Chassis, generic

C0640 Brake Pressure Sensor J Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

C0640 marks sensor J as valid in voltage but wrong in content. In plunger-based brakes the pressure can be cross-checked against what the actuator did: Ipgate compares delivered piston volume with the pressure-volume curve and closes the inlet valves one by one to find a leaking circuit, while Continental's one-box layout carries separate sensors for master cylinder and pressure supply that can be set against each other. GM's 2016 hybrid module re-zeroes its wheel pressure sensor only while the pedal is released and reports a correction larger than ±1,500 kPa. A circuit leak, air or a seized valve can therefore set C0640 as well as a drifting sensor. No maker documents this code publicly; PIP5094 lists C0640 under GM's old numbering.

Likely causes

Sensor J drifting so its zero correction exceeds the limit
Leak or air in the brake circuit so pressure and delivered volume disagree
Inlet or isolation valve seized

Symptoms

  • Brake warning and ESC lamps on
  • Longer pedal travel or reduced brake boost in fallback mode

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–2,000
Time0.5–4 h

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

Parts involved

brake pressure sensor j

Related codes

C063DC063EC063FC063CC0644C0578

References: patents.google.com, patents.google.com, gsi.ext.gm.com, static.nhtsa.gov.