Transmission Fluid Pressure Sensor/Switch D Circuit High
What does P0878 mean?
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.
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
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Measure voltage at sensor D connector with key on
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Check for an open ground at the sensor
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Test for short to battery voltage on the signal wire
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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.