Vehicle Speed Signal, Checking

General Description

The Vehicle Speed Signal or VSS measures Transmission / Transaxle output or Wheel Speed from the ABS System. The signal is broadcasted over the CAN Bus. The Engine Control Module -J623- uses this information to modify engine functions such as ignition timing, A/F ratio, transmission shift points, and to initiate diagnostic routines.

Special tools and workshop equipment required

Multimeter.
Wiring Diagram.
Scan Tool.

Test requirements

Fuses OK.
Battery voltage OK.
Switch OFF All electrical and electronic accessories.
Vehicles with Auto. Transmission, ensure Selector Lever position is in "P".
Vehicles with Manual Transmission, ensure Shifter Lever position is in "N" with Parking Brake applied.
Observe all safety precautions: SAFETY PRECAUTIONS .
View clean working conditions: CLEAN WORKING CONDITIONS .

Test Procedure

Step	Procedure	Result / Action to Take
1	PERFORM: Preliminary Check to verify the customers complaint. Refer to PRELIMINARY CHECK . -- Was Complaint verified?	-- YES: GO TO: Step 2 VEHICLE SPEED SIGNAL, CHECKING - 2 . -- NO: GATHER more information from customer about the complaint.
2	CONNECT: Scan Tool. ROAD TEST: Vehicle. CHECK: Scan Tool to Speedometer for accuracy. SPECIFIED VALUE: Difference ≤ 10%. -- Was Value obtained?	-- YES: CONDITION: May be intermittent. PERFORM: Visual Inspection of wiring and component. CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. REPAIR: Faulty wiring or connector. GO TO: Step 4 VEHICLE SPEED SIGNAL, CHECKING - 4 . -- NO: GO TO: Step 3 VEHICLE SPEED SIGNAL, CHECKING - 3 .
3	CHECK: ABS system. CHECK: ABS DTC's. -- Was the ABS system OK?	-- YES: CHECK: CAN Bus wiring from Instrument Cluster Control Module -J285- to ABS Control Module -J104-. GO TO: Step 4 VEHICLE SPEED SIGNAL, CHECKING - 4 . -- NO: REPAIR: Any ABS concerns 1st. GO TO: Step 4 VEHICLE SPEED SIGNAL, CHECKING - 4 .
4	Final Procedure Perform a road test to verify repair. -- Does the original DTC return?	-- YES: CHECK: Engine Control Module -J623- harness connector for any damaged, pushed-out pins. REPAIR: As necessary. If all electrical connections are OK: REPLACE: Engine Control Module -J623-. Refer to appropriate repair information. Clear the DTC's. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY . Repair is complete. Generate Readiness Code. Refer to READINESS CODE . Return vehicle to Customer. -- NO: Perform the diagnostic procedure for any DTC's. If no DTC's return the repair is complete. Return vehicle to customer.

DFD 07.21.2016