Chassis, generic

C05AA ABS Pump Motor Temperature Too High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C05AA signals that the ABS return or high-pressure pump motor, or its switching stage, has become too hot. Few units have a sensor on the motor, so the temperature is usually modelled. A Kelsey-Hayes (now ZF) patent estimates the heat of the transistor that drives the pump from separate heating and cooling curves, starting from the module's ambient sensor; above a limit of about 90–150 °C (60–110 °C in deep cold) the pump is disabled until the estimate falls below a lower threshold, optionally with a warning lamp. Bosch describes a staged response in an electrohydraulic brake: as limits are passed, heat-producing functions are cut back down to the mechanical fallback. Long ABS or stability events, hot climates and a stiff pump favour it. No manufacturer publishes C05AA.

Likely causes

Long ABS, traction or stability interventions, e.g. on rough or slippery roads
Stiff pump or worn motor brushes raising current and heat
High under-hood or ambient temperature
Module ambient sensor or temperature model giving false values

Symptoms

  • ABS or stability control temporarily unavailable
  • ABS or brake warning lamp on, often clearing after cooling down

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–2,000
Time0.3–3 h

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

Parts involved

abs pump motorabs hydraulic unit

Related codes

C052BC052DC05AEC055B

References: patents.google.com, patents.google.com, static.nhtsa.gov.