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Transmission Fluid Pressure Sensor/Switch C Circuit

Jump to the fix

Severity

High

Can I keep driving?

Avoid extended driving; visit a service soon.

First step

Common solutions to code P0879 could include the following- Inspection, testing, and replacement of the Transmission Fluid Pressure Sensor Inspection, and replacement/repair of damaged wiring Replacement of transmission fluid In rare cases, replacement/rebuilding of the transmission or transmission components such as the valve body In even more rare cases, replacement and programming of the PCM/TCM

  • PPowertrain
  • 0Generic code
  • 8Transmission
  • 70Sequence number

What does it mean?

OBD II fault code P0870 is a generic code that is defined as “Transmission fluid pressure (TFP) sensor / switch C -circuit malfunction”, and is set when the PCM (Powertrain Control Module) or TCM (Transmission Control Module) or both, detect a failure in the Transmission Fluid Pressure Sensor / Switch C Circuit.

Note that while this code refers primarily to malfunctions/failures in the Transmission Fluid Pressure Sensor’s control or signal circuit, this code can also set as the result of mechanical failures or issues in the transmission itself, or in the valve body assembly that controls gearshifts. All automatic transmissions depend on pressurized transmission fluid both to operate efficiently, and to make gearshifts smoother.

In terms of operation, the transmission uses an engine-driven pump to pressurize the fluid. The pressurized fluid is then directed into and out of complex hydraulic circuits via shift solenoids that are controlled by the TCM, and in a fully functional system, the PCM and TCM (and various other control modules) work in conjunction to control the shift solenoids to ensure smooth, predictable gearshifts.

To monitor the transmission fluid line pressure continuously, the transmission is fitted with a pressure sensitive sensor that converts the actual fluid pressure into an electrical signal. This signal is transmitted to the PCM/TCM and other affected control modules via the CAN (Controller Area Network) bus system to enable the PCM/TCM to control the transmissions’ shift pattern effectively based on operating conditions and driving style.

Thus, the input data from the Transmission Fluid Pressure Sensor is a critical factor in effective transmission control. Therefore, to protect the transmission and other drive train components, the PCM/TCM will set code P0870 when a fault, failure, or malfunction occurs in the Transmission Fluid Pressure Sensor’s control or signal circuit(s). In addition, the PCM/TCM may also illuminate a warning light, and initiate a fail-safe or limp mode to protect the transmission.

Symptoms

Likely causes

How to fix it

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.