P0873

What it means

P0873 means the transmission control module has detected a high voltage or signal on the circuit for transmission fluid pressure sensor or switch 'C'. The signal sits above the expected range for the current gear, selector position or operating conditions. Which pressure sensor or switch is 'C', and where it sits, depends on the vehicle and transmission, so check the manufacturer's information for the exact model.

Symptoms

• Gearbox warning light or malfunction indicator lamp on
• Harsh, delayed or flared gear changes
• Transmission stuck in a single gear (limp mode)
• Slipping or loss of drive in certain gears
• Poor fuel economy or reduced performance
• Erratic or unresponsive shifting

Possible causes

• Faulty transmission fluid pressure sensor or switch C reading high or stucklikely
• Damaged, chafed or corroded wiring or connector on the sensor circuit, including a short to voltagelikely
• Open circuit on the sensor signal return or ground, giving a high readingpossible
• Incorrect, degraded or contaminated transmission fluid, or wrong fluid level affecting the readingspossible
• Actual hydraulic pressure problem, such as a sticking valve body solenoid or pressure regulator, or a worn pumppossible
• Fault in the transmission control module or its internal wiring (on mechatronic units, the integrated electronics)rare

How to diagnose

1. Read all stored codes and freeze frame data, noting gear, temperature and speed when the fault set, and check for related transmission or electrical codes
2. Check the transmission fluid level and condition, following the manufacturer's procedure for the model, as some are sealed units needing specific temperature and tools
3. Inspect the sensor wiring and connectors for damage, chafing, fluid ingress, corrosion and bent or pushed-back pins
4. Using live data, compare the sensor reading with expected values at key off, idle and in each selector position, and see whether it sits at a fixed high value
5. Check the sensor supply voltage, signal and ground at the connector with a multimeter against the manufacturer's wiring diagram, testing for a short to voltage or an open ground
6. Check for a short to voltage by unplugging the sensor and seeing whether the signal changes, then test the wiring between sensor and control module for continuity
7. Look up technical service bulletins and software updates for the vehicle and transmission
8. If the electrical side is sound, carry out a hydraulic pressure test per the manufacturer's procedure to see whether the pressure is genuinely abnormal

How to fix

• Replace the faulty pressure sensor or switch if it is confirmed defective
• Repair or replace damaged wiring and connectors, correcting any short to voltage or open ground
• Correct the fluid level, or replace the fluid with the specified type if it is degraded or contaminated
• Repair or replace the valve body, solenoids or pressure regulator if the hydraulic pressure is found to be abnormal
• Update the control module software if a known fault and a manufacturer update exist, or repair or replace the module if it is confirmed faulty

Can I keep driving?

Nearby codes

• P0872GenericTransmission Fluid Pressure Sensor/Switch C Circuit Low
• P0874GenericTransmission Fluid Pressure Sensor/Switch C Circuit Intermittent