Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P05C4 Engine Coolant Pressure Sensor Circuit Low

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

An engine coolant pressure sensor (5 V reference, ratiometric signal) measures pressure in the cooling circuit; in a sealed circuit pressure rises with temperature, so deviations reveal leaks or a loose cap – described in Navistar and GE patents for commercial and rail engines. No manufacturer document available to us uses P05C2–P05C6 for passenger cars; CARB requires input components to be checked for circuit faults, range and plausibility. P05C4 means the signal voltage is below its limit – usually a signal shorted to ground, an open signal line or a missing 5 V reference, not low coolant pressure.

Likely causes

Signal line shorted to ground or open
5 V reference open or shorted
Sensor faulty
Connector corroded

Symptoms

  • Check engine light or warning (depending on the maker)
  • Coolant pressure or leak warning unavailable
  • Usually no change in driving

Repair estimate

DifficultyEasyDIY possible
Parts and labour€50–300
Time0.3–1.5 h

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

Parts involved

coolant pressure sensorsensor wiringengine control module

Related codes

P05C2P05C3P05C5P0117P2560P0217

References: law.cornell.edu, patents.google.com, patents.google.com.