What it means
The ECM detects a circuit low fault on the clutch position sensor b circuit. Reading cannot be used reliably for control.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Clutch position sensor B sends a position signal through its circuit to the control module for shift coordination. The module sets P087C when that signal is pulled below its expected range, so it cannot reliably determine clutch position.
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 check live data for sensor B; confirm whether its reading stays unusually low or drops when the fault occurs.
- Inspect the sensor B connector and harness for chafing, pinched insulation, moisture, or corrosion that could short the signal to ground.
- With the circuit isolated as directed by the manufacturer's service information, check whether the signal wire is shorted to ground.
- Check the connector terminals for corrosion or poor contact and verify the sensor's ground and reference circuits against the manufacturer's specification.
- If the wiring and connections are sound, test clutch position sensor B for an internal short and replace it if it fails the manufacturer's specification.
Common fixes
- Clean and properly secure the sensor B connector if contamination or poor seating is found.
- Repair a signal wire shorted to ground.
- Replace corroded or damaged connector terminals.
- Replace clutch position sensor B if it is internally shorted.
Can I keep driving?
Avoid driving if shifts are delayed, harsh, or missing, or if the transmission enters limp mode; arrange a safe route to repair. Continued operation with a falsely low clutch signal can disrupt shifts and increase clutch or transmission wear.
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.