Engine Controls - System/component Tests Chevrolet Chevy Van G10

INTRODUCTION

Before testing separate components or systems, perform all procedures listed in BASIC TESTING article. Since many computer controlled and monitored components will set a trouble code if they malfunction, it is also recommended that self-diagnosis be performed. See appropriate TESTS W/CODES 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 WIRING DIAGRAMS to isolate wiring harness shorts or opens.

A/C ON SWITCH SYSTEM TEST

1. Turn ignition switch to RUN position. Move mode selector switch to OFF position. With A/C control assembly connector connected, measure voltage between mode selector switch Dark Green wire and ground. For wiring schematics, see mini-schematics in A/C CLUTCH under «MISCELLANEOUS ECM CONTROLS»(/chevrolet/chevy-van-g10/1985-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__miscellaneous-ecm-controls) in this 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 Dark Green wire from selector switch to fuse for an open circuit.
3. Check voltage between mode selector Dark Green wire and ground. Voltage should not be present. If voltage was 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.

COOLANT TEMPERATURE SENSOR (CTS)

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

CTS RESISTANCE VALUES

KNOCK SENSOR

1. Leave knock sensor harness connector connected. Using a voltmeter, backprobe knock sensor connector. 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 in this article and appropriate TESTS W/CODES article.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

1. A malfunction in the MAP sensor circuit should set a related code in ECM memory. If a code is present, see appropriate TESTS W/CODES 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, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a Scan tester connected to the ALDL connector. Voltage should be as specified in «MAP SENSOR VOLTAGE RANGE»(/chevrolet/chevy-van-g10/1985-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. If MAP sensor voltage is as specified, go to next step. If voltage is not as specified, check for 5-volt reference supplied to sensor. Check harness integrity. If no problems are evident, replace MAP sensor.
3. Using a hand-held vacuum pump, apply 10 in. Hg to MAP sensor and note voltage change. Voltage should drop to about 1.0-1.5 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.

Scheme 82

MAP SENSOR VOLTAGE RANGE

MANIFOLD AIR TEMPERATURE (MAT) SENSOR (2.5L ONLY)

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

MAT SENSOR RESISTANCE

OXYGEN SENSOR (O2)

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect a DVOM between Purple lead of oxygen sensor and ground. Place meter on the 2-volt scale. Voltmeter reading should increase to greater than .8 volt.
2. Using another DVOM on the 20-volt scale. Connect voltmeter in series between Purple wire from the ECM and the positive post of battery. Reading on voltmeter connected to oxygen sensor should decrease to a low voltage (less than .3 volt). If reading does not change as specified, replace O2 sensor.
3. If a second DVOM is not available, install short jumper in Purple wire from the ECM. Hold jumper in one hand and touch positive post of battery with other hand to cause oxygen sensor to produce less than .3 volts. For additional testing procedures, see appropriate TESTS W/CODES article.

P/N SWITCH

Disconnect P/N switch (located on transmission) harness connector. Connect ohmmeter between the P/N switch terminals. (Scheme 83) Continuity should be present only when gear shift selector is in Park or Neutral. If continuity is not present, check P/N switch adjustment or replace defective P/N switch.

Scheme 83

POWER STEERING PRESSURE SWITCH (2.5L ONLY)

Disconnect P/S pressure switch harness connector. Connect ohmmeter between P/S pressure switch terminals. Start engine. With no-load on power steering, continuity should not be present. Turn steering wheel to full stop, continuity should now be present. If readings are not as specified, replace defective P/S pressure switch.

THROTTLE POSITION SENSOR (TPS)

1. Install jumper wires to enable connection of a DVOM in parallel between TPS harness connectors. Connect DVOM positive lead to Dark Blue wire terminal. Connect negative lead to Black wire terminal. (Scheme 84)
2. Turn ignition on, engine off. 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, adjust or replace TPS. See ON-VEHICLE ADJUSTMENTS article.
3. A malfunction in the TPS circuit should set a related trouble code. For further information, see appropriate TESTS W/CODES article. Also see TPS adjustment procedure in ADJUSTMENTS article.

Scheme 84

VEHICLE SPEED SENSOR (PM GENERATOR TYPE)

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

A/C RELAYS

See MISCELLANEOUS ECM CONTROLS in this article.

COLD ADVANCE RELAY (6.2L DIESEL)

See DIESEL COLD ADVANCE SYSTEM CHECK under FUEL SYSTEM (DIESEL) in this article.

