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U05AA Invalid Data Received From Charge Air Cooler Coolant Pump

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Engines with a water-cooled charge air cooler use an electric pump, often a LIN slave of the engine controller, to move coolant through the low-temperature circuit. CARB requires the charge air cooling to be checked for performance and its electronic parts to be monitored. U05AA is set when the pump reports speed, current or fault bits that do not make sense. Public maker documentation exists for the partner U02A9: GM's 2025 tables declare lost LIN contact after 2.5 s without a pump response, Type A; Ram 1500 owners see a check engine light with U02A9 and P023B from pushed-out terminals at the pump connector; Mercedes links U02A900 on GLC and GLE to the PTCU software or LIN wiring. None documents U05AA itself. Expect reduced boost if intake air runs hot.

Likely causes

Pushed-out or corroded terminals at the pump connector
Fault elsewhere on the shared LIN bus or in the master module software
Pump electronics or motor faulty

Symptoms

  • Check engine light on
  • Reduced engine power in hot conditions
  • Coolant warning or radiator fan running at full speed

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–600
Time0.3–2 h

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

Parts involved

cac coolant pump

Related codes

U02A9P023B

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