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U028A Lost Communication With Transmission Fluid Pump Module B

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

An electric transmission fluid pump with built-in electronics holds clutch pressure and lubrication whenever the engine is stopped, in auto stop or electric driving. Module B is a second pump of this kind; U028A means the transmission or hybrid controller no longer hears its status frames. No manufacturer documents U028A or names a pump B publicly, so the reaction must be inferred from pump A. Stellantis calls that unit transmission fluid pump module 1 and ties U0287 on the Wrangler and Grand Cherokee 4xe to a failed in-pan pump with MIL and limp mode (21-041-26). Hyundai stores U028700 in the transmission unit of the Santa Fe and Tucson without any warning lamp and merely blocks Idle Stop and Go (26-AT-002H). For B, expect stop-start or electric drive to be withdrawn.

Likely causes

Electric pump B or its integrated electronics failed
Corroded or loose pump connector, oil wicking into the connector
Supply, ground or bus line to pump B interrupted
Transmission controller software outdated

Symptoms

  • Start-stop function no longer active
  • Electric driving blocked or engine keeps running
  • Transmission warning, harsh engagement after an engine stop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,000
Time0.5–5 h

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

Parts involved

transmission fluid pump module bvehicle bus wiring

Related codes

U0287U058BU0588P0B0DP2797

References: static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.