What Does P0870 Mean?
The TCM has detected a general malfunction in the transmission fluid pressure sensor/switch 'C' circuit. This sensor monitors hydraulic pressure in a specific transmission circuit and the TCM is receiving a signal that is outside expected parameters. The 'C' designation indicates a third pressure sensor circuit, typically monitoring a specific clutch pack or gear application pressure.
Common Causes
35%
Faulty transmission fluid pressure sensor/switch 'C'
25%
Damaged or corroded wiring to sensor 'C'
20%
Poor electrical connection at sensor or TCM connector
12%
Internal transmission issue affecting pressure in circuit 'C'
8%
TCM internal fault
Diagnostic Steps
1
Retrieve freeze frame data to determine the operating conditions (gear, RPM, temperature) when the fault occurred.
2
Back-probe the pressure sensor 'C' connector and verify the reference voltage (typically 5V) and ground integrity.
3
Monitor the live data PID for pressure sensor 'C' and verify the signal responds logically to throttle input and gear changes.
4
Inspect the sensor connector and transmission case connector for corrosion, backed-out pins, or fluid intrusion.
5
If the electrical circuit tests good, remove and inspect the pressure sensor for physical damage or contamination.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The TCM has detected a general malfunction in the transmission fluid pressure sensor/switch 'C' circuit. This sensor monitors hydraulic pressure in a specific transmission circuit and the TCM is receiving a signal that is outside expected parameters. The 'C' designation indicates a third pressure se...
The most common cause of P0870 (Transmission Fluid Pressure Sensor/Switch "C" Circuit) is: Faulty transmission fluid pressure sensor/switch 'C'
Typical repair costs for P0870 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive cautiously. The transmission may default to a limited operating strategy with firm shifts. Avoid heavy loads and prolonged highway driving until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0870 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Hydraulic Pressure Monitoring
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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