Powertrain, generic (extended)

P2C3A Cylinder Head Temperature Sensor B Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2C3A reports that the signal of cylinder head temperature sensor B sits below the lowest voltage the module accepts. Because these sensors are NTC thermistors, a very low voltage would stand for an impossibly hot head, so the usual reasons are a signal wire shorted to ground, water inside the plug or a sensor with an internal short. No manufacturer publicly documents this code. Ford's monitor for its first sensor shows the method: under 0.244 V for 5 seconds, checked continuously, sets the low-input code (P017C, older P1290). The ECM then has to substitute a value, and some calibrations play it safe with full fan operation or a warning. Expect a false overheat message or reduced power. High input is P2C3B, plausibility P2C39.

Likely causes

Signal wire of sensor B chafed through to ground
Moisture or coolant in the sensor connector
Internal short in the thermistor of sensor B

Symptoms

  • Overheat warning or very high head temperature in live data on a cold engine
  • Cooling fans running at full speed without reason
  • Check engine light, possibly reduced engine power

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–350
Time0.3–2 h

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

Parts involved

cylinder head temperature sensor bwiring harnessecm

Related codes

P2C38P2C3BP2C39P2C3CP017C

References: law.cornell.edu, fordservicecontent.com, static.nhtsa.gov.