DOWNSHIFT CONTROL RELAY (THM 400)

1. Disconnect wiring harness connector to downshift control relay. Measure resistance between relay terminals "D" and "F". (Scheme 85) Resistance should be 20 ohms. If resistance is not as specified, replace downshift control relay.
2. Connect ohmmeter between relay terminals "A" and "E". (Scheme 85) No continuity should be present. If continuity is present, replace shorted downshift control relay.

Scheme 85

FUEL PUMP RELAY

1. Disconnect fuel pump relay. Refer to I - SYSTEM/COMP LOCATION article. Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see appropriate wiring diagram in WIRING DIAGRAMS.
2. Using an ohmmeter, check continuity between fuel pump relay power and fuel pump relay drive terminals. Continuity should exist. If continuity does not exist, fuel pump relay is defective.
3. 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.
4. If fuel pump runs, check for faulty connections to relay or replace defective relay. To locate fuel pump test connector, refer to I - SYSTEM/COMP LOCATION article.

Scheme 86

SOLENOIDS

Note. All ECM controlled solenoids should have at least 20 ohms of resistance.

Canister Purge Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS in this article.

Idle Air Control (IAC) Motor

See IDLE CONTROL SYSTEM in this article.

FUEL SYSTEM (GASOLINE)

Note. For fuel system pressure testing, see BASIC TESTING article.

FUEL PRESSURE REGULATOR (TBI)

Fuel pressure regulator is mechanically controlled by internal spring pressure. Regulator is adjusted at factory and is not serviceable. If fuel pressure is too low, check fuel filter, fuel pump pressure and volume. If fuel pressure is too high, check for restricted fuel tank return line. If no faults are found and pressure is too high or too low, replace fuel pressure regulator.

See RELAYS, SOLENOIDS, MOTORS & MODULES in this article.

FUEL PUMP RELAY BY-PASS PROCEDURE

If fuel pump will not energize, relay may be by-passed to test fuel pump. Turn ignition off. Using a fused jumper wire, apply battery voltage to fuel pump test connector. Fuel pump should turn on. For fuel pump test connector location, refer to I - SYSTEM/COMP LOCATION article.

FUEL INJECTOR(S)

Disconnect fuel injector harness connector. Measure resistance across injector terminals. Resistance should be as specified. See FUEL INJECTOR RESISTANCE table.

FUEL INJECTOR RESISTANCE

OXYGEN SENSOR

See ENGINE SENSORS & SWITCHES in this article.

IDLE AIR CONTROL (IAC) MOTOR (2.5L)

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". Resistance should be 40-80 ohms. (Scheme 87) If okay, go to next step. If resistance is not as specified, replace IAC motor.
2. Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC motor.

Note. Testing Idle Air Control (IAC) motor requires a Scan tester capable of cycling ECM output devices. Flow charts in the TESTS W/CODES articles may refer to the Tech 1 tester, General Motors' version of this tester.

Scheme 87

FUEL SYSTEM (DIESEL)

Note. The 6.2L light duty emissions engine (LH6) uses the Diesel Electronic Control (DEC) system. For complete system testing and diagnosis of DEC system, see TESTS W/CODES article.

NORMAL GLOW PLUG CIRCUIT OPERATION

A normal functioning system should operate as follows

1) With ignition switch in the ON position, engine not running and at room temperature, glow plugs are on for 4-to-6 seconds, then off for about 4.5 seconds. Following this on and off cycle, glow plugs are on for about 1.5 seconds and off for about 4.5 seconds. The glow plugs continue to cycle on-and-off in this time sequence for about 20 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 the ignition switch is returned from the 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-g10/1985-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__normal-glow-plug-circuit-operation) , ensure glow plug system is correctly installed. Check that all connectors are properly attached, clean and tight. Inspect engine harness ground connection. Ensure nut securing 4-wire connector at controller is tightened to 96 INCH lbs. (11 N.m), with connector fully seated and latched.
2. Ensure controller copper stud upper nuts are tightened to 96 INCH lbs (11 N.m). Do not tighten lower nuts. Ensure temperature switch connector in water crossover near front of engine is tightened to 48 INCH lbs. (5.4 N.m). Inspect WAIT lamp on instrument panel for tight connection and operation.

INHIBIT SWITCH (BLACK CAP)

1. Remove connector from inhibit switch when engine temperature is below 100°F (38°C). Inhibit switch is located in water crossover near front of engine. Set ohmmeter on low range. Test across switch terminals. Switch should be closed (a reading of less than 1.0 ohm on meter.)
2. Test terminals to ground with a test light or ohmmeter on high range. Light should be off. Meter should show greater than 1.0 megohm. Replace switch if results are not as specified.
3. Disconnect plug from switch terminals when engine is above 125°F (52°C). Change ohmmeter setting to highest scale or use a self-powered test light. Test across switch terminals. Test from each terminal to ground. Switch should be open (test light off or high ohm reading of greater than 1.0 megohm on meter). Replace switch if it is closed. When installing replacement switch, tighten to 17 ft. lbs. (23 N.m).

