Vehicle Speed Circuit Check

DTC P1502 INSPECTION

DTC P1502		VEHICLE SPEED CIRCUIT CHECK
STEP	INSPECTION		ACTION
1	P1502: CHECK VEHICLE SPEED PID 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). Key ON. Connect NGS tester. 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 step 5.
1		No	Key OFF. The VSS PID value was not as expected. Go to step 2.
2	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. Key OFF. Was voltage(s) less than 1.0 volt?	Yes	Go to step 3.
2		No	Go to step 6.
3	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. Is each resistance less than 5.0 ohms?	Yes	Go to step 4.
3		No	Repair open circuit(s). Go to step 7 and complete VSC Repair Verification Drive Cycle.
4	CHECK VSC FOR SHORTS TO GROUND IN HARNESS Disconnect NGS tester from DLC. Measure resistance between ground and VSC SIG circuit at the PCM harness connector. e Is each resistance greater than 10,000 ohms?	Yes	Restore vehicle. See TROUBLE SHOOTING in REAR WHEEL ANTI-LOCK BRAKE SYSTEM article in Brakes or TROUBLE SHOOTING in FOUR WHEEL ANTI-LOCK BRAKE SYSTEM article in Brakes for further diagnosis of the ABS control module, its speed sensors and its wheel speed sensor harness circuits. If those components are working properly, replace the PCM. See POWERTRAIN CONTROL MODULE in REMOVAL, OVERHAUL & INSTALLATION article. . Go to step 7 and complete VSC Repair Verification Drive Cycle.
4		No	Go to step 6.
5	VISUAL INSPECTION Visually inspect the vehicle speed circuit harness circuits for any potential failure. 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. Did the visual inspection reveal any potential failure?	Yes	Repair fault as necessary. Go to step 7 and complete VSC Repair Verification Drive Cycle.
5		No	Unable to duplicate or identify fault at this time. Fault may be intermittent. See TROUBLE SHOOTING in REAR WHEEL ANTI-LOCK BRAKE SYSTEM article in Brakes or TROUBLE SHOOTING in FOUR WHEEL ANTI-LOCK BRAKE SYSTEM article in Brakes for further diagnosis of the ABS control module, its speed sensors and its wheel speed sensor harness circuits.
6	VERIFY IF VSC IS SHORTED IN HARNESS OR ANOTHER MODULE Determine which, if any, modules are connected to the VSC. (Refer to SYSTEM WIRING DIAGRAMS for B2500, SYSTEM WIRING DIAGRAMS for B3000, SYSTEM WIRING DIAGRAMS for B4000). If no other modules are connected to the VSC, go to the "YES" Action. 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 step 7 and complete VSC Repair Verification Drive Cycle.
6		No	See REAR WHEEL ANTI-LOCK BRAKE SYSTEM article in Brakes or FOUR WHEEL ANTI-LOCK BRAKES article in Brakes for further diagnosis of appropriate module. After repair, restore vehicle. Go to step 7 and complete VSC Repair Verification Drive Cycle.
7	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. See DIAGNOSTIC TROUBLE CODE NUMBERS .
7		No	Testing is complete. The repair has been verified.