voltmeter, check for battery voltage between PCM ignition power terminals and ground. If battery voltage is not present, check IGN fuse. If fuse is okay, check for an open in wire between battery and ignition switch, and between ignition switch and PCM terminal. If okay, check for a defective ignition switch.
3. Connect voltmeter between ground and PCM starter (crank) signal terminal. On vehicles with manual transmission/transaxle, depress clutch pedal. Turn ignition switch to START position. Battery voltage should be present ONLY when ignition switch is in START position.
4. If voltage is not present, check CRANK fuse or fusible link between ignition switch and PCM terminal. If fuse or fusible link is okay, check for an open in wire between ignition switch and PCM terminal, or check for a defective ignition switch.

A/C ON SWITCH/SYSTEM TEST

1. Turn ignition switch to RUN position. Move mode selector switch to any position other than OFF position. With A/C control assembly connected, measure voltage between mode selector switch Light Green wire and ground. For wiring schematics, see the WIRING DIAGRAMS article.
2. Battery voltage should be present. If battery voltage is present, mode selector switch is operating normally. If battery voltage is not present, check wire from mode selector switch to fuse for an open circuit. Also check A/C high and low pressure switches for open.
3. Check voltage between mode selector switch Dark Green/White wire or Light Green wire and ground. Voltage should not be present. If voltage is present, replace mode selector switch.

BRAKE SWITCH

Disconnect brake switch harness connector. Using an ohmmeter, check continuity between brake switch terminals. Continuity should be present. Depress brake pedal or activate brake switch, continuity should not be present.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

If a coolant sensor-related code is present, see the TESTS W/CODES - 6.5L article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test sensor calibration. Disconnect ECT sensor connector. Measure resistance between sensor terminals. Resistance should be high when engine is cold and drop as engine warms. See ECT SENSOR RESISTANCE VALUES table.

ECT SENSOR RESISTANCE VALUES

Note. Intake Air Temperature (IAT) sensor is also referred to as Manifold Air Temperature (MAT) sensor.

INTAKE AIR TEMPERATURE (IAT) SENSOR

If an IAT sensor-related code is present, see the TESTS W/CODES - 6.5L article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test calibration. Disconnect IAT sensor harness connector. Connect ohmmeter between sensor terminals. Sensor resistance should be as specified. See IAT SENSOR RESISTANCE table. With vehicle sitting overnight, IAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE

KNOCK SENSOR

1. Disconnect knock sensor harness connector. Using an ohmmeter, measure knock sensor resistance between sensor terminal and engine block. Resistance should be 3300-4500 ohms. Connect voltmeter between sensor terminal and ground. Set voltmeter to 2-volt AC scale.
2. Start and idle engine. Tap on engine block near sensor. A signal should be indicated on voltmeter. If no signal is indicated, replace knock sensor. Also see «TIMING CONTROL SYSTEMS»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series) under IGNITION SYSTEM and the «TESTS W/CODES - 6.5L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel-g-series) article.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

1. MAP sensor circuit malfunction should set a related code in PCM memory. If a code is present, see the «TESTS W/CODES - 6.5L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel-g-series) article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test sensor calibration. If driveability problems exist, MAP sensor failure is suspected and no MAP code is present, disconnect MAP sensor connector. If driveability condition improves, check MAP vacuum hose for splits, kinks, proper routing and blockage. If no problems are found, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tool connected to Data Link Connector (DLC). Voltage should be as specified in «MAP SENSOR VOLTAGE RANGE»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series) table.
3. If MAP sensor voltage is as specified, go to next step. If voltage is not as specified, check 5-volt reference supply to sensor. Check harness integrity. If no problems are evident, replace MAP sensor.
4. Using a hand-held vacuum pump, apply 10 in. Hg to MAP sensor and note voltage change. Voltage should drop to about 1.0-2.5 volts less than specified in table. If voltage is not as specified or voltage reading does not immediately follow vacuum change, MAP sensor is faulty.

