Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
What does P0871 mean?
The P0871 code means the vehicle's onboard diagnostic system has detected: Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance. This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Shifting irregularities in higher gears
- Occasional transmission slip
- Inconsistent shift quality
Probable Causes (Ranked by Likelihood)
- Pressure sensor C reading outside expected range for conditions Very High
- Degraded transmission fluid affecting pressure readings High
- Partial blockage in sensor C hydraulic passage Moderate
- Internal valve body wear Low
Step-by-Step Diagnostic Procedure
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Compare sensor C reading to a mechanical pressure gauge at the C tap
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Perform a transmission fluid and filter service
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Monitor sensor C data at various RPMs and loads
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Check for manufacturer TSBs regarding sensor C calibration
Frequently Asked Questions
What causes range/performance issues on sensor C?
The sensor provides a voltage within the valid range but the pressure value does not match what the TCM expects. Dirty fluid, a partially blocked passage, or a worn pump can cause this.
Is a fluid change a good first step?
Yes, a transmission fluid and filter service is a low-cost first step that can resolve pressure irregularities caused by degraded fluid.
Can P0871 cause drivability issues?
Yes, if the TCM receives inaccurate pressure data from sensor C, it may make incorrect shift decisions, leading to slip, flare, or harsh shifts.