Powertrain, generic (extended)

P2AC9 Charge Air Cooler Coolant Temperature Sensor B Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2AC9 reports that the signal of charge air cooler coolant temperature sensor B has dropped below its permitted window. These sensors are NTC thermistors, so a low signal stands for an implausibly hot coolant and usually means the signal wire touches ground or the element is internally shorted. Public limits exist only for sensor A: Ford's 2023 diesels flag P00E0 below 0.162 V within 5 s, while GM's 2025 diesel table reads resistance and fails under 70 ohms in 30 of 38 samples as a Type B code. A B-sensor check from the same maker is likely built the same way, but no document states it. With a false hot value the control may run the loop pump constantly or cut boost. Measure resistance at a known temperature and inspect the harness for chafing.

Likely causes

Signal wire of sensor B shorted to ground
Sensor B internally shorted
Coolant in the connector bridging the terminals

Symptoms

  • Check engine light on
  • Live data shows an extremely high coolant temperature for sensor B
  • Coolant pump of the loop runs constantly or boost is reduced

Repair estimate

DifficultyEasyDIY possible
Parts and labour€60–300
Time0.5–2 h

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

Parts involved

charge air cooler coolant temp sensor bwiring harnessecm

Related codes

P2AC7P2ACAP2AC8P2ACBP00E0

References: fordservicecontent.com, gsi.ext.gm.com, law.cornell.edu.