P0842
UniversalTransmission Fluid Pressure Sensor/Switch A Circuit Low
Medium SeverityThe P0842 code indicates that the Powertrain Control Module (PCM) has detected a low voltage signal from the Transmission Fluid Pressure Sensor/Switch A circuit. This typically means the sensor is sending an abnormally low reading or there's an electrical issue in its circuit, leading to potential transmission shifting problems or the vehicle entering limp mode.
⚠️ Before You Begin (Safety First)
Always exercise caution when working around hot engine and transmission components. Allow the vehicle to cool down before inspection or repair. Disconnect the battery's negative terminal before performing any electrical work to prevent accidental shorts or injury. Use appropriate jack stands and never rely solely on a jack when working under the vehicle. Transmission fluid can be hot and cause burns.
Common Symptoms
- Check Engine Light illuminated
- Harsh or erratic transmission shifts
- Delayed engagement of gears
- Vehicle stuck in 'limp mode' (limited gears or speed)
- Loss of speedometer or odometer function (less common)
Common Causes
- Faulty Transmission Fluid Pressure Sensor/Switch A
- Open or short circuit in the sensor's wiring harness
- Poor electrical connection at the sensor or PCM
- Low transmission fluid level or contaminated fluid
- Internal transmission mechanical failure (less common, but possible)
- Failing Transmission Control Module (TCM)
Frequently reported on: General Motors (e.g., Chevrolet Silverado/Tahoe 2007-2013), Ford F-Series (e.g., F-150 2004-2008), Honda/Acura (various models 2005-2012), Nissan (various models 2007-2014)
Diagnostic Steps
- Check transmission fluid level and condition. Top off or replace if necessary.
2. Visually inspect the wiring harness and connectors for the Transmission Fluid Pressure Sensor/Switch A for damage, corrosion, or loose connections.
3. Using a multimeter, test the continuity and resistance of the sensor and its circuit. Refer to your vehicle's service manual for specific values.
4. If the sensor tests faulty, replace it. Be prepared for some transmission fluid loss during removal and replacement.
5. Clear the code with an OBD-II scanner and test drive the vehicle to verify the repair.
👨🔧 When to Call a Professional
While a faulty sensor is a common cause, don't overlook wiring harness issues or a failing Transmission Control Module (TCM). Always perform thorough diagnostic checks to rule out these possibilities. If multiple transmission-related trouble codes are present, or if the problem persists after replacing the sensor and inspecting wiring, it's advisable to consult a professional transmission specialist.
Commonly Asked Questions
What specifically does 'Circuit Low' mean for P0842?
'Circuit Low' means the Powertrain Control Module (PCM) is receiving a voltage signal from the Transmission Fluid Pressure Sensor/Switch A that is lower than expected, or even no signal at all, indicating a potential open circuit, short to ground, or a faulty sensor sending an incorrect low reading.
Can I continue driving my car with a P0842 code?
It is not recommended to drive for an extended period with a P0842 code. The transmission may not shift correctly, which can lead to accelerated wear, further damage to the transmission, or even put you in a dangerous situation if the vehicle suddenly loses power or shifts erratically.
Is replacing the Transmission Fluid Pressure Sensor/Switch A difficult?
The difficulty level is generally 'Medium'. It requires accessing the transmission, which may involve getting under the vehicle, and potentially dealing with transmission fluid. The sensor's location varies by vehicle, and some may be on the valve body inside the transmission, requiring the pan to be dropped.
Could a P0842 code be caused by low transmission fluid?
Yes, low transmission fluid can indirectly cause issues that trigger a P0842 code, as insufficient fluid can lead to incorrect pressure readings. Always check your transmission fluid level and condition as a first diagnostic step.
What is the difference between a transmission fluid pressure 'sensor' and a 'switch'?
A 'sensor' typically provides a continuous, variable voltage signal to the PCM that correlates to fluid pressure. A 'switch' usually provides an on/off signal when a specific pressure threshold is met. Many vehicles use sensors, but the code definition includes 'switch' for broader applicability.