P05BD: Stop-Start Mode Switch Circuit Range or Performance

What it means

Same as P05BC with the input in plausible range yet not matching the expected toggle behaviour - typically a worn switch contact.

At a glance

• Usually lights the check-engine light

How it works

The stop-start mode switch sends the driver’s enable or disable request to the control module. P05BD sets when the switch signal is within a plausible electrical range but does not change as expected when the driver toggles the switch.

Common causes

Most likely first.

1. Worn or faulty switch contacts
2. Loose or corroded switch connector
3. Damaged switch wiring

Symptoms

• Check-engine light
• Stop-start mode may not respond consistently to the switch
• Stop-start may remain enabled or unavailable

How to diagnose it

1. Use a scan tool to watch the stop-start switch status while pressing it several times, checking whether the reported state changes consistently.
2. Inspect the switch for sticking or wear and check its connector for looseness or corrosion.
3. Inspect the switch wiring for damage or intermittent contact, moving the harness gently while monitoring the scan-tool status.
4. Test the switch contacts and signal circuit for consistent operation using the manufacturer’s procedure.
5. If the switch and wiring behave correctly, check the receiving module’s input and configuration for a fault.

Common fixes

• Clean or secure a loose or corroded switch connector.
• Repair damaged or intermittent switch wiring.
• Replace a worn or faulty stop-start mode switch.
• Repair or replace the receiving module if its input is confirmed faulty.

Can I keep driving?

The fault usually affects stop-start mode selection rather than normal driving, but the system may ignore the switch or behave inconsistently. Do not assume stop-start is disabled unless the vehicle confirms the selected mode.