Engine Controls - System/component Tests - 6.5l Diesel Chevrolet Cab & Chassis K2500

MODEL IDENTIFICATION

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

MODEL IDENTIFICATION

TERMINOLOGY

Due to Federal government requirements, manufacturers may use names and acronyms for systems and components different than those used in previous years. The following table will help eliminate confusion when dealing with these components and systems. Only relevant components and systems whose names have changed from current General Motors Corp. terminology have been listed.

SAE TERMINOLOGY

INTRODUCTION

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

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

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.

The following table provides the location of commonly used diagnostic information. These former "A" and "C" charts are now written in text and inserted into the new Engine Performance workflow. To familiarize yourself with the Engine Performance workflow, see the AA - USING THIS SECTION (GENERAL HELP INFORMATION) article in this section.

GENERAL MOTORS "A" & "C" CHART REFERENCE

TURBOCHARGER

Note. No turbocharger testing information not available at time of publication. For symptom diagnosis see TROUBLE SHOOTING - NO CODES article or appropriate G - DIESEL TESTS W/ CODES article in this section below.

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

CONTROL UNIT

Note. To perform the following ground and power tests, use appropriate wiring diagram at the end of this article.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on ECM ground terminals. Resistance should be zero ohms. If not, repair open to ground.
2. Using a DVOM, 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 greater than one volt, check for open, corrosion or loose connection on ground circuit.

Power Circuits

1. Using a voltmeter, check for battery voltage between ECM 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 ECM terminal and power source.
2. Turn ignition on. Using a voltmeter, check for battery voltage between ECM 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 ECM terminal. If okay, check for a defective ignition switch.
3. Connect voltmeter between ground and ECM 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 ECM terminal. If fuse or fusible link is okay, check for an open in wire between ignition switch and ECM 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 OFF position. With A/C control assembly 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/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel__miscellaneous-ecm-controls) .
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 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 Dark Green 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 appropriate TESTS W/CODES article in this section below. 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.

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

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 appropriate TESTS W/CODES article in this section below. 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.

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

IAT SENSOR RESISTANCE

Manifold Absolute Pressure (MAP) Sensor

1. MAP sensor circuit malfunction should set a related code in ECM memory. (Scheme 232) If a code is present, see appropriate TESTS W/CODES article in this section below. 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. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series) G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)
2. With ignition on and engine off, check MAP sensor parameter using a scan tester connected to Data Link Connector (DLC). Voltage should be as specified. See «MAP SENSOR VOLTAGE RANGE»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel) table.
3. 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.
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

Scheme 232

Oxygen Sensor

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect DVOM between Purple lead of oxygen sensor and ground. Place DVOM on 2-volt scale.
2. Using another DVOM on 20-volt scale, connect voltmeter in series between Purple wire from ECM and positive post of battery. This will simulate a rich condition, causing ECM to respond by leaning mixture. Reading on voltmeter connected to oxygen sensor should decrease to less than .3 volt.
3. Move voltmeter lead from positive battery post to negative battery post. This will simulate a lean condition, causing ECM to respond by richening mixture. Reading on voltmeter 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, install a jumper in Purple wire from ECM. 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 appropriate TESTS W/CODES article in this section below. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series) G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

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.

Park/Neutral (P/N) Switch

Disconnect P/N switch (located on transmission) harness connector. Connect ohmmeter between P/N switch terminals. (Scheme 233) 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 233

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 234)
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, replace TP sensor.
3. TP sensor circuit malfunction should set a related trouble code. For further information, see appropriate TESTS W/CODES article in this section below. Also see TP sensor adjustment in ADJUSTMENTS - 6.5L DIESEL article in this section. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series) G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

Scheme 234

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 (greater 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 appropriate TESTS W/CODES article in this section below.

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

A/C Relays

See MISCELLANEOUS ECM 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/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel) near end of this article. (Scheme 235) Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see «WIRING DIAGRAMS»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel) at the end of this article.
3. 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.
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/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel).

Scheme 235

SOLENOIDS

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

Electronic Air Control (EAC) Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

EGR Control Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Torque Converter Clutch (TCC) Solenoid

See MISCELLANEOUS ECM CONTROLS .

FUEL SYSTEM

Note. For complete system testing and diagnosis, see TESTS W/CODES article in this section as listed below.

