Engine Controls - System/component Tests: Diagnosis Chevrolet Pickup K1500

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 (Dark Green/White on "L", "M" & "U" Series) and ground. For wiring schematics, see mini-schematics in A/C CLUTCH under «MISCELLANEOUS ECM CONTROLS»(ref-19439-S10796272722001010200000) .
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 or Dark Green/White wire and ground. Voltage should not be present. If voltage is present, replace mode selector switch.

C-2, PFI Injector Balance Test

The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. An injector with a pressure drop of 1.5 psi (.11 kg/cm 2 ) or more, greater than or less than other injectors, should be considered faulty.

Note. Allow engine to cool down to avoid irregular readings due to "hot soak" fuel boiling. To prevent flooding, the PFI INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.

1. With ignition off, connect Fuel Pressure Gauge (J-34730-1) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J-34730-3) to one of the injectors.
2. Follow manufacturer's instructions when installing adapter harness. Ignition should be turned off at least 10 seconds to complete ECM shutdown cycle.
3. Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
4. Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize tester one time and note pressure drop at lowest point.
5. Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
6. Repeat step 4) on each injector and compare pressure drop. Recheck injectors not within pressure drop range. Replace injector(s) failing second check.
7. If injectors are all okay, plug in harness connectors and review SYMPTOMS in TESTS W/O CODES article in this section.

PRELIMINARY GLOW PLUG DIAGNOSIS

1. If system does not operate as described in 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.

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 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, 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.

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.

CHART C-10, A/C CLUTCH CONTROL CIRCUIT DIAGNOSIS 2.5L & 2.8L

ECM controls A/C clutch engagement to improve idle quality and performance by delaying A/C clutch engagement until idle speed is increased, disengages clutch when idle speed is too low, and smooths cycling of compressor by providing additional fuel instant A/C clutch is engaged.

Turning on A/C switch supplies battery voltage to clutch control relay terminal "B" and ECM terminal B8. After a delay of about .5 seconds, ECM will ground ECM terminal A4, closing control relay and engaging A/C compressor clutch.

Note. Test numbers refer to numbers on diagnostic charts.

1. 3) Checks for faulty cycling switch. Solenoids and relays are turned on and off by ECM, using "drivers". Each driver is a part of a group of 4, called quad-drivers. Failure of one driver can damage any other driver in set. Solenoid and relay coil resistance should be greater than 20 ohms.

Diagnostic Aids

Check resistance of each ECM controlled relay or solenoid coil before replacing ECM. See CONTROL UNIT under COMPUTERIZED ENGINE CONTROLS. Replace any relay or solenoid with a resistance of less than 20 ohms.

Scheme 91

C-10, A/C CLUTCH CNTRL CKT DIAGNOSIS - 3.1L (FRONT A/C ONLY)

A/C clutch control circuit is ECM controlled to delay A/C clutch engagement approximately 8 seconds after engine is started. This allows Idle Air Control (IAC) motor to adjust engine RPM before A/C clutch engages. ECM also causes relay to disengage A/C clutch during Wide Open Throttle (WOT) operation or if engine is overheating. A/C clutch control relay is energized when ECM provides a ground path for circuit No. 459. Low pressure switch will open if A/C pressure is less than 40 psi (2.8 kg/cm 2 ); high pressure switch will open if A/C pressure is approximately 440 psi (30.9 kg/cm 2 ).

Vehicles equipped with rear A/C option use a pressure cycling switch instead of a low pressure switch. A/C pressure cycling switch closes at pressure greater than 43-49 psi (3.0-3.4 kg/cm 2 ) and opens at pressure of less than 23-25 psi (1.6-1.8 kg/cm 2 ). An A/C refrigerant fan request switch opens to request fan(s) on, when A/C refrigerant pressure exceeds approximately 200 psi (14.1 kg/cm 2 ).

Note. Test numbers refer to numbers on diagnostic charts.

1. ECM will only energize A/C relay when engine is running. This test determines if relay or circuit No. 459 is faulty.
2. A/C compressor clutch should apply if the following conditions are met: On front A/C option only, low and high pressure switch must be closed so A/C request (12 volts) will be present at ECM. On rear A/C option only, A/C mode is requested via high pressure and pressure cycling switches, 12 volts is supplied to relay coil through high pressure switch. As compressor reduces evaporator pressure to approximately 25 psi (1.8 kg/cm 2 ), pressure cycling switch will open and compressor clutch will disengage. As system equalizes and pressure cycling switch closes, compressor clutch will cycle on. This cycling continues and maintains evaporator discharge and temperature at approximately 33°F (1°C).
3. This step determines if signal is reaching ECM on circuit No. 66 from A/C control panel. Signal should only be present when A/C mode or defrost mode is selected.
4. With engine idling and A/C on, ECM should ground circuit No. 459, causing test light to illuminate.

