What it means
The transmission control module monitors circuit B for the transmission range control signal. It sets this code when the circuit is detected as open, interrupting the expected signal.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Transmission range control circuit B carries a signal used to identify or control the selected transmission range. The transmission control module monitors this circuit and sets P27E7 when it detects an open path, interrupting the expected range signal and potentially making the selected gear unclear.
Common causes
Most likely first.
- Open or damaged wiring
- Loose or corroded connector
- Fault in the range-control circuit
Symptoms
- Transmission warning light
- Incorrect gear indication or difficulty selecting a range
- Limited shifting or limp mode
How to diagnose it
- Record freeze-frame data and check scan-tool range data against the gear selected at the lever to see whether circuit B's signal is missing.
- Inspect the range-control B connector and harness for a loose plug, corrosion, damaged pins, or broken wiring.
- Check continuity through circuit B and its connectors for an open, following the manufacturer's wiring diagram and safe isolation procedure.
- Operate the selector through its positions while monitoring range data to see whether the circuit signal returns or drops out.
- If wiring continuity is intact, test the range-control component and module terminals using the manufacturer's diagnostic procedure.
Common fixes
- Reconnect and secure a loose range-control B connector.
- Clean corroded terminals and repair damaged connector pins.
- Repair an open wire in the range-control B circuit.
- Replace the failed range-control component if testing confirms its circuit B output is open.
Can I keep driving?
Do not drive if the indicated range disagrees with the selector, the vehicle will not reliably select Park or Drive, or shifting is limited; the transmission may respond unpredictably. Arrange prompt diagnosis, and use towing if the vehicle cannot be placed securely in Park.
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.