P0878 moderate

Transmission Fluid Pressure Sensor/Switch D Circuit High

The P0878 code means the vehicle's onboard diagnostic system has detected: Transmission Fluid Pressure Sensor/Switch D Circuit High. This is a moderate severity code.

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Keep driving?: Short distances only
DIY difficulty: hard
Estimated cost: $100 - $500 (parts and labor)

Check Your Fluid First

ANCEL AD310 OBD-II Scanner

Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.

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Read Transmission Codes

LAUNCH CRP123X (Reads All Systems)

Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.

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Common Symptoms

Check Engine Light illuminated
Harsh shifting in certain gear ranges
Firm engagement when selecting gear
TCM may restrict available gears

Probable Causes (Ranked by Likelihood)

Open ground at pressure sensor D Very High
Faulty pressure sensor D stuck reading high High
Short to voltage in sensor D signal wire Moderate
TCM reference voltage fault for sensor D Low

Step-by-Step Diagnostic Procedure

Measure voltage at sensor D connector with key on
Check for an open ground at the sensor
Test for short to battery voltage on the signal wire
Replace sensor D if circuit checks pass

Frequently Asked Questions

Is P0878 the high counterpart of P0877?

Yes, P0877 indicates sensor D signal is too low, and P0878 indicates it is too high. They represent opposite electrical conditions in the same circuit.

Can an open ground wire be hard to find?

Open grounds can be tricky because the wire may look intact externally but be broken internally. A continuity test with a multimeter is needed to confirm.

Will the transmission work normally if sensor D reads high?

The TCM may make incorrect shift decisions based on the false high reading. Shift quality will be degraded and the TCM may limit gear selection as a protective measure.