Chassis, generic

C05A8 ABS Pump Motor Supply Voltage B Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C05A8 means supply B is present but behaves implausibly: it sags too far once the pump starts, recovers too slowly, or does not match the state the module has commanded. That is different from a hard open (C05A5) or a steady high or low reading (C05A6, C05A7). No maker publishes a threshold for C05A8. Ford's hybrid brake module shows the logic on its single pump feed under C052B: below 6 V with the pump off or below 7.3 V with it on, each for 1.8 s. Mitsubishi lists 10–16 V for the motor feed on the 2023 Outlander PHEV, measured once with the motor switch off and once on. Systems with a second feed, such as the redundant brake-by-wire drive in an Ipgate patent, need this check to know whether the backup path is really usable. Load-test battery and feed.

Likely causes

Excessive voltage drop in the B feed when the pump starts
Relay or semiconductor switch in the B path responding slowly or partly
Aged 12 V battery with high internal resistance

Symptoms

  • Intermittent ABS/ESC warning, mostly during pump activity
  • Message about reduced braking redundancy on brake-by-wire vehicles

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–1,200
Time0.5–3 h

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

Parts involved

abs pump motor supply b

Related codes

C05A5C05A6C05A7C05A9C055CC052B

References: fordservicecontent.com, mitsubishitechinfo.com, patents.google.com.