What it means
Cruise Control/Brake Switch B Circuit Low: the signal voltage is below the expected range. This affects cruise-control operation.
At a glance
- Usually lights the check-engine light
How it works
Brake-switch circuit A supplies a brake-pedal state that the control module uses for cruise cancellation and, on some vehicles, shift interlock. This low-circuit code means the A signal is below its expected electrical range, which can happen with a short to ground, a faulty switch, or a poor connection.
Common causes
Most likely first.
- Brake switch defective
- Wiring shorted to ground
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light may come on
- Cruise control may not engage or may disengage unexpectedly
- Brake lights may stay on or fail to illuminate
- Shift interlock may not release on vehicles that use this signal
How to diagnose it
- With the vehicle parked, check whether the brake lights remain on or fail to illuminate as the pedal is pressed and released.
- Use a scan tool to monitor brake-switch A while operating the pedal and confirm whether its reported state stays low or fails to change.
- Inspect the brake switch at the pedal and its connector for misadjustment, corrosion, loose terminals, or damage.
- Check the A signal wire for a short to ground, chafing, or damaged insulation, and inspect its power and ground paths using the wiring diagram.
- Measure the A circuit and switch operation against the manufacturer's specification to distinguish a failed switch from a wiring fault.
Common fixes
- Correct brake-switch adjustment if it is preventing the A signal from changing.
- Clean and secure corroded or loose connector terminals.
- Repair a signal wire shorted to ground or other damaged A-circuit wiring.
- Replace the brake switch if it produces a low signal despite correct wiring and adjustment.
- Repair an affected module connection if the switch and harness test correctly.
Can I keep driving?
Verify that the brake lights work before driving; if they fail or stay on, do not drive until repaired. Avoid cruise control, since it may not engage or may disengage unpredictably, and the shift interlock may be affected on some vehicles.
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.