P04D4
Exhaust Brake Input Circuit Range or Performance
Same as P04D3 with the signal in plausible range yet not matching expected behaviour - e.g. activation request without driver input or no response after a request.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Signal implausible against driver action or busCommon
Parts involved
- Exhaust Brake Request Switch
P04D4 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.