Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1997CHEVY EXPRESS G3500, VAN CARGO EXTENDED, 5.7 RREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM & COMPONENT TESTS - 5.7L (G SERIES)MISCELLANEOUS PCM/VCM CONTROLSELECTRIC COOLING FAN CIRCUIT DIAGNOSIS (WITHOUT AUXILIARY FAN CONTROL SWITCH)COOLING FAN CIRCUIT DIAGNOSIS
1997 Chevrolet Chevy Express G3500, Van Cargo Extended, 5.7 R
Cooling Fan Circuit Diagnosis
1997 Chevrolet Chevy Express G3500, Van Cargo Extended, 5.7 RSECTION Cooling Fan Circuit Diagnosis
- If cooling fan does not operate, or does not operate properly, go to next step. If cooling fan runs continuously with ignition off, go to step 12). If cooling fan runs continuously with ignition on, go to step 13).
- If cooling fan motor never operates, go to next step. If cooling fan motor does not operate with high coolant temperature, go to step 9). If cooling fan motor does not operate with A/C on, go to step 10).
- Turn ignition off. Disconnect fan control relay harness connector. Turn ignition on. Using a test light connected to ground, probe fan control relay harness connector terminal No. 30. If test light comes on, go to next step. If test light does not come on, locate and repair open in Red wire between fan control relay and splice near fusible link.
- Using a fused jumper wire, jumper fan control relay harness connector terminals No. 30 and 87 together. If cooling fan motor runs, go to next step. If cooling fan motor does not run, go to step 6).
- Disconnect jumper wire. Using a test light connected to ground, probe fan control relay harness connector terminal No. 85. If test light comes on, go to step 8). If test light does not come on, locate and repair open in Pink wire between ENG 1 fuse and fan control relay.
- With jumper wire still in place, disconnect cooling fan motor harness connector. Using a test light connected to ground, probe cooling fan motor harness connector terminal "B". If test light comes on, go to next step. If test light does not come on, locate and repair open in Red wire between fan control relay and cooling fan motor.
- Using a test light connected to battery positive, probe cooling fan motor harness connector terminal "A". If test light comes on, replace cooling fan motor. If test light does not come on, locate and repair open in Black wire between cooling fan motor and ground.
- Reconnect fan control relay. Using a voltmeter, measure voltage (backprobe) between fan control relay harness connector terminal No. 86 and ground. If reading is less than 10 volts, replace fan control relay. If reading is 10 volts or greater, locate and repair open in Dark Green wire between fan control relay and splice.
- Disconnect auxiliary fan control switch harness connector. Turn ignition on. Using a voltmeter, measure voltage between auxiliary fan control switch harness connector terminal "A" and ground. If reading is less than 10 volts, locate and repair open in Dark Green wire between auxiliary fan control switch and splice. If reading is 10 volts or greater, replace auxiliary fan control switch.
- Disconnect A/C high pressure switch harness connector. Using a voltmeter, measure voltage between auxiliary fan control switch harness connector terminal "B" and ground. If reading is 10 volts or greater, go to next step. If reading is less than 10 volts, locate and repair open in Dark Green wire between A/C high pressure fan switch and splice.
- Using a test light connected to battery positive, probe A/C high pressure switch harness connector terminal "A". If test light comes on, replace A/C high pressure fan switch. If test light does not come on, locate and repair open in Black wire between A/C high pressure switch harness connector terminal "A" and splice.
- With ignition on, disconnect fan control relay harness connector. If cooling fan motor stops, replace fan control relay. If cooling fan motor continues to run, locate and repair short to power in Red wire between fan control relay and cooling fan motor.
- Turn ignition off. Disconnect fan control relay harness connector. Using a test light connected to battery positive, probe cooling fan relay harness connector terminal No. 86. If test light comes on, go to next step. If test light does not come on, replace fan control relay.
- With test light still connected, disconnect auxiliary fan control switch harness connector. If test light remains on, go to next step. If test light does not remain on, replace auxiliary fan control switch.
- With test light still connected, disconnect A/C high pressure fan switch harness connector. If test light remains on, locate and repair short to ground in Dark Green wire between fan control relay and either A/C high pressure fan switch or auxiliary fan control switch.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.