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

IMPORTANT PRELIMINARY CHECKS

Ensure you have performed the On-Board Diagnostic System Check and determined that

1. The Control Module and MIL (Malfunction Indicator Lamp) are operating correctly
2. There are no Diagnostic Trouble Codes (DTCs) stored, or a DTC exists but without a MIL.

See

BASIC TESTING - 6.5L DIESEL

article.

Visual and Physical Checks

The visual and physical checks are very important. The checks can lead to correcting a problem without further checks which may save valuable time.

1. Check the Control Module grounds for being clean, tight and in their proper location.
2. Check the vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
3. Check thoroughly for any type of leak or restriction.
4. Check for air leaks at all the mounting areas of the intake manifold sealing surfaces.
5. Check the wiring for the following items: - Proper connections Pinches Cuts

Symptom

1. Verify the customer complaint.
2. Locate the correct symptom under «SYMPTOMS»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-tests-wo-codes-65l-diesel__symptoms) in TESTS W/O CODES article.
3. Check the items indicated under that symptom

HARD START

Note. For additionao symptom diagnosis, see SYMPTOMS in TESTS W/O CODES article.

Note. Definition: The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but immediately dies

Preliminary Checks

1. Refer to «IMPORTANT PRELIMINARY CHECKS»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel__important-preliminary-checks) .
2. Make sure the driver is using the correct starting procedure.

Sensor Checks

1. Check the Engine Coolant Temperature (ECT) sensor using the scan tool to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5° greater or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or the sensor itself.

Fuel System Checks

1. Check the Supply to injection pump. Refer to «BASIC TESTING - 6.5L DIESEL»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-basic-testing-65l-diesel)
2. Check for air in fuel system. article
3. Check the fuel return from injection pump. Refer to «BASIC TESTING - 6.5L DIESEL»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-basic-testing-65l-diesel) article
4. Check engine shut-off solenoid operation.
5. Check the fuel injection nozzles. See «INJECTORS»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel)
6. Check the fuel tank cap vent.
7. Check for an internal injection pump problem.

Electrical System Checks

1. Check glow plug operation. Refer to «NORMAL GLOW PLUG CIRCUIT OPERATION»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel__normal-glow-plug-circuit-operation)
2. Check for slow cranking speed on scan tool.

Air Intake System Checks

1. Check the air cleaner and air intake ducts for a restriction.
2. Check for a restriction in turbo charger inlet duct
3. Check for a restriction in the intake manifold

Exhaust System Check

1. Check the exhaust system for possible restriction

Engine Mechanical Checks

1. Check the engine for the following: Improper valve timing Low compression Bent pushrods Worn rocker arms Broken or weak valve springs Worn camshaft lobes

Additional Checks

1. Check for no crank signal on scan tool
2. Check the Service Bulletins for control module software updates.

Scheme 236

NORMAL GLOW PLUG CIRCUIT OPERATION

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 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 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/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-65l-diesel__normal-glow-plug-circuit-operation) , ensure glow plug system is correctly installed. Ensure 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 light on instrument panel for tight connection and operation.

INHIBIT SWITCH (BLACK CAP)

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

GLOW PLUG CONTROLLER

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 controller (controller is located on top rear of valve cover). Connect a 12-volt test light between Pink/Black wire terminal of harness connector (terminal "A") and ground. (Scheme 236) With ignition switch in RUN position, test light should be off. Test light should glow when engine is cranked.
3. If test light does not glow as specified, repair short or open in engine harness Pink/Black wire. If test light operates properly but glow plugs do 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, 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-36142) 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 237) Release tester pressure.

Scheme 237

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.

Crankcase Depression Regulator (CDR)

To test CDR valve, connect one hose of a water manometer to engine oil dipstick tube. (Scheme 239) 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.

Scheme 238

Scheme 239

Scheme 240

Scheme 241

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 ECM CONTROLS

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

Disconnect harness connector to TCC solenoid. Measure resistance between TCC solenoid terminals. (Scheme 242) Solenoid resistance should be greater than 20 ohms.

Scheme 242

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. (Scheme 242) 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 below.

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 242) 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 Data Link Connector (DLC) terminal "F" instead of at ECM terminal.

Shift Light (Manual Transmission)

Note. These tests assume a shift light problem exists. Use this procedure only if the light will not illuminate, or illuminates all the time.

