What it means
The transmission fluid pressure sensor/switch C reports a circuit low fault. Hydraulic pressure feedback for shift control is unreliable on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Transmission pressure sensor/switch C sends a pressure-related electrical signal to the control module for shift control. P0872 sets when the C-channel circuit voltage is lower than the module expects, which can result from a grounded signal wire, a shorted sensor, or a poor connector connection.
Common causes
Most likely first.
- Signal wire shorted to ground
- Internal sensor short
- Connector pins corroded - high contact resistance
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Save freeze-frame data and inspect live sensor C data to confirm the low reading and note whether it appears with a particular gear or operating condition.
- Inspect sensor C's connector and harness for corrosion, damaged insulation, and wiring pinched against the transmission or chassis.
- Check the connector pins for corrosion or poor contact, then make sure the connector is fully seated.
- Using the vehicle wiring diagram, test the sensor C signal wire for a short to ground and check its reference and ground circuits against the manufacturer's specification.
- If wiring and connector tests pass, test pressure sensor/switch C and replace it only if its output remains low under the specified test conditions.
Common fixes
- Clean corroded connector pins and secure the sensor C connector.
- Repair a signal wire short to ground or other damaged wiring in the C circuit.
- Replace pressure sensor/switch C if it is internally shorted and the wiring checks out.
- Repair the connector or terminal that is preventing a sound electrical connection.
Can I keep driving?
Limit driving and avoid towing or hard acceleration, especially if shifts are harsh, slipping, or the transmission is in limp mode. A low C-circuit signal can disrupt shift control and continued slipping can damage the transmission.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.