Powertrain, generic · Auxiliary emission controls

P0408 EGR Sensor B Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. What EGR sensor B is depends on the manufacturer – on systems with a second valve or pressure sensor it is that second sensor. GM's diesels of 2017/18 use P0408 for the coolant temperature sensor at the inlet of the high-pressure EGR cooler: high means a resistance above 134 kΩ, i.e. an open circuit or extreme cold (20 of 24 samples, MIL after two trips). A substitute value is used.

Likely causes

Signal or ground wire open, connector off
Sensor faulty
Connector corroded (near coolant or exhaust)
Engine module input

Symptoms

  • Check engine light on
  • Usually no change in driving
  • EGR or EGR cooler protection possibly restricted

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–250
Time0.5–1.5 h

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

Parts involved

egr sensor begr cooler coolant temperature sensorsensor wiringengine control module

Related codes

P0407P0406P0405P044D

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.