P0871
UniversalTransmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
Medium SeverityThis code indicates a problem with the transmission fluid pressure sensor/switch C circuit, meaning the Powertrain Control Module (PCM) is receiving implausible signals regarding transmission fluid pressure. This can lead to issues with gear shifting and potentially put the transmission into a failsafe mode, affecting driveability.
⚠️ Before You Begin (Safety First)
Always allow the engine and transmission to cool before working on it. Disconnect the battery before performing any electrical repairs to prevent accidental shorts or damage. Be cautious of hot transmission fluid and moving parts.
Common Symptoms
- Check Engine Light (MIL) illuminated
- Harsh or erratic shifting
- Transmission slipping
- Transmission stuck in a single gear (limp mode)
- Delayed engagement of gears
- Reduced fuel economy
Common Causes
- Faulty Transmission Fluid Pressure Sensor/Switch C
- Wiring harness open or shorted in the sensor circuit
- Poor electrical connection at the sensor or PCM
- Contaminated transmission fluid
- Low transmission fluid level
- Internal transmission mechanical issues
- Faulty Powertrain Control Module (PCM) (rare)
Frequently reported on: General/Universal
Diagnostic Steps
- Check transmission fluid level and condition. Top up or replace if necessary.
- Visually inspect wiring and connectors for the transmission fluid pressure sensor (often located on or inside the transmission case). Look for damage, corrosion, or loose connections.
- Use an OBD-II scanner to clear the code and test drive to see if it returns.
- If accessible, use a multimeter to test the resistance and voltage of the transmission fluid pressure sensor circuit according to vehicle-specific repair manual specifications.
- If testing confirms sensor failure and it's externally mounted, replace the transmission fluid pressure sensor.
👨🔧 When to Call a Professional
If you lack experience with transmission diagnostics or if initial checks of wiring and external components do not resolve the issue, it's best to consult a professional transmission specialist to prevent further damage.
Commonly Asked Questions
Can I drive with a P0871 code?
It's not recommended to drive for extended periods as it can lead to transmission damage or unpredictable shifting. Address the issue as soon as possible.
What is the 'Transmission Fluid Pressure Sensor C'?
It's a sensor that monitors the hydraulic pressure in a specific circuit (C) within the transmission. This pressure is vital for proper gear engagement and smooth operation.
Is this an expensive repair?
The cost can vary significantly. If it's just a faulty external sensor or wiring, it might be moderate. If the sensor is internal or if there's a deeper underlying transmission issue, the cost could be substantial.
How do I locate the 'C' sensor?
Its exact location varies by vehicle, but it's typically either on the outside of the transmission case or inside the valve body. Consulting your vehicle's specific service manual is highly recommended.
Can low transmission fluid cause P0871?
Yes, low fluid levels or contaminated fluid can directly affect pressure readings within the transmission and potentially trigger this code, among others.