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Home >> Saab >> 2001 >> 9-5 Base, 4D Wagon, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Fault Code Diagnosis >> P0502: Vehicle Speed - No Input Signal >> Fault Isolation Procedure

Fault Isolation Procedure

  1. Checking DTCs in the ABS:
    • Turn the ignition switch to the ON position.
    • Contact ABS.
    • Obtain readouts of DTCs in the ABS.
    If DTCs C1371 or C1372 have been registered, see the appropriate ABS article under BRAKES, otherwise go to next step.
  2. Checking the wheel speed signal:
    • Jack up the front of the car.
    • Unplug the connector:
      • 4-Cyl: ECM control module (589).
      • V6: ECM control module (608).
    • Rotate the front left wheel.
    • Connect Test Lamp (86 1 857) to pins 23 and 64 of the female connector.
    • Jiggle the leads and in-line connectors at several places and in different directions to reveal intermittent breaks and short circuits in the wiring harness. Observe the multimeter, test lamp or diagnostic tool while doing this.
    If the test lamp flashes, go to step  4, otherwise go to next step.
  3. Checking the lead: Check to see if the lead from the ABS control module pin 25 to the ECM control module pin 64 is faulty. If there is a fault, rectify it and go to step  6, otherwise go to step  5.
  4. Checking the lead:
    • Stop the wheel in such a way that the lamp shines constantly.
    • Jiggle the leads and in-line connectors at several places and in different directions to reveal intermittent breaks and short circuits in the wiring harness. Observe the multimeter, test lamp or diagnostic tool while doing this.
    If the function is correct, go to step  6, otherwise go to step  3.
  5. Changing components: Change Control module, ABS. When finished, go to next step.
  6. Checking the vehicle speed signal:
    • Turn the ignition switch to the ON position.
    • Clear the DTCs in all systems.
    • Contact ECM.
    • Read value: Vehicle Speed (Wire from ABS) ECM.
    • Drive the car and check that the reading roughly corresponds to the reading on the speedometer.
    If the trouble code has recurred, the ECM is probably at fault and will need replacement. Replace with known-good ECM and retest. if no DTCs are present, then the steps taken to rectify the fault were correct.
Fig 1: ABS Control Module Circuit (4-Cyl)
G00207365Courtesy of SAAB-SCANIA OF AMERICA, INC.
Fig 2: TC/ABS & ESP Control Module Circuit (4-Cyl)
G00207366Courtesy of SAAB-SCANIA OF AMERICA, INC.
Fig 3: TC/ABS Control Module (V6)
G00207420Courtesy of SAAB-SCANIA OF AMERICA, INC.
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