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 greater 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 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 turned ignition off. Check cranking speed is at least 100 RPM.

1) With ignition switch off, measure voltage at battery stud (single wire) on glow plug. (Scheme 88) If no voltage is present, repair battery to glow plug controller circuit.

2) If no voltage is present in step 1), disconnect harness from all glow plugs. Using an ohmmeter, measure resistance between glow plug terminals and engine block. Replace glow plug if resistance is greater than 2 ohms. Reconnect all glow plugs before continuing with diagnosis.

3) If voltage was present in step 1), turn ignition off and measure voltage at glow plug feed stud (twin lead) on glow plug controller. If battery voltage is now present, relay contacts are shorted. Replace controller and all glow plugs.

4) With all glow plugs reconnected, place ignition switch in RUN position. Remove controller connector and check voltage at harness connector terminal "D". (Scheme 88)

5) If no voltage is present, repair open in ignition feed circuit to controller. If voltage is present, measure resistance between terminal "E" of connector and engine block (ground). If measurement is greater than one ohm, repair ground circuit to controller.

6) With ground circuit working properly in step 4), measure resistance between terminals "C" and "E" of connector. (Scheme 88) If reading is greater than 2 ohms, go to next step. If reading is less than 2 ohms, go to step 8).

7) If reading in step 5) is greater than 2 ohms, remove connector from temperature inhibit switch and measure continuity between the 2 terminals on switch. Switch is open above 125°F (51.5°C). If reading is less than one ohm, repair glow plug circuit to controller. If reading is greater than one ohm, replace temperature inhibit switch and return to step 6).

8) If reading in step 5) was less than 2 ohms, reconnect controller harness connector and ensure complete engagement. Connector locking latch should click over controller locking tab. With controller connector harness correctly connected, measure voltage at glow plug feed stud (twin lead) on glow plug controller, while turning ignition switch from OFF position to RUN position.

9) If no voltage is present, replace glow plug controller. If battery voltage is present, measure 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 8), repair glow plug feed circuit to glow plugs. If battery voltage is present and instrument panel GLOW PLUG light does not come on, locate and repair bulb or circuit.

Scheme 88

DIESEL COLD ADVANCE SYSTEM CHECK

With ignition on and coolant temperature below 80°F (27°C), the ECM grounds circuit No. 905 to the cold advance relay. Grounding circuit No. 905 turns on cold advance relay, to supply 12 volts to the cold advance solenoid (in the injection pump), and glow plug controller. The cold advance solenoid is now energized, which causes injection pump timing to be advanced about 4 degrees.

COLD ADVANCE RELAY

1. Disconnect harness connector to cold advance relay. Using an ohmmeter, check resistance between relay terminals "D" and "F". (Scheme 89) Continuity should be present or a resistance of 20 ohms. If not, replace cold advance relay.
2. Using an ohmmeter, check continuity between relay terminals "A" and "E". (Scheme 89) Continuity should not be present. If continuity is present, replace grounded cold advance relay.

Scheme 89

GLOW PLUG CONTROLLER

1. Ensure coolant temperature is below 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 the engine starts. Return ignition switch to RUN position. Glow plugs should cycle on at least once.
2. If glow plugs do not cycle, disconnect controller connector (controller is located on top, rear of valve cover). Connect a 12-volt test light between Purple/White wire terminal of harness connector (terminal "B") and ground. With ignition switch in RUN position, test light should be off. Test light should glow when engine is cranked. (Scheme 88)
3. If test light does not glow as specified, repair short or open in engine harness Purple/White wire. If test light operates properly but glow plugs did not cycle, replace controller.

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, pump must be replaced.

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 36142) to remove and replace injection nozzle. Attach socket to 30mm hex portion of nozzle. Failure to do so will result in damage to the 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 the lowest limit of 1500 psi (105 kg/cm 2 ). Replace any injector nozzle which does not meet lowest acceptable pressure. Release tester pressure.

LEAKAGE TEST

1. Open tester shutoff valve 3/4 to 1 3/4 turns from a 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 drop off within a 10 second period. Replace injector nozzle if drop of test fluid drops from tip during the 10 second period. (Scheme 90) Release tester pressure.

Scheme 90

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, the injector nozzle is acceptable.

