P0500 Vehicle Speed Sensor Malfunction

What does the P0500 OBD2 code mean?

The P0500 code, which stands for “Vehicle Speed Sensor Malfunction,” indicates there is an issue with the vehicle speed sensor (VSS) circuit. 

Specifically, it means:

• The powertrain control module (PCM) has detected inaccurate speed readings or a lack of signal from the VSS
• The PCM is not getting proper vehicle speed information from the VSS

The vehicle speed information is used for important systems like the speedometer, automatic transmission shifting, ABS, traction control, cruise control and more.

When P0500 is set, it means there is likely a fault in the VSS itself, the wiring to the VSS, or a PCM issue. 

Proper diagnosis is needed to pinpoint the exact cause and repair the problem. Ignoring the P0500 code risks driving with an inaccurate speedometer and compromised safety systems.

What Causes the P0500 Code?

There are a few common reasons that make the P0500 code triggers:

• Faulty Vehicle Speed Sensor (VSS): The VSS itself may be damaged or worn out. These sensors can fail over time due to normal wear and tear.
• Damaged Sensor Wiring: The wiring to the VSS may be damaged, causing an open or short circuit. This prevents proper signals from reaching the PCM.
• Issues with PCM: If the PCM has any internal faults, it may not be able to properly interpret signals from the VSS.
• Damaged Drive Gear: Some VSS designs use a drive gear that meshes with the speedometer gear on the transmission output shaft. If this plastic gear is damaged, the VSS cannot turn.
• Tire Size Mismatch: Using a different tire size than what the PCM is programmed for can cause speed calculation errors.

Proper diagnosis is important to pinpoint the exact cause in your vehicle.

Symptoms of a Bad Vehicle Speed Sensor

A failing VSS can produce various symptoms:

• Check Engine Light: The P0500 code will illuminate the Check Engine light on your dashboard.
• Speedometer/Odometer Problems: With inaccurate speed data, your speedometer may fluctuate erratically or stop working completely. Your odometer may also stop accumulating mileage.
• Automatic Transmission Issues: The PCM uses vehicle speed data to determine shift points. Incorrect data can lead to improper shifting.
• Traction Control Problems: Vehicle speed information is used by your traction and stability control system. Faulty data can disable these systems or cause them to activate erratically.
• ABS Malfunction: Your anti-lock brake system relies on individual wheel speed sensors. Bad data from the primary VSS can lead to ABS problems.

If you notice any of these symptoms, have the VSS inspected promptly. Continuing to operate your vehicle with a malfunctioning VSS can lead to dangerous situations.

How to Diagnose P0500 code

Diagnosing the cause of P0500 involves both electrical testing and physical inspection of components:

1. Retrieve Codes and Data

Connect a scan tool and read any diagnostic trouble codes stored in addition to P0500. 

Check freeze frame data for clues that may point to the cause.

2. Test Sensor Operation

With the scan tool, monitor the VSS signal while driving the vehicle. An oscillating signal that increases/decreases smoothly with road speed indicates proper sensor function.

3. Check VSS Voltage

Using a multimeter, back probe the VSS connector and check for a smooth AC voltage signal present between the signal and ground circuits. No voltage indicates open wiring, while abnormal voltages can point to sensor issues.

4. Inspect VSS Condition

Visually inspect the condition of the VSS, checking for damage or excessive wear. Rotate the gear/rotor and check for smooth spinning and proper resistance.

5. Check Wiring

Inspect wiring and connectors leading to the sensor for any chafing, breaks, or corrosion. Wiggle wiring while monitoring scanner data to check for shorts.

These steps will help isolate the issue and lead you towards the proper repair.

How to Fix P0500:

The exact repair needed depends on the cause determined during diagnosis:

• Replace Faulty Sensor: If the VSS is damaged internally or worn out, replacement of the complete sensor assembly will be required.
• Repair Wiring: Any corroded, loose, or broken wiring to the sensor must be repaired. Splicing in a new wire segment may be necessary.
• Replace PCM: If all other components check out okay, the PCM may need to be replaced and reprogrammed. This should be confirmed with further testing.
• Replace Drive Gear: On specific vehicle designs, damaged plastic gear will require sensor replacement along with the gear assembly.
• Correct Tire Size: Switch back to the OEM tire size or have the PCM reprogrammed for the new tire diameter.

The most cost-effective solution is often replacing the entire VSS assembly rather than just the internal sensor element. Proper repair will turn off the Check Engine light and restore proper vehicle operation.

Safety Precautions while fixing at home

Diagnosing and repairing the P0500 code at home involves some safety risks you need to be aware of:

• Use jack stands – Don’t just rely on a jack when working under the vehicle. Ensure it is safely supported on jack stands.
• Disconnect battery – Disconnect the negative battery terminal before doing any electrical testing or repairs to avoid shorts.
• Avoid hot exhaust – The engine and exhaust system will be hot after driving. Allow time for cooling or wear insulated gloves when working nearby.
• Protect eyes – Wear safety glasses when poking around the engine bay to prevent debris, dirt, or fluids from entering your eyes.
• Use fuses – When testing circuits with a multimeter, connect the meter leads through fuses to protect it from damage if contacting power accidentally.
• Torque properly – Follow spec torque values when reinstalling sensors or electrical connectors. Don’t over-tighten.
• Parts clean – Ensure electrical connectors are clean before reconnecting. Use electrical cleaner spray if dirty or corroded.
• Safety first – Don’t take unnecessary risks if you are uncertain about testing procedures or repairs. Ask for professional support instead.

Exercising caution and following proper safety practices will help prevent injury and damage while working on resolving your P0500 code at home.

Is it Safe to Drive With P0500?

Driving with a faulty VSS is not recommended due to the following safety concerns:

• Inaccurate speedometer readings prevent you from knowing your true road speed. This could lead to unsafe speeds or dangerous situations.
• Erratic automatic transmission shifting behaviour can significantly affect vehicle control.
• Disabled or inaccurate ABS and stability/traction systems severely reduce your vehicle’s ability to stop safely and maintain control in emergency situations.

While the car may seem to drive fine under normal conditions, the risks outlined above are too great to ignore. Schedule VSS repair as soon as possible.