If complaint is insufficient cooling, problem may be caused by inoperative cooling fan(s) or faulty A/C refrigerant fan request switch. Engine cooling fan(s) should turn on when A/C pressure exceeds a value to open switch, causing ECM to energize cooling fan relay(s). See CHART C-12 for cooling fan diagnosis. If fan operates correctly, ensure A/C system refrigerant charge is okay.

Scheme 92

Scheme 93

C-10, A/C CLUTCH CNTRL CKT DIAGNOSIS - 3.1L (REAR A/C ONLY)

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if signal is reaching ECM from A/C control panel. Signal should only be present when A/C mode or defrost mode is selected.

If complaint is insufficient cooling, problem may be caused by inoperative cooling fan(s) or A/C refrigerant fan request switch. Engine cooling fan(s) should turn on when A/C pressure exceeds a value to open switch, which causes ECM to energize cooling fan relay(s). See CHART C-12 for cooling fan diagnosis. If fan operates correctly, ensure A/C system refrigerant charge is okay.

Scheme 94

C-10, A/C CLUTCH CONTROL CIRCUIT DIAGNOSIS - 3.8L

PCM delays A/C compressor clutch engagement about .4 seconds after A/C is turned on. This delay allows Idle Air Control (IAC) motor to adjust engine RPM before compressor clutch engages. PCM also disengages A/C compressor clutch during Wide Open Throttle (WOT) operation. A/C compressor clutch is energized when PCM grounds circuit No. 459. PCM may engage A/C compressor clutch during engine cranking.

Note. Test numbers refer to numbers on diagnostic charts.

Scheme 95

Scheme 96

Scheme 97

Scheme 98

1. A/C compressor clutch should not be engaged with engine running if an A/C mode is not selected at control head.
2. A/C compressor clutch should apply if conditions under NOTICE at top of chart are met.
3. Checks for an A/C request signal from control head to pressure cycling switch.
4. Checks for ignition voltage on circuit No. 639 and PCM control of ground circuit No. 459 to A/C compressor clutch relay coil.
5. Checks for ignition voltage on circuit No. 639 to A/C compressor clutch relay contacts.
6. Determines if A/C compressor clutch relay, compressor clutch coil or circuitry is faulty.
7. Determines if PCM is turning on A/C compressor clutch relay due to a false A/C request signal.
8. Checks for circuit No. 59 shorted to B+ or a faulty A/C compressor clutch.
9. Isolates problem to A/C control head and circuits No. 66 and 257 to pressure cycling switch or circuit No. 67 and PCM.
10. Determines if A/C compressor clutch relay is faulty or A/C compressor clutch relay control circuit No. 459 is grounded at all times.

CHART C-10, A/C CONTROL DIAGNOSIS (A/T) 4.3L TURBO PFI

ECM controls operation of A/C clutch to improve idle quality and performance by

1. Delaying A/C clutch application until idle air rate is increased.
2. Releasing A/C clutch when idle speed is too low.
3. Releasing A/C clutch at wide open throttle operation.
4. Smooths cycling of compressor by providing additional fuel the instant A/C clutch is applied.

Turning on A/C supplies battery voltage to clutch relay (circuit No. 59) and ECM terminal BC9. After a time delay of .5 seconds, ECM grounds terminal GF1 (circuit No. 459), and closes control relay. A/C compressor clutch then engages.

Note. Test numbers refer to numbers on diagnostic charts.

1. Checks for low refrigerant as cause for no A/C.
2. This step and steps that follow check for faulty A/C control relay. See QUAD DRIVER CHECK under «COMPUTERIZED ENGINE CONTROLS»(ref-19439-S14016610752001010200000) .
3. Checks for faulty cycling switch. Solenoids and relays are turned on and off by ECM, using "drivers". Each driver is a part of a group of 4, called quad-drivers. Failure of one driver can damage any other driver in set. Solenoid and relay coil resistance should be greater than 20 ohms.

Scheme 99

Scheme 100

Check resistance of each ECM controlled relay or solenoid before replacing ECM. See CONTROL UNIT under COMPUTERIZED ENGINE CONTROLS. Replace any relay or solenoid that measures less than 20 ohms.

Scheme 101

CHART C-12, COOLING FAN CIRCUIT DIAGNOSIS 3.1L

ECM controls electric cooling fan(s) based on inputs from coolant temperature sensor, A/C request, refrigerant fan request switch and vehicle speed. ECM energizes fan(s) by grounding circuits No. 335 and No. 473, which closes cooling fan relay(s). Battery voltage is supplied to cooling fan(s) when energized by ECM. ECM grounds circuit No. 335 (puller fan) when coolant temperature is approximately 223°F (106°C) or when A/C has been requested and refrigerant fan request switch opens with high A/C pressure, approximately 200 psi (14.1 kg/cm 2 ). Pusher fan relay is grounded when coolant temperature is approximately 217°F (103°C) and/or puller fan is energized for A/C pressure.