1. 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 bulb and ECM or for bad ECM.
2. With ignition on and engine off, ground test terminal "B" of Data Link Connector (DLC). Malfunction Indicator Light (MIL) should start to flash and shift light should come on. If MIL comes on, go to next step. If MIL does not flash, perform DIAGNOSTIC CIRCUIT CHECK as described in «BASIC TESTING - 6.5L DIESEL»(/chevrolet/cab-chassis-k2500/1989-2000/remont/testing-diagnostics/#engine-controls-basic-testing-65l-diesel) article in this section.
3. If shift light does not come on, ground Tan/Black light driver wire at ECM terminal using a jumper wire. (Scheme 243)or (Scheme 244). If light still does not come on, check for blown GAGES fuse, blown bulb or open circuit between fuse and ECM. If light comes on when grounding ECM terminal with a jumper wire, problem is a bad ECM connection or bad ECM.

Scheme 243

Scheme 244

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. (Scheme 245) Continuity should exist. Check continuity between clutch drive circuit terminals of relay. Continuity should not exist.
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 continuity does not exist.

COOLING FAN (C-12)

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

Cooling Fan Relay

1. Disconnect cooling fan relay harness connector. Using an ohmmeter, check continuity of relay winding. (Scheme 246) Continuity should exist. Check continuity across power delivery terminals of relay. With relay not energized, continuity should not exist.
2. With ohmmeter still attached to power delivery terminals of relay, apply battery voltage and ground to energize relay winding. Continuity should now exist between cooling fan relay power delivery terminals. Replace cooling fan relay if continuity does not exist.

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.

Note. For a more specific system testing, refer to the following C-10 or C-12 diagnostic charts. If any chart other than a C-10 or C-12 chart is referenced, see appropriate TESTS W/CODES article in this section below.

1. G - TESTS W/CODES - 6.5L DIESEL (for "C" & "K" Series)
2. G - TESTS W/CODES - 6.5L DIESEL (for "G" & "P" Series)

A/C REQUEST SIGNAL CIRCUIT DIAGNOSIS

Turning on A/C system supplies battery voltage to A/C compressor clutch and Powertrain Control Module (PCM). PCM responds by increasing idle speed. PCM does not control A/C compressor clutch. If A/C compressor clutch is malfunctioning, repair basic A/C system problem. If A/C system is operating properly and idle speed drops too low when A/C compressor turns on or flares too high when A/C compressor turns off, check for an open A/C signal circuit to PCM. (Scheme 245) If circuit is okay, repair faulty PCM connection or replace faulty PCM.

Scheme 245

Scheme 246

Scheme 247

Scheme 248

Scheme 249

Wiring Diagram For Blazer, Pickup, Sierra, Suburban & Yukon With M/T (1 Of 2). Scheme 250

Wiring Diagram For Blazer, Pickup, Sierra, Suburban & Yukon With M/T (2 Of 2). Scheme 251

Wiring Diagram For Blazer, Pickup, Sierra, Suburban & Yukon With 4L60-E (1 Of 2). Scheme 252

Wiring Diagram For Blazer, Pickup, Sierra, Suburban & Yukon With 4L60-E (2 Of 2). Scheme 253

Wiring Diagram For Blazer, Pickup, Sierra, Suburban & Yukon With 4L80-E (1 Of 2). Scheme 254

Wiring Diagram For Blazer, Pickup, Sierra, Suburban & Yukon With 4L80-E (2 Of 2). Scheme 255

Wiring Diagram For "P" Series Commercial Van - VIN F With 4L80-E (1 Of 2). Scheme 256

Wiring Diagram For "P" Series Commercial Van - VIN F With 4L80-E (2 Of 2). Scheme 257

Wiring Diagram For "P" Series Commercial Van - VIN Y With 4L80-E. Scheme 258

Wiring Diagram For Van - VIN P With 4L60-E (1 Of 2). Scheme 259

Wiring Diagram For Van - VIN P With 4L60-E (2 Of 2). Scheme 260

Wiring Diagram For Van - VIN Y With 4L80-E. Scheme 261

See also:
• BASIC TESTING - 6.5L DIESEL
• SYMPTOMS
• MODEL IDENTIFICATION
• MISCELLANEOUS ECM CONTROLS
• IMPORTANT PRELIMINARY CHECKS
• NORMAL GLOW PLUG CIRCUIT OPERATION