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2005 GMC Sierra 1500HD P050- Vehicle Speed Sensor A Low Input - Diagnosis and Fix

Model: 2005 GMC Sierra 1500HD Fault Code: P0502 Posted: 2017-08-29 13:27

My 2005 GMC Sierra 1500HD 6.0L 4WD crew cab truck suddenly started exhibiting strange shifting behavior one morning while pulling out of the driveway. Shortly after, the ABS light, brake warning light, and check engine light all illuminated. After returning home, I connected a OBD2 scanner and found fault code P0502: Vehicle Speed Sensor A - Low Input. I replaced all three vehicle speed sensors and their associated connectors, but the issue persists. During testing with a multimeter, I observed that the two sensors on the driver's side showed no signal, while the passenger-side sensor (identified as VSS #5) registered 1.1 volts when the key was turned on. The truck still exhibits erratic shifting and the P0502 code remains active. I'm seeking advice—what could be causing this? Is it a wiring issue, faulty sensor, or something else related to the vehicle speed sensing system?

Related fault codes
P0502
Comments (5)
Anonymous 2017-08-29 14:08

The Vehicle Speed Sensor (VSS) is typically located on the passenger side of the transmission. Please refer to your vehicle's wiring diagram to confirm sensor placement and connections.

Anonymous 2017-08-29 21:45

Thanks for the clarification, Kev2. I replaced all three VSS sensors and their wire connectors. As you mentioned, Sensor A is on the left side of the transmission. When I tested with a multimeter, the two driver-side sensors showed no voltage reading, while the passenger-side sensor (right side) registered 11.0 volts.

Anonymous 2017-08-30 03:21

P0502 points to Vehicle Speed Sensor A—this is typically VSS #5 in the wiring diagram. The sensor generates an AC voltage proportional to engine RPM, not a steady DC signal. Please confirm which sensor you tested on the right side (e.g., #4 or #6) and verify your reference diagram. I’ll follow up later if time permits.

Anonymous 2017-08-30 07:03

I tested VSS #4 on the right side—readings showed 11 volts, while VSS #6 on the same side showed no voltage at all.

Anonymous 2017-08-30 08:23

Focus your troubleshooting on VSS #5 (the passenger-side sensor) as it is directly associated with P0502. Remember that this sensor produces an AC signal proportional to vehicle speed, not a steady DC voltage. Since no other sensors show fault codes, the issue likely lies in the wiring or grounding of Sensor A—verify connections and ensure proper signal integrity.