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HOMESERVICE MANUALSCHEVROLET1999SUBURBAN C2500, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P1537-U1193DTC P1652DTC P1652: FAN 2 RELAY CONTROL CIRCUIT (3.4L "N" BODY)DIAGNOSTIC PROCEDURES
1999 Chevrolet Suburban C2500, 6.5 F

Diagnostic Procedures

1999 Chevrolet Suburban C2500, 6.5 FSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
  2. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and high speed fan control circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step  7.
  3. Turn ignition off. Remove cooling fan No. 2 and 3 relays. Leave PCM harness connector disconnected. Using DVOM, check voltage between high speed fans control circuit and ground. If voltage reading is zero volts, go to next step. If voltage reading is not zero volts, go to step  6.
  4. Reinstall cooling fan No. 2 and 3 relays. Using DVOM, set DVOM to 10-amp range. Turn ignition on. Check current between ground and high speed fans control circuit. Monitor reading for about 2 minutes. If current is 0.1-1.5 amps, go to step  12. If current is not 0.1-1.5 amps, go to next step.
  5. Turn ignition off. Remove fan No. 3 relay connector. Turn ignition on. Using DVOM, set DVOM to 10-amp range. Check voltage between ground and fan 3 relay driver circuit. If current reading is 0.1-1.5 amps, go to step  15. If current reading is not 0.1-1.5 amps, go to step  16.
  6. Locate and repair short to voltage in high speed fans control circuit. After repairs, go to step  18.
  7. Check battery feed fuse to cooling fan relay No. 2 and 3. If fuse is blown, go to next step. If fuse is okay, go to step  9.
  8. Locate and repair short to ground in battery feed circuit for cooling fan No. 3 relay. Replace fuse. After repairs, go to step  18.
  9. Disconnect cooling fan No. 3 relay. Turn ignition on. Check voltage between ground and battery feed circuit terminal at cooling fan No. 3 relay harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step  14.
  10. Check for an open or short to ground in high speed fan control circuit. Repair as necessary. After repairs, go to step  18. If circuit is okay, go to step  15.
  11. Check output driver circuit and battery feed circuit for poor connection at cooling fan No. 3 relay and at PCM. Repair as necessary. After repairs, go to step  18. If circuits are okay, go to step  15.
  12. Turn ignition off. Reconnect PCM harness connector. Disconnect cooling fan No. 3 relay. Turn ignition on. Connect a test light between ground and cooling fan No. 3 relay control circuit terminal. Using scan tool, cycle cooling fan No. 3 relay on and off. If test light flashes on and off, see DIAGNOSTIC AIDS . If test light does not flash on and off, go to next step.
  13. Check high speed fans control circuit for poor connection at PCM. Repair as necessary. After repairs, go to step  18. If connections are okay, go to step  17.
  14. Locate and repair open on battery feed circuit to cooling fan No. 2 and 3 relays. Check for poor terminal connections between cooling fan No. 2 Maxi-Fuse® and fuse block. Repair as necessary. After repairs, go to step  18.
  15. Replace cooling fan No. 3 relay. After replacing relay, go to step  18.
  16. Replace cooling fan No. 2 relay. After replacing relay, go to step  18.
  17. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  18. Using scan tool, select CLEAR INFO or CLEAR DTCs function to clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for this DTC until DTC test runs. If scan tool indicates that this DTC FAILED THIS IGN, repeat step  2. If scan tool does not indicate that this DTC FAILED THIS IGN, repair is complete.
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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.