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U040B Invalid Data Received From Exhaust Gas Recirculation Control Module A

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U040B refers to an exhaust gas recirculation system driven by its own electronics on the bus, for example a smart EGR valve actuator that receives position targets and returns its measured position. The code is set when that unit's replies reach the engine controller but fail plausibility or protection checks, so the controller can no longer verify how much exhaust gas flows back. U040B appears in no public manufacturer document and in none of the bulletins indexed by NHTSA. GM's 2025 tables show how such checks work on other emission-related modules: counter, protection value and checksum, a fail ratio such as 8 of 18 samples, then a MIL. CARB requires EGR flow to be monitored, so the code counts as emission-relevant; expect EGR to be switched off, higher NOx and possibly less power. U010A is lost contact, U040C module B.

Likely causes

Electronics or position sensor of the EGR actuator A delivering implausible values
Heat-damaged connector or bus line at the EGR unit
Software of engine controller and EGR module A out of step
EGR control module A internally faulty

Symptoms

  • Check engine light
  • Reduced power or rough idle
  • EGR flow codes stored alongside

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 a

Related codes

U010AU040CP0400P0401

References: law.cornell.edu, gsi.ext.gm.com, en.wikipedia.org.