P0870 moderate

Transmission Fluid Pressure Sensor/Switch C Circuit

The P0870 code means the vehicle's onboard diagnostic system has detected: Transmission Fluid Pressure Sensor/Switch C Circuit. This is a moderate severity code.

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Keep driving?: Short distances only
DIY difficulty: hard
Estimated cost: $150 - $600 (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
Erratic shifting in specific gears
Transmission slip during certain shift events
Possible limp mode

Probable Causes (Ranked by Likelihood)

Faulty transmission fluid pressure sensor C Very High
Wiring fault in pressure sensor C circuit High
Corroded connector at sensor C Moderate
Internal valve body issue affecting sensor C circuit Low

Step-by-Step Diagnostic Procedure

Check transmission fluid level and condition
Monitor pressure sensor C data on a scan tool and compare to sensors A and B
Inspect wiring and connector at pressure sensor C
Test sensor C resistance and compare to manufacturer specifications

Frequently Asked Questions

Why does my transmission have three pressure sensors?

Modern transmissions with 8 or more speeds use multiple pressure sensors to monitor different hydraulic circuits. Sensor C typically monitors a third pressure circuit for additional shift control precision.

Is sensor C diagnosed the same way as A and B?

Yes, the diagnostic approach is the same: check fluid level, monitor sensor data, inspect wiring, and compare readings to specifications.

Are all pressure sensors the same part?

Not always. While some vehicles use identical sensors in all positions, others use different sensors calibrated for different pressure ranges. Always verify the correct part number.