MAP SENSOR VOLTAGE RANGE

OXYGEN SENSOR (O2S)

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect DVOM between Purple wire of oxygen sensor and ground. Place DVOM on 2-volt scale.
2. Using another DVOM on 20-volt scale, connect DVOM in series between Purple wire from PCM and positive post of battery. This will simulate a rich condition, causing PCM to respond by leaning mixture. Reading on DVOM connected to oxygen sensor should decrease to less than .3 volt.
3. Move DVOM lead from positive battery post to negative battery post. This will simulate a lean condition, causing PCM to respond by richening mixture. Reading on DVOM connected to oxygen sensor should increase to greater than .8 volt. If reading does not change as specified, replace oxygen sensor.
4. If a second DVOM is not available, connect a jumper in Purple wire from PCM. Hold jumper in one hand and touch positive post of battery with other hand to simulate a rich condition. Touch negative post of battery to simulate a lean condition. For additional testing procedures, see the «TESTS W/CODES - 6.5L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel-g-series) article.

OXYGEN SENSOR HEATING ELEMENT

On models with oxygen sensor heating elements, disconnect 3-wire connector at oxygen sensor. Measure resistance between White wire terminals on sensor side of connector. Resistance should be 3.5-14 ohms at 68°F (20°C). If resistance is not 3.5-14 ohms, replace oxygen sensor.

THROTTLE POSITION (TP) SENSOR

1. Install jumper wires to enable connection of a DVOM in parallel between TP sensor harness connectors. Connect DVOM positive lead to Dark Blue wire terminal. Connect negative lead to Black wire terminal. (Scheme 47)
2. Turn ignition on, engine off. Slowly depress accelerator pedal. Signal voltage should gradually change from less than one volt at closed throttle to about 5.0 volts at wide open throttle position. If reading is not as specified, replace TP sensor.
3. TP sensor circuit malfunction should set a related trouble code. For further information, see the «TESTS W/CODES - 6.5L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel-g-series) article. Also see TP SENSOR ADJUSTMENT in the «ADJUSTMENTS - 6.5L DIESEL»(/chevrolet/chevy-van-g3500/1996-1998/remont/adjustments/#engine-performance-system-adjustments-65l-diesel-g-series) article.

Scheme 47

TRANSMISSION RANGE SWITCH

A problem in transmission range switch circuit will set related diagnostic trouble code. See the TESTS W/CODES - 6.5L article.

VEHICLE SPEED SENSOR (PM GENERATOR)

Disconnect vehicle speed sensor harness connector (located in transmission/transaxle). Place gear selector in Neutral. Raise vehicle drive wheels off the ground. Turn drive wheels by hand (more than 3 MPH). Measure AC signal voltage between sensor terminals. Voltage reading should vary from 0.1 to 0.5 volt AC as wheel is turned. If reading is not as specified, replace vehicle speed sensor. If a code is set, refer to the TESTS W/CODES - 6.5L article.

RELAYS

Note. To perform the following tests, use the WIRING DIAGRAMS article.

A/C Clutch Relay

See MISCELLANEOUS PCM CONTROLS .

Fuel Pump Relay

1. If a prolonged crank is required to start vehicle, fuel pump relay may be faulty. To verify, start engine. With engine running, disconnect oil pressure switch (fuel pump back-up circuit). If engine stalls, fuel pump relay is faulty. If vehicle continues to run, relay is okay. Check for other causes of prolonged crank.
2. To test fuel pump relay, disconnect fuel pump relay. Refer to «COMPONENT LOCATIONS»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series__component-locations) . Apply battery voltage and ground to fuel pump relay winding terminals (control and ground).
3. Using an ohmmeter, check continuity between fuel pump relay control and ground terminals. Continuity should exist. If continuity does not exist, fuel pump relay is defective.
4. To by-pass fuel pump relay on vehicle (fuel pump not operating), turn ignition off. Disconnect fuel pump relay connector. Using a fused jumper wire, connect fuel pump test connector to positive side of battery. Fuel pump should run.
5. If fuel pump runs, check for faulty connections to relay or replace defective relay. To locate fuel pump test connector, refer to «COMPONENT LOCATIONS»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series__component-locations) .

SOLENOIDS

Note. All PCM-controlled solenoids should have at least 20 ohms of resistance (except fuel injectors).

Canister Purge Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Torque Converter Clutch (TCC) Solenoid

See MISCELLANEOUS PCM CONTROLS .

FUEL SYSTEM

Note. For complete system testing and diagnosis, see the TESTS W/CODES - 6.5L article.

