P25B7
Auxiliary Ignition Switch On/Start Position Circuit
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.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Open or shorted wireCommon
Parts involved
- Auxiliary Ignition Switch
- Wiring Harness
P25B7 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.