What it means
Same as P05BC with the signal shorted to supply. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The stop-start mode switch sends the driver’s mode request to the control module through a signal circuit. P05BF sets when that signal is too high, often because the signal wire is shorted to a power supply, and the module may not recognize the switch position.
Common causes
Most likely first.
- Signal shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check-engine light
- Stop-start mode may not respond to the switch
- Stop-start may remain enabled or unavailable
How to diagnose it
- Use a scan tool to monitor the stop-start switch input and confirm that it stays high while the switch is operated.
- Inspect the switch connector and harness for chafing, pinched wires, moisture, corrosion, or a terminal pushed back in the connector.
- Check nearby wiring and connectors for contact between the switch signal wire and a power-supply wire.
- With the circuit isolated as specified by the manufacturer, check the signal wire for a short to supply.
- If the wiring is sound, test the switch output and control-module input for a component fault.
Common fixes
- Repair signal wiring that is pinched or shorted to a supply wire.
- Clean or repair corroded connector pins and restore proper terminal fit.
- Replace a faulty stop-start mode switch if its output is confirmed high.
- Repair or replace the control module if its input is confirmed faulty.
Can I keep driving?
The fault usually affects stop-start mode selection rather than basic engine operation, but the system may ignore the switch or remain in its default mode. Avoid relying on the switch to disable stop-start until the circuit is repaired.
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.