Powertrain, generic · Auxiliary emission controls

P04D7 Exhaust Brake Input Circuit Intermittent/Erratic

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. P04D7 means the signal changes state abruptly or too often, or shows brief excursions too short for the low/high codes – bouncing contacts or a loose connection.

Likely causes

Loose contact at the button or module connector
Worn or bouncing button
Chafed wire with intermittent short
Moisture or corrosion

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

P04D3P04D4P04D5P04D6P0479

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