A normal functioning system should operate as follows

1. With ignition switch in ON position, engine not running and at room temperature, glow plugs are on for 4-6 seconds, then off for about 4.5 seconds. Following this on-and-off cycle, glow plugs are on for about one second and off for about 3 seconds. The glow plugs continue to cycle on and off in this time sequence for about 16 seconds.
2. If engine is cranked during or after the above sequence, glow plugs will cycle on and off for a total duration of 25 seconds after ignition switch is returned from crank position, whether engine starts or not. Engine does not have to be running to terminate glow plug cycling.

Note. Glow plug on-and-off times vary with engine temperature, system voltage and/or ambient temperature. Lower temperatures cause longer duration of cycling.

PRELIMINARY GLOW PLUG DIAGNOSIS

1. If system does not operate as described in «NORMAL GLOW PLUG CIRCUIT OPERATION»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series) , ensure glow plug system is correctly installed. Ensure all connectors are properly attached, clean and tight. Inspect engine harness ground connection. Ensure nuts securing glow plug relay to engine are tightened to 31 ft. lbs. (42 N.m). Ensure connector is fully seated in relay.
2. Ensure glow plug relay copper stud upper nuts are tightened to 44 INCH lbs. (5 N.m). DO NOT overtighten nuts. Inspect WAIT TO START light on instrument panel for tight connection and proper operation.

Electrical Check

Turn ignition off. Disconnect all glow plug connectors. Using an ohmmeter, check resistance between each glow plug terminal and ground. Glow plug resistance should be more than 2 ohms. Replace glow plug if resistance is not as specified.

NO START (COLD)

Perform these diagnostic procedures if engine does not start when cold; GLOW PLUG light (WAIT TO START light) may or may not come on. Before proceeding, check fuel system to ensure it is okay. Ensure battery voltage is 12.4 volts or more with ignition turned off. Ensure cranking speed is at least 100 RPM.

1. Turn ignition off. Check voltage at battery stud (single lead) on glow plug. (Scheme 48) If voltage is present, go to next step. If voltage is not present, repair battery-to-glow plug relay circuit.
2. If voltage was present in step 1), turn ignition off and check voltage at glow plug feed stud (twin lead) on glow plug relay. If battery voltage is present, go to next step. If battery voltage is not present, relay contacts are shorted. Replace relay and all glow plugs.
3. If voltage is present in step 2), disconnect harness from all glow plugs. Check resistance between glow plug terminals and engine block. Replace glow plug if resistance is more than 2 ohms. Reconnect all glow plugs before continuing with diagnosis.
4. With all glow plugs reconnected, place ignition switch in RUN position. Remove relay connector and check voltage at harness connector terminal "D". (Scheme 48)
5. If no voltage is present, repair open in ignition feed circuit to relay. If voltage is present, check resistance between terminal "E" of connector and engine block (ground). If resistance is more than one ohm, repair ground circuit to relay.
6. With ground circuit working properly in step 4), check resistance between terminals "C" and "E" of connector. If reading is more than 2 ohms, go to next step. If reading is less than 2 ohms, go to step 8).
7. If reading in step 6) was more than 2 ohms, check for excessive resistance in voltage sense circuit to relay. Repair as necessary.
8. If reading in step 6) was less than 2 ohms, reconnect relay harness connector and ensure complete engagement. Connector locking latch should click over relay locking tab. With relay connector harness correctly connected, check voltage at glow plug feed stud (twin lead) on glow plug relay, while turning ignition switch from OFF position to RUN position.
9. If voltage is not present, replace glow plug relay. If battery voltage is present, check voltage at any one glow plug harness connector when turning ignition switch from OFF to RUN position. Test both right and left banks.
10. If no voltage was present in step 9), repair glow plug feed circuit to glow plugs. If battery voltage is present and instrument panel GLOW PLUG light (WAIT TO START light) does not come on, locate and repair bulb or circuit.

Scheme 48

GLOW PLUG RELAY

Note. To perform following test, use WIRING DIAGRAMS article.

1. Ensure coolant temperature is less than 80°F (27°C) before beginning test. Place ignition switch in RUN position and allow glow plugs to cycle. After 2 minutes, crank engine for one second. It is NOT important that engine starts. Return ignition switch to RUN position. Glow plugs should cycle on at least once.
2. If glow plugs do not cycle, disconnect relay (relay is located on top rear of engine). Connect test light between Pink wire terminal of harness connector (terminal "A") and ground. With ignition switch in RUN position, test light should be off. Test light should illuminate when engine is cranked.
3. If test light does not illuminate as specified, repair short or open in engine harness Pink wire. If test light illuminates as specified but glow plugs do not cycle, replace relay.

