Chassis, generic

C066E Service/Park Brake Chamber Pressure Too High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

C066E means the measured chamber pressure is higher than the module allows in the present state. No maker documents the code, so its limit is not public. Too much pressure in the service section raises the push on the brake directly: Bendix calculates about 1,800 lbf on the pushrod when 60 psi reaches a type 30 chamber, and its chamber tests are not to exceed 120 psig. A specific risk is compounding. A ZF patent from the WABCO family explains that adding service brake force on top of applied spring brakes can permanently damage downsized brakes, and uses the axle's service pressure to release the springs before that happens. Haldex's trailer EBS warns separately when reservoir pressure rises above 9.8 bar, pointing to a governor or valve fault upstream.

Likely causes

Governor or pressure regulator letting system pressure rise too far
Anti-compound function not working, both forces add up
Pressure sensor reading too high

Symptoms

  • Brake warning or fault message on the dash or trailer lamp
  • Harsh braking or overheated wheel ends after parking manoeuvres

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,500
Time0.5–4 h

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

Parts involved

service park brake chamberservice park brake chamber pressure sensorair compressor

Related codes

C066DC066F

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