1) Close tester shutoff lever at pressure gauge. Slowly depress lever and note whether chatter can be heard. If no chatter is heard, increase speed of lever movement until it reaches a point where 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 which does not chatter.

SPRAY PATTERN TEST

The injector nozzles used with this system have several features which 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 BASIC TESTING article.

ELECTRONIC SPARK CONTROL (ESC) CIRCUIT (EXCEPT 2.5L)

1. An open or short circuit on the ESC wire to the ECM will cause a loss of the 12-volt ESC controller signal. This will cause the ECM to fully retard ignition timing.
2. If a Scan tester is available, connect it to the ALDL connector. Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on Scan tester.
3. If a Scan tester is not available, connect a DVOM to the ECM ESC signal terminal. With engine idling, 12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at ECM terminal should drop to zero volts, and return when knock signal ceases.
4. If signal does not respond as described, check knock sensor signal to controller signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR in ENGINE SENSORS & SWITCHES in this article.

ELECTRONIC SPARK TIMING (ALL ENGINES)

An open or short circuit to ground in the Electronic Spark Timing (EST) or by-pass circuits will confirm Code 42 and that the fault causing the code is present. Refer to SELF-DIAGNOSTICS article.

AIR PUMP

Accelerate engine to approximately 1500 RPM and observe airflow from hoses. If airflow increases as engine is accelerated, pump is working properly. If airflow does not increase, check hoses, pump belt tension, leaky valves or defective air injection pump.

CHECK VALVE

Detach check valve and blow through valve in direction of check valve flow (to cylinder head). Attempt to suck back. Replace valve if airflow is allowed against the direction of flow.

ELECTRONIC AIR CONTROL (EAC) SOLENOID

1. Turn ignition on, engine off. Disconnect EAC solenoid connector. Connect test light between solenoid connector terminals. (Scheme 91) If test light comes on, check for grounded wire from solenoid to ECM. If wire is not grounded, replace ECM. If test light did not turn on, go to next step.
2. Ground ALDL diagnostic connector. If test light comes on, check for faulty EAC solenoid connector. If connector is okay, replace EAC valve. If test light did not turn on, connect test light between harness terminal "A" to ground. (Scheme 91) If test light still did not turn on, check for open in fuse or wire to ignition.
3. If test light came on, check for open in wire from solenoid to ECM. If wire is okay, check EAC solenoid resistance. If resistance is less than 20 ohms, replace EAC solenoid and perform ECM quad-driver check. If EAC solenoid resistance is greater than 20 ohms, replace ECM only.

Scheme 91

SYSTEM TEST

Start and run engine to normal operating temperature. With engine at idle, RPM should drop as EGR valve is opened by pushing up on underside of EGR diaphragm.

EGR CONTROL SOLENOID

1. Disconnect EGR solenoid electrical harness connector and vacuum hoses. Connect a hand-held vacuum pump to solenoid vacuum source port. Connect vacuum gauge to solenoid EGR port. Pump up vacuum pump. Vacuum should not be present at port to EGR valve.
2. Activate EGR solenoid with a 12-volt power supply. Vacuum should now be present or registered at vacuum gauge. Solenoid should have at least 20 ohms of resistance.

NEGATIVE BACKPRESSURE EGR VALVE

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 20 seconds. If not, replace EGR valve.

VAPOR CANISTER

1. Install a short length of hose to lower port of purge valve. Blow into hose. Little or no air should pass into canister (a small amount of air will pass if the canister has a constant purge hole).
2. Using a hand-held vacuum pump, apply 15 in. Hg to vacuum control (upper) port. Vacuum should hold for 20 seconds. If not, replace canister.
3. With vacuum still applied, again try to blow through hose connected lower port. An increased flow of air should be observed. If not, replace canister.

FUEL TANK PRESSURE CONTROL VALVE

Install a short piece of hose on valve inlet tube (fuel tank side) and blow into hose. Diaphragm should pop open and air should pass through valve. If valve does not open, fuel tank pressure control valve should be replaced.

PCV

Required Service - The PCV system may require service for obstructions if any of the following conditions exist

1. Rough Idle
2. Stalling or Slow Idle Speed
3. Oil Leaks
4. Oil in Air Cleaner
5. Sludge in Engine

A PCV leaking valve or hose could cause

1. Rough Idle
2. Stalling
3. High Idle Speed

If engine idles roughly, check for clogged PCV valve, plugged or broken hoses BEFORE adjusting idle. Check correct PCV valve application to ensure the correct valve is fitted. Replace PCV valve if required.

