What it means
The transmission control module monitors the park position sensor or switch B signal for stable operation. It sets this code when the signal fluctuates, drops out, or changes erratically instead of tracking park position consistently.
At a glance
- Usually lights the check-engine light
How it works
The transmission control module expects park-position switch B to provide a stable signal as the selector moves. This code sets when that signal drops out or changes erratically instead of tracking position consistently.
Common causes
Most likely first.
- Switch contact bounce
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
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
- Check freeze-frame and live transmission data for the selector position and B signal at the time the fault occurred.
- While the vehicle is safely parked, move the selector through its positions and watch for the B reading to flicker or drop out.
- Inspect switch B and its connector for loose or corroded contacts, then check whether the harness is rubbing against or vibrating near another component.
- With the wiring diagram, check continuity and connection stability in the B circuit while gently moving the harness and connector.
- If the circuit remains stable, test switch B for erratic contact operation and check the module input against the manufacturer's specification.
Common fixes
- Reseat and secure the switch B connector to restore stable contact.
- Clean or repair corroded or loose connector terminals.
- Repair and reroute a chafed or vibration-prone section of the B harness.
- Replace switch B if its contacts continue to drop out.
- Repair the transmission control module input circuit if the switch and wiring test correctly.
Can I keep driving?
Avoid unnecessary driving if the signal loss causes missed shifts or an unpredictable gear; stop if control becomes unreliable. Intermittent faults can worsen and may leave the transmission in a limited operating mode.
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.