INJECTION PUMP HOUSING LEAKAGE TEST

1. Remove injection pump and drain all fuel. Connect an air supply line to fuel inlet fitting. Ensure air supply is clean and dry. Seal off return line fitting. Completely immerse pump assembly in a container of clean test oil.
2. Apply 20 psi (1.4 kg/cm 2 ) to pump. Leave pump immersed for 10 minutes to allow trapped air to escape. Watch for leaks after 10 minutes. If no leaks are observed after 10 minutes, reduce air pressure to 2 psi (.14 kg/cm 2 ) for 30 seconds.
3. If there are still no leaks, increase pressure to 20 psi (1.4 kg/cm 2 ) again. If no leaks are observed, pump is ready for use. If leaks are noticed, replace pump.

Test Preparation

1. Remove injector nozzles from engine. Clean carbon from tip area of nozzle with soft brass wire brush. DO NOT use steel brush or motorized brush to clean nozzle tip. Damage to nozzle tip may result. CAUTION: Use Nozzle Socket (J-29873) to remove and replace injection nozzle. Attach socket to 30-mm hex portion of nozzle. Failure to do so will result in damage to injector nozzle.
2. Connect injector nozzle to injection nozzle tester. Place clear plastic tubing on both fuel return fittings to prevent bleed-off from being confused with leaks. Close tester shutoff valve to pressure gauge.
3. Fill tester with test fluid. Fill and flush nozzle assembly with test fluid by operating tester lever briskly and repeatedly. This purges air from injector nozzle and coats all parts with test fluid.

Opening Pressure Test

1. Open tester shutoff valve 1/4 turn from closed position. Slowly depress tester lever and observe gauge. Note pressure at which needle of pressure gauge stops. Some injector nozzles may pop while other injector nozzles may drip (this is not a leak).
2. Injector opening pressure should not fall to less than 1500 psi (105 kg/cm 2 ). Replace any injector nozzle that does not meet lowest acceptable pressure. Release tester pressure.

Leakage Test

1. Open tester shutoff valve 3/4 to 1 3/4 turns from closed position. Blow dry injector nozzle tip. Slowly depress tester lever until pressure gauge reads 1400 psi (98 kg/cm 2 ). Maintain pressure for 10 seconds and observe injector nozzle tip.
2. A drop may form on end of injector nozzle, but should not fall off within a 10 second period. Replace injector nozzle if a drop of test fluid falls from tip during 10 second period. (Scheme 49) Release tester pressure.

Scheme 49

Chatter Test

Chatter for new and used injector nozzles may vary. With some used injector nozzles, chatter is difficult to detect during slow actuation of tester lever. Some injector nozzles may chatter louder than others. As long as there is chatter, injector nozzle is acceptable.

1. Close tester shutoff lever at pressure gauge. Slowly depress lever and note whether chatter is heard. If no chatter is heard, increase speed of lever movement until it reaches a point at which injector nozzle chatters.
2. At fast lever movement, injector nozzle may emit a "hissing" or "squealing" sound rather than normal chatter. This is acceptable. These sounds indicate that injector nozzle needle moves freely and injector nozzle seat, guide and pintle have no mechanical defects. Replace any injector nozzle assembly that does not chatter.

Spray Pattern Test

The injector nozzles used with this system have several features that make pattern testing difficult. These features include longer nozzle overlap, greater pintle-to-body clearances and an internal wave washer between injector nozzle nut and injector. Typical injector nozzle tester cannot deliver fuel with sufficient velocity to obtain proper spray patterns. DO NOT replace injector nozzle(s) based on spray pattern.

IGNITION SYSTEM

Note. For basic ignition system checks, see the BASIC TESTING - 6.5L DIESEL article.

Knock Sensor Circuit (Models Using External Spark Controller Module)

1. An open or short circuit on IC module control wire to PCM will cause a loss of 12-volt IC module signal. This will cause PCM to fully retard ignition timing.
2. If a scan tool is available, connect tester to Data Link Connector (DLC). Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, backprobe PCM knock sensor signal terminal with a DVOM. With engine idling, 8-12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at PCM terminal should drop to zero volts, and return to original voltage when knock signal ceases.
4. If voltage signal does not respond as described, check knock sensor-to-module-signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. See KNOCK SENSOR under «ENGINE SENSORS & SWITCHES»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series) .

Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)

1. An open or short circuit on knock sensor wire to PCM will set a related trouble code. A false detonation signal will not cause PCM to set a code.
2. If a scan tool is available, connect it to Data Link Connector (DLC). Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no RPM decrease occurred, check knock sensor to PCM circuit.
4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. See KNOCK SENSOR under «ENGINE SENSORS & SWITCHES»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-system-component-testing-65l-g-series) .

Crankcase Depression Regulator (CDR)

To test CDR valve, connect one hose of a water manometer to engine oil dipstick tube. Leave other hose of manometer open to atmosphere. Install air cleaner and run engine. CDR valve specification is one inch of water pressure at idle to 3-4 inches at full load. Add amount of distance water travels down one side of gauge to distance water travels up other side of gauge to obtain reading.

EGR Valve Check

With engine off, disconnect vacuum hose to EGR valve. Connect vacuum pump to EGR and apply 10 in. Hg. EGR diaphragm should move up and stay up for at least 20 seconds. If not, replace EGR valve.

VACUUM PUMP

Connect vacuum gauge to vacuum pump inlet (small fitting). DO NOT plug or disconnect outlet fitting. With engine idling, vacuum should be 18 in. Hg one minute after start. If not, check for belt slippage, vacuum leaks or other obvious defects. If no defects are present, replace vacuum pump.

MISCELLANEOUS PCM CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

TRANSMISSION

Note. To perform the following tests, use appropriate wiring diagram in the WIRING DIAGRAMS article.

Disconnect harness connector to TCC solenoid. Measure resistance between TCC solenoid terminals. Solenoid resistance should be 10-15 ohms at 68°F (20°C).

Note. Some solenoids have an internal pressure switch in series with solenoid winding and will not show continuity until transmission hydraulic pressure is applied.

Converter Lock-Up Signal At Transmission

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Disconnect converter clutch connector at transmission. Connect a test light across converter clutch harness terminals. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light is not on, check solenoid power supply wire of harness for open or short to ground. Check ground circuit for open between harness connector and PCM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM PCM.

Converter Lock-Up Signal From PCM

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Connect a test light to battery voltage. Touch TCC control driver terminal with test light. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty PCM connector or PCM.

Warning Light Diagnosis

1. Perform On-Board Diagnostics (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING - 6.5L DIESEL»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-65l-diesel-g-series) article. After performing OBD system check, go to next step.
2. Check instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. If instrument panel is okay, go to next step.
3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between affected PCM output circuit at PCM harness connector terminal and ground. See the WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
4. Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is as specified, go to step 12). If reading is not as specified, go to next step.
5. Disconnect instrument cluster, leaving PCM connector disconnected. Using DVOM, check voltage between affected PCM output circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, go to next step.
6. Locate and repair short to voltage in affected PCM output circuit. After repairs, go to step 17).
7. Check ignition feed fuse for instrument cluster indicator lights. If fuse is blown, go to next step. If fuse is okay, go to step 9).
8. Locate and repair short to ground in ignition feed circuit for instrument cluster indicator lights. Replace fuse and go to step 17).
9. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ignition feed circuit for instrument cluster indicator lights and ground. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 14).
10. Check affected PCM output circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, go to next step.
11. Check affected PCM output circuit and ignition feed circuit for poor connection at instrument cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not found, go to step 15).
12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between affected PCM output circuit and ignition feed circuit at instrument panel harness connector. Using a scan tool, perform OUTPUTS TEST function to cycle affected warning light on and off. If test light flashes on and off, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does not flash on and off, go to next step.
13. Check affected PCM output circuit for poor connection to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
14. Repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 17).
15. Replace instrument cluster and then go to step 17).
16. Replace PCM and then go to next step.
17. Using scan tool, operate affected warning light. If warning light does not operate properly, go to step 3).

