P04D4Exhaust Brake Input Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The exhaust brake input is the driver's request for the exhaust or engine brake – a button or stalk on diesel pick-ups and trucks. On GM's 6.6-litre L5P, for example, the button must be pressed again after every start. GM uses the exhaust brake status as an enable condition for other emission monitors, which is why CARB requires the input to be checked. No manufacturer table available to us lists P04D3–P04D7; Hino's J08E truck engine checks P04D5 before its exhaust brake function test. P04D4 is the plausibility fault: the signal is electrically valid but does not fit the operating state – for example a button reporting pressed for an unusually long time, or a lever coding between two stages.
- What you may notice
- Exhaust brake cannot be switched on, button lamp off or wrong
- Possibly check engine light
- More load on the service brakes downhill
- Likely causes
- LikelyButton mechanically stuck or contact dirty (permanently pressed)
- PossibleContact resistance in connector or ground (voltage between thresholds)
- RareWrongly retrofitted or coded button or lever
- RareEngine module or software
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.