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Home >> Cadillac >> 1996 >> Seville SLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1641 - Malfunction Indicator Light (Mil) Control Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. Turn ignition on. Check if MIL illuminates after 5 seconds. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 4).
  3. Using scan tool, enter OUTPUT TESTS then select MIL. Command MIL off. If MIL turns off, fault is not present. See DIAGNOSTIC AIDS. If MIL does not turn off, go to step 8).
  4. Select ENGINE 3 mode and note MALFUNCTION IND LAMP DRIVER display on scan tool. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6).
  5. Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Remove IP cluster fuse. Turn ignition on. Using DVOM, check voltage between ground and MIL signal circuit at PCM harness connector C2 terminal. If voltage reading is .5 volt or greater, go to step 9). If voltage reading is not .5 volt or more, go to step 13).
  6. Reinstall IP cluster fuse. Using a jumper wire, jumper MIL signal circuit at PCM harness connector C2 to ground. If MIL illuminates, go to step 13). If MIL does not illuminate, go to next step.
  7. Check condition of IP fuse. If fuse is faulty, go to step 10). If fuse is okay, go to step 13).
  8. Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. If MIL illuminates, go to step 12). If MIL does not illuminate, go to step 13).
  9. Repair short to voltage in MIL signal circuit.
  10. Repair short to ground in circuit between MIL and fuse block.
  11. Repair open in MIL circuit from fuse block to PCM. Check for faulty MIL bulb.
  12. Replace short to ground in MIL circuit between MIL bulb and PCM.
  13. Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal connector is okay, go to next step.
  14. Replace PCM. Program replacement PCM using required equipment.
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