Tachometer Control Circuit Diagnosis

1. Diagnose instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. After diagnosis, go to next step.
2. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING - 6.5L DIESEL»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-65l-diesel-g-series) article. After performing OBD system check, go to next step.
3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between tachometer control circuit at PCM harness connector terminal and ground. See the WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
4. Set DVOM to 10-amp scale. Check current between tachometer control circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is not as specified, go to next step. If reading is as specified, go to step 12).
5. Disconnect instrument cluster, leaving PCM connector disconnected. Using DVOM, check voltage between tachometer control circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, go to next step.
6. Locate and repair short to voltage in tachometer control circuit. After repairs, go to step 17).
7. Check ignition feed fuse for instrument cluster. If fuse is blown, go to next step. If fuse is okay, go to step 9).
8. Locate and repair short to ground in ignition feed circuit to instrument cluster. Replace fuse and go to step 17).
9. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ignition feed circuit for instrument cluster and ground. Battery voltage should be present. If battery voltage was not present, go to step 14). If battery voltage is present, go to next step.
10. Check tachometer control circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, go to next step.
11. Check tachometer control circuit and ignition feed circuit for poor connection at instrument cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not found, go to step 15).
12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between tachometer control circuit and ignition feed circuit at instrument panel harness connector. Using a scan tool, perform OUTPUTS TEST function to cycle tachometer control output light on and off. If test light flashes on and off, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does flash on and off, go to next step.
13. Check tachometer control circuit for poor connection to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
14. Repair open in ignition feed circuit to instrument cluster. After repairs, go to step 17).
15. Replace instrument cluster and then go to step 17).
16. Replace PCM and then go to next step.
17. Start engine and observe tachometer. If tachometer does not operate properly, diagnose instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section.

A/C COMPRESSOR CLUTCH CONTROLS

The A/C compressor clutch relay is controlled by the PCM. The PCM improves idle quality by delaying A/C compressor clutch engagement until idle speed is increased, or disengages A/C compressor clutch when idle speed is too low. A/C compressor clutch is cycled by PCM. PCM smooths cycling of A/C compressor clutch by adding fuel the instant A/C compressor clutch is applied.

Note. See the WIRING DIAGRAMS article for component location, terminal and wire color identification.

RELAY LOCATION

A/C COMPRESSOR CLUTCH RELAY LOCATION

Note. To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses. Ensure all related relay and wire harness connections are clean and tight. Repair as necessary.

Description

A/C clutch relay is controlled by Vehicle Control Module (VCM) to delay A/C clutch engagement after A/C is turned on. This allows VCM to adjust engine RPM before A/C clutch engages. VCM will engage A/C clutch any time A/C has been requested unless coolant temperature is high, A/C system pressure is low, A/C system pressure is high, wide open throttle, or high engine RPM.

When A/C-heater control panel is placed in A/C mode, a 12-volt signal is sent to VCM. When VCM receives this signal, VCM will ground A/C clutch relay control circuit to energize A/C relay. This is shown on scan tool as A/C REQUEST YES.

When an A/C request has been detected by VCM, VCM will ground A/C clutch relay control circuit. As a result, relay contacts close, allowing current to flow through relay to A/C compressor clutch. When A/C REQUEST has been detected by PCM, cooling fans will be turned on when A/C pressure is greater than a predetermined value.