CHECKING PCV VALVE FUNCTION

1. Remove PCV valve from rocker cover. Run engine at idle. Place thumb over open end of valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary.
2. Turn engine off. Remove PCV valve. Shake valve and listen for rattle of check valve inside. If a clear rattle is not heard, replace PCV valve.
3. Visually inspect valve for varnish or deposits which may make PCV valve operation sticky, restricted or cause incomplete seating of valve. Replace if necessary.
4. An engine must be sealed for the PCV system to function as designed. If leakage, sludging or dilution of oil is noted and the PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
5. An engine operating without any crankcase ventilation can be damaged so it is important to replace PCV valve and air cleaner breather at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

CRANKCASE DEPRESSION REGULATOR (CDR)

To test CDR valve, connect one hose of a water manometer to the engine oil dipstick tube. Leave other hose of manometer open to atmosphere. Install air cleaner and run engine. CDR valve specification in 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 20 seconds. If not, replace EGR valve.

EXHAUST PRESSURE REGULATION (EPR) SYSTEM

Note. For testing of the EPR system, see appropriate chart in TESTS W/CODES article.

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 all is okay, replace pump.

MISCELLANEOUS ECM CONTROLS

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

A/C CLUTCH RELAY

1. Disconnect A/C clutch relay harness connector. Using proper mini-schematic and an ohmmeter, check continuity between A/C clutch relay winding terminals. Continuity should exist. Check continuity between clutch drive circuit terminals of relay. Continuity should not exist. (Scheme 92)-14.
2. Using jumper wires, apply ground and battery voltage to relay winding. Continuity should now exist between clutch drive circuit terminals of relay. Replace A/C clutch relay if readings are not as specified.

Scheme 92

Scheme 93

Scheme 94

Scheme 95

COOLING FAN (3.1L ONLY)

Note. For additional information on electric cooling fans, see ELECTRIC COOLING FANS article in ENGINE COOLING.

COOLING FAN RELAY

1. Disconnect cooling fan relay harness connector. Using an ohmmeter, check continuity of relay winding. (Scheme 96) Continuity should exist. Check continuity across power delivery terminals of relay. With relay not energized, no continuity should exist.
2. With ohmmeter still attached to power delivery terminals of relay, apply battery voltage and ground to energize relay winding. Continuity should now be present between cooling fan relay power delivery terminals. Replace cooling fan relay if readings are not as specified.

COOLING FAN MOTOR

Disconnect cooling fan motor harness connector. Apply battery voltage to one of the fan motor terminals and jumper the other terminal to ground. Fan motor should activate. If fan motor does not activate, replace faulty fan motor.

Scheme 96

TORQUE CONVERTER CLUTCH (TCC) SOLENOID

Disconnect harness connector to TCC solenoid. Measure resistance between TCC solenoid terminals "A" and "D". Solenoid resistance should be greater than 20 ohms. (Scheme 95)and (Scheme 96).

Scheme 97

Scheme 98

Note. Some solenoids have an internal pressure switch in series with the solenoid winding and will not show continuity until transmission hydraulic pressure is applied. (Scheme 99)

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 terminals "A" and "D" of converter clutch harness. 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 ECM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM ECM.

CONVERTER LOCK-UP SIGNAL FROM ECM

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. (Scheme 99) Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty ECM connector or ECM. On some models, lock-up signal may be checked at ALDL terminal "F" instead of at ECM terminal.

Scheme 99

SHIFT LIGHT (MANUAL TRANSMISSION)

1. These tests assume a shift light problem exists. Use this procedure only if the light will not illuminate, or illuminates all the time.
2. Turn ignition on, with engine off. Note shift light. Shift light should not be on. If light is on, check for a short to ground between the bulb and ECM, or a bad ECM.
3. With ignition on and engine off, ground "test" terminal of ALDL connector. SERVICE ENGINE SOON light should start to flash and shift light should come on. If light comes on, go to next step. If SERVICE ENGINE SOON light does not flash, perform DIAGNOSTIC CIRCUIT CHECK as described in BASIC TESTING article.
4. If shift light does not come on, ground Tan/Black wire at ECM terminal B7 using a jumper wire. If light still does not come on, check for blown GAUGES fuse, blown bulb or open circuit between fuse and ECM. If light came on when grounding terminal B7 with a jumper wire, problem is a bad ECM connection or bad ECM.

Scheme 100

See also:
• MISCELLANEOUS ECM CONTROLS
• MAP SENSOR VOLTAGE RANGE
• DIESEL COLD ADVANCE SYSTEM CHECK
• NORMAL GLOW PLUG CIRCUIT OPERATION