P0725 is a common OBD2 code that can occur in the Volkswagen Passat. It indicates an issue with the engine speed sensor input circuit (which measures the engine speed at the input shaft and helps the PCM determine when and how hard to shift the transmission).
It’s a generic code, which means it has the same meaning for the Passat as it would any other vehicle. Exact repair steps will depend on your Volkswagen’s model year and transmission type.
P0725 Definition: Engine Speed Input (Sensor) – Circuit Malfunction
Engine Speed Input Sensor
The engine speed input sensor is responsible for relaying data to your Passat’s PCM on how fast the engine turns. It can be referred to as the transmission input speed sensor, input speed sensor, or engine speed input sensor.
On most transmissions, it screws into the case near the front of the input shaft. A relcutor wheel turns with the input shaft, and the engine input speed sensor uses an electromagnetic field to measure how fast it is turning.
Circuit Malfunction
Your Volkswagen Passat’s engine speed input circuit sends data that it receives from the input speed sensor back to the PCM in the form of a voltage value. It’ll compare this value to the engine RPM, output speed sensor, and throttle position.
When the voltage value is not theoretically correct when compared to the other sensors, P0725 is stored in the PCM’s memory.
Volkswagen Passat P0725 Symptoms
While P0725 is not typically a full breakdown risk, there will usually be very difficult to drive. Here are the most common symptoms your Passat may experience:
- Check engine light
- Speedometer and tachometer not working properly (or at all)
- Transmission not shifting properly
- Not all gears are available, and harsh shifts (limp mode)
Volkswagen Passat P0725 Causes + Diagnosis
Here are the most common causes of P0725 in the Volkswagen Passat:
Dirty or Low Transmission Fluid
Since P0725 is a transmission-related trouble code. The first thing you should do is check the transmission fluid color. If it’s brown, black, or gray, there could be a transmission problem.
If there are metal flakes in the transmission, it can cause the input speed sensor to stop picking up the reluctor wheel.
Speed Input Sensor Wiring Issue
After confirming that your Passat’s transmission fluid is in good shape and properly filled, the next easiest thing to check is the wiring harness coming from the input speed sensor.
Check the harness for cracks or damage. If it appears damaged, replacing it may clear P0725.
Inspect the pins where it plugs into the speed input sensor. If the pins are damaged or corroded, you’ll either need to clean/replace them or repair the harness.
Bad Input Speed Sensor
A bad input speed sensor is the most common cause of P0725. Before replacing it, inspect it to see if there are any metal shavings on the magnetic tip.
Other Causes
Here are some other causes of P0725:
- Transmission Failure: If your Volkswagen Passat has a transmission that is slipping, it can create metallic debris that affects the input speed sensor.
- Bad PCM: This rarely happens but has been known to cause P0725.
- Failing Shift Solenoid(s): You’ll likely see metal debris on the dipstick if this were the case.
Conclusion
While a bad input speed sensor is perhaps the most common cause of P0725 in the Volkswagen Passat, it’s one of many potential causes. Good luck fixing your vehicle.