P0500 Code: Vehicle Speed Sensor A Malfunction

What the P0500 code means

The vehicle speed signal does not just move the speedometer needle. The engine computer uses it for idle strategy, the transmission uses it to decide when to shift, cruise control uses it to hold your speed, variable assist power steering uses it to adjust how heavy the wheel feels, and the audio system uses it to adjust the volume as you go faster.

That signal can come from a dedicated sensor at the transmission output or be calculated from the ABS wheel speed sensors, depending on the vehicle. On modern systems it usually travels over the data bus instead of a dedicated wire.

The P0500 code is stored when that signal is missing or does not agree with what the engine is doing. The computer sees engine rpm, load and a gear engaged, but no speed, or a speed that is impossible.

That is why the symptoms seem out of proportion for a single sensor: it is not one system that fails, several fail at once, and that confuses anyone who does not know how many functions depend on this one piece of data.

Here is a quick tip to point you in the right direction: check whether the odometer is still adding miles. On many vehicles the odometer uses the same signal as the speedometer, so if the odometer does not move either, the signal is not reaching the instrument cluster at all. If it moves normally but the engine computer stores the code, the signal exists and the problem is in the path to that module.

P0500 code symptoms

• Speedometer stuck at zero, erratic or giving readings that make no sense.
• Check engine light on, with the P0500 code stored.
• Harsh, late or missing shifts on automatic transmissions.
• Cruise control disabled.
• Power steering that does not change its effort with speed.
• Unstable idle when you come to a stop.
• Odometer that does not advance on some vehicles.
• Possible limp mode.
• The odometer stops adding miles along with the speedometer failure.

Likely causes of the P0500 code

1. Failed transmission speed sensor. The most frequent cause on vehicles that have one.
2. Cut or rubbed wiring along the path to the transmission.
3. Corroded or wet connector.
4. Worn drive gear on the sensor, or one with broken teeth.
5. Failed wheel speed sensor on systems that take the data from the ABS.
6. ABS module fault that stops it from sending the signal over the bus.
7. Blown fuse in the circuit.
8. Tires of a different size than the original, which throw off the calculation on some systems.
9. Poor ground in the circuit.

How to diagnose the P0500 code step by step

1. Check whether ABS codes are also stored. If they are, the speed data comes from that system and the cause is there.
2. Watch vehicle speed in live data while you drive slowly. It should rise smoothly and agree with the speedometer.
3. Compare the engine computer reading with the dashboard. A mismatch means the problem sits between the two.
4. Locate the sensor, normally at the transmission output, and inspect its connector and wiring.
5. Measure the sensor resistance if it is an inductive type, or check its supply voltage if it is a Hall effect type.
6. Lift the vehicle and spin the drive wheels while you watch the signal on the scan tool.
7. Inspect the drive gear when you remove the sensor, looking for damaged teeth.
8. Check the fuse and the ground of the circuit.
9. Check whether the odometer still adds miles. If it does not, the signal is not reaching the dashboard. If it does, the signal exists and the problem is in the path to the engine computer.

How to fix the P0500 code

• Replace the speed sensor if its measurements are out of range or it makes no signal when the wheels turn.
• Repair damaged wiring following its original routing and protect it from heat and rubbing.
• Clean or replace the corroded connector and apply dielectric grease.
• Replace the drive gear if it has damaged teeth, because a new sensor alone will not fix anything.
• Repair the ABS system if the data comes from it and there are codes in that module.
• Replace the fuse and find out why it blew.
• Fit tires of the original size if they were swapped for a different diameter.
• Aim the diagnosis at the sensor and its wiring if the odometer does not move either, and at the bus or the receiving module if the dashboard works normally.

Technical reference data

• Inductive sensors: typical resistance of 200 to 2000 ohms depending on the manufacturer.
• Hall effect sensors: 5 or 12 volt supply and a square wave signal whose frequency rises with speed.
• The signal can come from a dedicated sensor in the transmission or be calculated from the ABS wheel speed sensors.
• On modern systems it travels over the data bus and not on a dedicated wire.
• A change in tire size throws off the calculation on some vehicles.
• On many vehicles the odometer uses the same signal as the speedometer, so how it behaves tells you whether the signal reaches the dashboard.

Brand-specific notes

Before you go looking for a dedicated speed sensor, check whether your vehicle has one. On many recent models that part does not exist: the speed is calculated from the ABS wheel speed sensors and travels over the data bus, so the diagnosis points at that system and not at the transmission.

The quickest clue is the set of symptoms. If the ABS and the stability control fail along with the speedometer, the cause is in that module. If only the speedometer and the transmission fail, it points to a dedicated sensor.

Frequently asked questions about P0500