P0873
UniversalTransmission Fluid Pressure Sensor/Switch C Circuit High
Medium SeverityThis code indicates that the vehicle's powertrain control module (PCM) has detected an abnormally high voltage reading in the circuit for the Transmission Fluid Pressure Sensor/Switch C. This typically means the sensor is sending an incorrect high signal, which can disrupt proper transmission operation and lead to noticeable issues with gear shifting.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is safely supported on jack stands before working underneath. Allow the transmission to cool before handling fluid, as it can be very hot. Disconnect battery before performing any electrical work. Wear appropriate personal protective equipment, including gloves and eye protection, to avoid contact with hot fluids and sharp components.
Common Symptoms
- Check Engine Light illuminated
- Harsh or erratic gear shifting
- Transmission slipping
- Transmission may enter 'limp mode'
- Delayed engagement of gears
Common Causes
- Faulty Transmission Fluid Pressure Sensor/Switch C
- Wiring harness issues (e.g., chafed, broken, shorted to voltage, or corroded wires)
- Poor electrical connection at the sensor or Powertrain Control Module (PCM)
- Contaminated or incorrect transmission fluid
- Internal transmission mechanical failure (less common for a 'circuit high' fault, but possible)
- Faulty Powertrain Control Module (PCM) (rare)
Frequently reported on: General/Universal
Diagnostic Steps
- Verify the P0873 code with an OBD-II scanner and check for any other related transmission or engine codes.
- Inspect the wiring and connectors leading to the Transmission Fluid Pressure Sensor/Switch C for any signs of damage, corrosion, or loose connections. Repair as necessary.
- Check the transmission fluid level and condition; ensure it is at the proper level and not burnt, discolored, or contaminated. Top up or replace fluid if needed.
- If the sensor is accessible, use a multimeter to test the resistance or voltage of the sensor circuit according to your vehicle's service manual specifications.
- If wiring and fluid appear normal and the sensor tests faulty, replace the Transmission Fluid Pressure Sensor/Switch C. This often requires dropping the transmission pan and valve body access.
- Clear the code with the OBD-II scanner and test drive the vehicle to confirm the repair has resolved the issue.
👨🔧 When to Call a Professional
If, after initial diagnostics, the cause of the P0873 code is not readily apparent, or if transmission shifting issues worsen significantly, it is best to consult a professional mechanic. Continued driving with an improperly functioning transmission fluid pressure sensor could lead to more serious transmission damage over time.
Commonly Asked Questions
Can I drive with a P0873 code?
While your vehicle might still be drivable, it is not recommended to drive for extended periods with a P0873 code. The code indicates an issue with the transmission's ability to accurately monitor fluid pressure, which can lead to erratic shifting, 'limp mode,' and potentially cause more significant transmission damage if ignored.
Is replacing the transmission fluid pressure sensor C difficult?
The difficulty of replacing this sensor largely depends on its specific location. Many transmission fluid pressure sensors are located inside the transmission's valve body, requiring the transmission pan to be dropped and potentially the valve body removed, which can be an advanced DIY task.
What does 'Circuit High' mean in the context of this sensor?
A 'Circuit High' reading typically indicates that the voltage signal from the sensor to the Powertrain Control Module (PCM) is higher than the expected operating range. This could be caused by a faulty sensor, a short to voltage in the wiring, or, less commonly, an issue with the PCM itself.
Do I need to change my transmission fluid if I get this code?
Not necessarily as a primary fix, but it's crucial to check the transmission fluid level and condition. If the fluid is low, burnt, or excessively dirty, addressing these fluid issues should be done, as they can sometimes contribute to sensor problems. However, the sensor itself may still be faulty even with good fluid.
What tools are essential to diagnose a P0873 code?
An OBD-II scanner is essential to read and clear the diagnostic trouble code. A multimeter is very helpful for testing wiring continuity, resistance, and voltage signals from the sensor. You will also need basic hand tools, and potentially a new transmission pan gasket and fluid if accessing the sensor inside the transmission.