What it means
General electrical fault on the auxiliary ignition switch On/Start input. Used on commercial vehicles or upfit applications where a second ignition switch (in a sleeper cab, work platform or crew compartment) can crank the engine.
At a glance
- Usually lights the check-engine light
How it works
The auxiliary ignition switch provides a Run/Start input so a second station, such as one in a commercial vehicle’s sleeper cab or work area, can request engine operation. The controller monitors this input circuit and sets this code when it detects a general electrical fault that prevents the auxiliary switch signal from being read correctly.
Common causes
Most likely first.
- Open or shorted wire
Symptoms
- Auxiliary ignition or start function may be unavailable
How to diagnose it
- Use a scan tool to check for related codes and view the auxiliary ignition switch input while operating the switch, if live data is available.
- Confirm the main ignition switch starts the vehicle and establish whether the fault affects only the auxiliary station’s Run/Start function.
- Inspect the auxiliary switch, its connector, and the accessible harness for loose connections, corrosion, damage, or a wire pulled out of its terminal.
- Check circuit continuity and for shorts between the auxiliary switch and the controller using the vehicle wiring diagram and manufacturer’s procedure.
- If the wiring and switch test correctly, test the controller input and output circuit as directed by the manufacturer before considering module repair.
Common fixes
- Reconnect a loose auxiliary ignition switch connector or terminal.
- Repair an open or damaged wire in the auxiliary Run/Start circuit.
- Replace a faulty auxiliary ignition switch after confirming its circuit is intact.
- Repair the affected module circuit only if testing confirms an internal fault.
Can I keep driving?
The vehicle may remain usable from its primary ignition switch, but the auxiliary start function could fail when needed. Do not rely on that station to start or operate the vehicle until 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.