Note. Test numbers refer to numbers on diagnostic charts.

1. With Data Link Connector (DLC) grounded, cooling fan driver closes and energizes fan control relay.
2. If A/C fan request switch or circuit is open, cooling fan operates whenever A/C is operating.
3. With A/C requested and 45 seconds after request is removed, A/C refrigerant fan request switch should open when A/C high pressure exceeds approximately 200 psi (14.1 kg/cm 2 ). This signal should cause ECM to energize fan control relays(s).
4. This test checks if cooling puller and pusher fan relay(s) (circuits No. 335 and 473) are shorted to ground. This condition would cause fans to be energized continuously.

If an overheating condition is suspected, verify if it is due to actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge/light circuit for malfunction.

If vehicle is overheating and gauge or light indicates so, but cooling fan is not operating and scan tester indicates normal readings, coolant temperature sensor is out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.

Scheme 102

Scheme 103

Note. Test numbers refer to numbers on diagnostic charts.

1. Battery voltage should be available at cooling fan relay terminals "A" and "D" when ignition switch is in ON position.
2. This checks ECM's ability to ground circuits No. 335 and 473. Malfunction Indicator Light (MIL) should be flashing at this point. If MIL is not flashing, refer to TESTS W/CODES article in this section.
3. This test checks if cooling puller and pusher fan relays (circuits No. 533 and 702) are open. Jumpering relay terminals "A" and "E" by-passes relay, which should cause fans to operate, if motors and wiring are okay.

Scheme 104

CHART C-12A, COOLING FAN CIRCUIT DIAGNOSIS 3.8L

Power for fan motor goes through a 40-amp fusible link to terminal "A" of fan relays. Fan relays are energized when a good ground circuit is completed through Powertrain Control Module (PCM) quad-driver. PCM energizes puller relay through terminal "GC4", when coolant temperature reaches 212°F (100°C) or when A/C is requested. PCM energizes pusher relay if A/C refrigerant pressure reaches 210 psi (99°C) or coolant temperature reaches 226°F (108°C).

Note. Test numbers refer to numbers on diagnostic charts.

1. Using Tech 1 miscellaneous tests, low speed fan control will cause PCM to ground circuit No. 335. Puller fan should operate.
2. Using Tech 1 miscellaneous tests, high speed fan allows control of circuit No. 473. Pusher fan should operate.
3. When jumpering coolant temperature sensor wires together, scan tester should display coolant temperature of 304°F (151°C). Both fans will operate when ignition is cycled from off to on.
4. Opening A/C pressure switch will cause pusher fan to operate.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check PCM harness connector for backed out terminals. Connect a DVOM between affected terminal and ground. Wiggle related wires and connectors while watching DVOM for voltage reading change. Ensure coolant temperature sensor is not scaled improperly. See Code 15 in appropriate TESTS W/CODES article in this section. Ensure engine cooling system is operating normally.

Scheme 105

Scheme 106

Note. Test numbers refer to numbers on diagnostic charts.

1. Checks if circuit No. 335 is shorted to ground, keeping relay closed at all times.
2. Checks if circuit No. 473 is shorted to ground. An illuminated test light, indicates wire is shorted to ground.
3. If test light is off after disconnecting PCM, ensure circuit No. 335 is not shorted to B+. If circuit is not shorted to B+, PCM is shorted internally.
4. If test light is off after disconnecting PCM, ensure circuit No. 473 is not shorted to B+. If circuit is not shorted to B+, PCM is shorted internally.

Scheme 107

Note. Test numbers refer to numbers on diagnostic charts.

1. Checks for battery voltage at relay harness connector.
2. Jumpering cooling fan relay terminals "A" and "E" by-passes relay, causing fans to operate, if fan motors and wiring are okay.
3. Grounding test terminals should cause PCM to ground circuit No. 335. At this point, test light should illuminate, if PCM is good and circuit No. 335 is not open.
4. Checks for battery voltage and ground to fan motor. Test light illuminated at this point indicates a faulty fan motor connection or motor.

Scheme 108

Note. Test numbers refer to numbers on diagnostic charts.

1. Test light should be illuminated because harness terminal "F" has battery voltage with ignition in ON position.
2. Jumpering relay harness terminals "A" and "E" by-passes relay. If fan runs, relay is faulty.
3. Checks circuit No. 473 back to PCM. If circuit No. 473 is okay, relay is bad.
4. Checks wiring to cooling fan motor. If wiring is okay, problem is in connections, motor or motor ground.

Scheme 109

Scheme 110