Network, generic

U040C Invalid Data Received From Exhaust Gas Recirculation Control Module B

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U040C concerns a second, separately networked EGR control unit, B. Two units appear on engines with separate high- and low-pressure recirculation paths, common on modern diesels, or with one EGR valve per cylinder bank; which one counts as B is up to the maker. The engine controller logs U040C when module B keeps talking but its content fails validation, while module A may still deliver clean data, which narrows the search to B's branch. Public manufacturer material and the NHTSA bulletins are silent on U040C, so its limits are not known; checks of counter and checksum as in GM's 2025 tables are the common pattern. With one EGR path unverified the controller usually closes it, NOx rises, and the MIL is expected because CARB treats EGR as a monitored system. U010B is lost contact, U040B module A.

Likely causes

Electronics or position sensor of EGR actuator B delivering implausible values
Connector or bus line in the branch of module B damaged by heat or moisture
Module B with software that does not match the engine controller

Symptoms

  • Check engine light
  • Reduced power, more smoke or higher fuel consumption

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,200
Time0.5–3 h

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

Parts involved

egr module b

Related codes

U010BU040BP0400

References: law.cornell.edu, en.wikipedia.org.