Network, generic

U027A Lost Communication With Battery Charger Control Module C

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Module C is a third on-board charger in the same vehicle; A and B have U019B and U01BB. Several chargers on one bus need clearly separated roles, and a Lear patent shows one way: each unit reads a coded input at start-up, then joins the vehicle bus either as master with the master message set or as slave with the slave set. A slave whose input or wiring is wrong can thus vanish from the network. U027A is stored when the supervising controller stops hearing charger C. No manufacturer documents the code publicly or names a third charger. For plug-in hybrids CARB only asks for detection of charger faults that stop charging or reduce the charging rate. AC charging then usually runs slower; driving and emissions are not affected.

Likely causes

12 V supply or wake-up line of charger C missing
Bus connector at charger C corroded or not latched
Charger C coded or addressed wrongly after replacement
Charger C control electronics faulty

Symptoms

  • Reduced AC charging power or longer charging time
  • Charging fault message

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–2,500
Time0.5–4 h

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

Parts involved

on board chargervehicle bus wiring

Related codes

U027BU057BU019BU01BB

References: patents.google.com, law.cornell.edu.