P0502 The vehicle speed sensor signal is lower than the computer expects

Vehicle speed sensor low input

P0502 in short

P0502 means the computer is getting a lower speed signal than expected from the vehicle speed sensor. Damaged wiring, a faulty sensor or reluctor ring, debris, and sometimes water in the sensor are listed causes. ABS may switch off, so get it checked soon.

The vehicle speed sensor feeds the computer the data it needs for shifting, cruise control and the speedometer. P0502 sets when that signal is lower than it should be.

TroubleCodes.net lists damaged or corroded wiring, a defective sensor or damaged reluctor ring, metal debris on the sensor, and rarely a failed module. It says ABS can be switched off automatically until the fault is fixed.

General Motors has bulletins naming P0502. One for 2013-2016 Cadillac ATS and 2014-2015 Corvette manual transmissions says P0502 can be caused by water in the transmission output speed sensor or by holding the car on a hill with the clutch slipping; another points to a transfer case control module that is not communicating on 2005-2009 medium-duty trucks.

Most likely causes

  1. Damaged wiring, connector or speed sensor

    Common general cause
    Why it ranks here
    TroubleCodes.net lists wiring, connectors and defective sensors including damaged reluctor rings.
    What would change this
    Rises if the connector is damaged or wet, or the signal drops while wiggling the harness. Falls if the signal is clean.

  2. Metal debris on the sensor

    Common general cause
    Why it ranks here
    TroubleCodes.net lists metal wear particles as interfering with the sensor.
    What would change this
    Rises if the sensor tip is coated with metal. Falls if it is clean.

  3. Water in the manual transmission output speed sensor (Cadillac ATS, Corvette)

    Supported by vehicle data
    Why it ranks here
    GM's bulletin PI1489A names water intrusion into the manual transmission output speed sensor, or prolonged clutch slipping on a hill, for P0502 with an intermittent no-Reverse condition.
    What would change this
    Rises on the listed cars if the reverse problem is intermittent. Falls on other vehicles.

  4. Transfer case control module not communicating (C4500-C5500 trucks)

    Supported by vehicle data
    Why it ranks here
    GM PIT-4865 says an inoperative speedometer with P0502 or P0500 on these trucks could be caused by the transfer case control module not communicating.
    What would change this
    Rises on the listed trucks if the module will not communicate with a scan tool. Falls on other vehicles.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes with a scan tool and check whether ABS, cruise or transmission codes are stored with P0502, and compare the scan tool's vehicle speed with the speedometer.

    Low riskTool: OBD-II scan tool

  2. Have a shop test the speed sensor wiring and sensor output as the wheels or output shaft turn, and check the sensor and reluctor ring for debris or damage.

    Best left to a shopTool: multimeter, scan tool

    Warning:The vehicle must be lifted for this; use jack stands. ABS and transmission parts are safety-related.

Symptoms

  • Speedometer or odometer not working or erratic
  • ABS or traction control light on Gets more serious: stop and have it checked.
  • Harsh or erratic shifting Gets more serious: stop and have it checked.
  • Intermittent inability to shift into Reverse on some manual cars

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

On your vehicle

Cadillac

  • 2013–2016 · ATS

    Supported by vehicle data

    GM bulletin links P0502 to water in the manual transmission output speed sensor and an intermittent no-Reverse condition.

  • PI1489 (cadillac)Status unverified

    MIL on, P0502 vehicle speed sensor circuit low voltage; may be unable to shift into Reverse

    2013–2016ats · issued · NHTSA 10113686

    Water in the manual transmission output speed sensor, or slipping the clutch on a hill, can set P0502.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chevrolet

  • PI1489 (chevrolet)Status unverified

    MIL on, P0502 vehicle speed sensor circuit low voltage

    2014–2015corvette · issued · NHTSA 10113686

    Same GM bulletin for Corvette; the NHTSA summary only identifies P0502 as VSS circuit low voltage.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIT-4865 (chevrolet)Status unverified

    Inoperative speedometer and/or SES light with P0502 or P0500

    2006–2009kodiak · issued · NHTSA 10030732

    The cause could be the transfer case control module not communicating on the Class 2 bus (C4500-C5500).

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0500Vehicle speed sensor signal missing or not believable

    Same system Supported by vehicle data

    P0500 is the general vehicle speed sensor malfunction code; GM lists it with P0502 for the same truck issue.

  • P0501The vehicle speed sensor signal is out of range or does not make sense

    Same system Common general cause

    P0501 is the range/performance code for the same sensor.

All Vehicle speed, idle control and engine electrical codes

Sources and review

  1. P0502 code definition and diagnosis — TroubleCodes.net
  2. GM PI1489: MIL on, DTC P0502 vehicle speed sensor circuit low voltage (2013-2015 Cadillac ATS, 2014-2015 Corvette) — General Motors / NHTSA ,
  3. GM PIT-4865: inoperative speedometer and/or SES MIL with P0502 or P0500 (2005-2009 Chevrolet Kodiak, GMC TopKick C4500-C5500) — General Motors / NHTSA ,
  4. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
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