Compressor Clutch Control Circuit Diagnosis

1. Install A/C manifold gauge set. Ensure A/C system is fully charged. Charge system if necessary and go to next step.
2. Start engine and allow it to reach normal operating temperature. Turn on A/C. If A/C compressor clutch engages, then disengages within 60 seconds, diagnose A/C-heater system. If operation is not as specified, go to next step.
3. Install scan tool. With A/C on, monitor A/C REQUEST. If scan tool displays A/C REQUEST as YES, go to next step. If scan tool does not display A/C REQUEST as YES, go to step 8).
4. Disconnect A/C compressor clutch harness connector. Connect a test light between harness connector terminals. If test light comes on, go to next step. If test light does not come on, go to step 12).
5. Check for faulty A/C compressor clutch harness connections. If a problem is found, go to next step. If no problem is found, go to step 7).
6. Repair faulty A/C compressor clutch wire harness connections. Go to step 27).
7. Replace A/C compressor clutch. Go to step 27).
8. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. Using a test light connected to ground, probe A/C request circuit (Dark Green/White wire) at VCM harness connector. If test light comes on, go to next step. If test light does not come on, go to step 11).
9. Check for poor VCM harness connections. If a problem is found, go to next step. If no problem is found, go to step 26).
10. Repair VCM harness connector. Go to step 27).
11. Repair open or short to ground in Dark Green/White wire between VCM and A/C control switch. Go to step 27).
12. Using a test light connected to ground, probe Dark Green wire at A/C compressor clutch harness connector. If test light comes on, go to next step. If test light does not come on, go to step 14).
13. Repair open in A/C compressor clutch ground circuit (Black wire) between harness connector and ground. Go to step 27).
14. Turn ignition on, engine off. Using scan tool, command A/C relay on. If A/C relay clicks, go to step 23). If A/C relay does not click, go to next step.
15. Disconnect A/C relay. Using a test light connected to ground, probe A/C relay cavity No. 86 (Pink wire), then cavity No. 87 (Orange wire). If test light comes on for both wires, go to step 17). If test light does not come on for both wires, go to next step.
16. Repair open or short to ground in affected circuit. Go to step 27).
17. Connect a test light between A/C relay cavity No. 86 (Pink wire) and cavity No. 85 (Dark Green/White wire). Using scan tool, command A/C relay on. If test light comes on, go to next step. If test light does not come on, go to step 19).
18. Replace A/C relay. Go to step 27).
19. Check A/C relay control circuit (Dark Green/White wire) for faulty connection at VCM harness connector. If a problem is found, go to next step. If no problem is found, go to step 21).
20. Repair faulty connection at VCM. Go to step 27).
21. Check for open in Dark Green/White wire between VCM and A/C relay. If a problem is found, go to next step. If no problem is found, go to step 26).
22. Repair open in Dark Green/White wire. Go to step 27).
23. Remove A/C relay. Using a fused jumper wire, jumper A/C relay cavity No. 87 (Orange wire) and cavity No. 30 (Dark Green wire) together. If A/C compressor clutch engages, go to next step. If A/C compressor clutch does not engage, go to step 25).
24. Replace A/C relay. Go to step 27).
25. Repair open or short to ground in A/C compressor clutch control circuit (Dark Green wire). Go to step 27).
26. Replace VCM. Go to next step.
27. Using scan tool, select DTC CLEAR INFO. Start engine and allow it to reach normal operating temperature. Select DTC SPECIFIC, then enter DTC number that was set. Operate vehicle within conditions that may have set this DTC. If DTC does not reset, go to next step. If DTC resets, go to step 2).
28. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any DTCs are displayed that have not been diagnosed, perform diagnosis for applicable DTC. See the «TESTS W/CODES - 6.5L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel-g-series) article. If no DTCs are displayed, system is okay.

COOLING FAN

The electric cooling fan is used for radiator and A/C condenser cooling. Cooling fan operates when A/C is on and when engine coolant temperature exceeds a specific value. One or more cooling fan relays may be used. Some RWD trucks and vans are equipped with an auxiliary electric cooling fan. The auxiliary electric cooling fan is not controlled by Powertrain Control Module (PCM). Auxiliary cooling fan information on "G" series van was not available at time of publication.

To help save diagnostic time, ALWAYS check for blown fuses or fusible links before proceeding with any testing. If fuses are blown, locate and repair short circuit before replacing fuses. Ensure all related relay and wire harness connections are clean and tight. Repair as necessary. See the WIRING DIAGRAMS article for component, terminal and wire color identification.

SCAN TESTER

A variety of information is transmitted through Data Link Connector (DLC). This data is transmitted at a high frequency which requires a Tech 1 Scan Tester (94-00101A), appropriate cartridge kit and vehicle interface module kit, or other scan tester for interpretation. Several scan testers (scan tools) are available for diagnostic work. Scan testers other than Tech 1 scan tester will function and provide information for diagnostic work.

COOLING FAN RELAY LOCATION

COMPONENT LOCATIONS

COMPONENT LOCATIONS

See also:
• BASIC TESTING - 6.5L DIESEL
• TESTS W/CODES - 6.5L
• TESTS W/O CODES - 6.5L
• ADJUSTMENTS - 6.5L DIESEL
• MODULES, MOTORS, RELAYS & SOLENOIDS
• FUEL SYSTEM
• IGNITION SYSTEM
• MISCELLANEOUS PCM CONTROLS
• COMPONENT LOCATIONS