Powertrain, generic · Auxiliary emission controls

P04D3 Exhaust Brake Input Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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. P04D3 is the general circuit fault of the request input, used where the module cannot resolve the fault type further – an open circuit or, on bus-connected buttons, an invalid message.

Likely causes

Exhaust brake button faulty (contact, lighting board)
Open wire or connector between button and module
Fault in an intermediate module or bus message
Engine module or software

Symptoms

  • Exhaust brake cannot be switched on, button lamp off or wrong
  • Possibly check engine light
  • More load on the service brakes downhill

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–300
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

exhaust brake switchswitch wiringengine control module

Related codes

P04D4P04D5P04D6P04D7P0475

References: static.nhtsa.gov, static.nhtsa.gov, gsi.ext.gm.com, law.cornell.edu.