Powertrain control module (PCM) detected an error in the vehicle speed information received from the anti-lock brake system (ABS) control module, generic electronic module (GEM) or central timer module (CTM).
Note: When diagnosing the VSC signal to the PCM refer to the chart below to determine which module sends the VSC signal to the PCM.
Key on.
Connect scan tool.
Access VSS PID.
Obeying all local traffic laws, complete the following:
Take the vehicle to a suitable location and gradually increase the vehicle speed to 80 km/h (50 mph), while observing the VSS PID mph values.
Did the VSS PID value match the speed at which you were traveling? Yes
KEY OFF. The VSS PID value was as expected. The fault that produced
DTC is intermittent. GO to DF5
.
No
KEY OFF. The VSS PID value was not as expected. GO to DF2
.
DF2 CHECK VSC FOR SHORT TO POWER IN HARNESS
Disconnect PCM.
Disconnect appropriate control module (ABS, GEM, or CTM).
Key on.
Measure voltage between VSC SIG circuit at PCM harness connector and ground.
For Excursion and F-Series:
Also measure voltage between VSC GND circuit at PCM harness connector and ground.
Key off.
Was voltage(s) less than 1.0 volt? Yes
GO to DF3
.
No
GO to DF6
.
DF3 CHECK FOR OPEN VSC BETWEEN PCM AND CTM, GEM, OR ABS CONTROL MODULE
Measure resistance of VSC circuit between PCM harness connector pin and the appropriate control module connector.
For Excursion and F-Series:
Also measure resistance of VSC GND circuit between PCM harness connector pin and ground.
Visually inspect the vehicle speed circuit harness circuits for any potential failures. Use the following check list for reference:
Loose harness connection of vehicle speed circuits at the appropriate control module.
Loose harness connection of vehicle speed circuits at the PCM.
Incorrect harness routing of vehicle speed circuits.
Note: Refer to Wiring Diagrams for harness, module and connector location. Did the visual inspection reveal any potential failure? Yes
REPAIR fault as necessary. GO to DF7
and COMPLETE
VSC Repair Verification Drive Cycle.
No
Unable to duplicate or identify fault at this time. REFER to
Antilock Brakes / Traction Control Systems, for diagnosis of
intermittent control module and wheel speed sensor concern.
DF6 VERIFY IF VSC IS SHORTED IN HARNESS OR ANOTHER MODULE
Determine which, if any, modules are connected to the VSC (Refer to Wiring Diagrams). If no other modules are connected to the VSC, GO to the "YES" Action To Take.
One at a time, disconnect the modules associated with the VSC. After disconnecting each module, again test for short circuit (Refer to test step that sent you here). Repeat until each associated module has been disconnected or the short circuit has been eliminated.
Did the short circuit remain after all associated modules were disconnected? Yes
REPAIR short circuit. GO to DF7
and COMPLETE VSC
Repair Verification Drive Cycle.
No
REFER to the diagnostic/repair information for further diagnosis of appropriate
module. After repair, RESTORE vehicle. GO to DF7
and COMPLETE
VSC Repair Verification Drive Cycle.
DF7 VSC REPAIR VERIFICATION DRIVE CYCLE
Warm engine to operating temperature. Complete the VSC Repair Verification Drive Cycle at least three times as described below: AUTOMATIC TRANSMISSIONS:
Place transmission range selector lever in DRIVE range.
Obey all local traffic laws.
Accelerate heavily to 56 km/h (35 mph).
Coast down to an idle and stop the vehicle.
Shut the engine off.
After the drive cycle is completed, retrieve any Continuous Memory DTCs.
MANUAL TRANSMISSIONS:
Shift to second from first gear.
Obey all local traffic laws.
Accelerate moderately to 64 km/h (40 mph).
Coast down to an idle and stop the vehicle.
After the drive cycle is completed, retrieve any Continuous Memory DTCs.
Were any Continuous Memory DTCs generated during the drive cycle? Yes
Testing is not complete. The repair has not been verified. REPAIR
