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Home >> Cadillac >> 1998 >> Eldorado Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1642 - Vehicle Speed Output Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.
  2. Turn ignition on, engine off. Using scan tool, select Vehicle Speed Output Signal display. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6).
  3. Start engine. Raise vehicle wheels off the ground. Using scan tool, check if wheels are generating a vehicle speed signal. If scan tool indicates OPEN/SHORT, go to next step. If scan tool does not indicate OPEN/SHORT, fault is not present. See DIAGNOSTIC AIDS.
  4. Using scan tool record fluid life index. Turn ignition off. Wait 30 seconds then disconnect PCM harness connector. Turn ignition on, engine off. Using DVOM, check voltage between ground and PCM harness connector terminal No. 25. If voltage reading is 10 volts or greater, go to step 7). If voltage reading is not 10 volts or greater, go to next step.
  5. Repair open or short to ground in vehicle speed output circuit. After repairs, perform PCM diagnosis. See POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  6. Repair short to voltage in vehicle speed output circuit. After repairs, perform PCM diagnosis. See POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  7. Check terminal contact at PCM. Repair as necessary. After repairs, perform PCM diagnosis. See POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. If terminal contact is okay, go to next step.
  8. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, perform PCM diagnosis. See POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
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