Chassis, generic

C066F Service/Park Brake Chamber Pressure Too Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C066F reports chamber pressure below what the brake system needs. No maker documents this code. For the spring section the consequences are clear: inside Bendix's piggyback unit the main spring starts to apply the brake once its chamber pressure falls under 78 psi, so a leak or weak supply makes the brakes drag. UN Regulation 13 requires that the springs of a motor vehicle do not start acting above 80 % of the lowest normal pressure, and that the driver is warned when the feed to the spring chamber sinks far enough for the brake components to start moving. FMVSS 121 asks for a warning once the service reservoir falls below 60 psi. Haldex lets its trailer EBS monitor spring brake pressure through an extra 5 V sensor and light a lamp under a set limit.

Likely causes

Leaking diaphragm, chamber seal or supply line
Insufficient reservoir pressure from compressor or dryer
Park valve or relay valve not delivering full pressure

Symptoms

  • Red brake or low-air warning, parking brake indicator flashing
  • Brakes dragging or spring brakes applying on their own

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,200
Time0.5–4 h

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

Parts involved

service park brake chamberair compressorair lines

Related codes

C066DC066E

References: static.nhtsa.gov, mlit.go.jp, law.cornell.edu, haldex.com.