Transmission Fluid Pressure Sensor/Switch Circuit Low
The P0842 code indicates that the Powertrain Control Module (PCM) has detected a low voltage signal from the transmission fluid pressure (TFP) sensor or switch circuit. This sensor monitors hydraulic pressure inside the transmission to control shift timing and line pressure. A low circuit condition typically means the signal voltage is below the expected range (often below 0.5V), which can be caused by a faulty sensor, wiring issues, or low transmission fluid level. This can lead to harsh shifts, slipping, or limp mode.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifts
- Transmission slipping or overheating
- Vehicle enters limp mode
2. Most Common Causes
- Faulty transmission fluid pressure sensor
- Open or shorted wiring in the sensor circuit
- Low or contaminated transmission fluid
- Internal transmission mechanical failure
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Inspect transmission fluid level and condition; top off or replace if necessary.
Step 3: Visually check wiring and connector for damage, corrosion, or loose pins.
Step 4: Test sensor resistance and voltage with a multimeter; compare to specs.
Step 5: If sensor and wiring are good, suspect internal transmission issue or PCM fault.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as low transmission fluid pressure can cause internal damage. If the vehicle is shifting poorly or in limp mode, have it towed to a shop.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and sensor replacement. If wiring repair is needed, it may be slightly more. Internal transmission repairs can cost significantly more.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.