Powertrain, generic (extended)

P2B72 Coolant Heater A Control Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2B72 says the command line to coolant heater A is open or has lost continuity. Keep it apart from the engine coolant heater family P01E8–P01EF: the other J2012 codes for this heater – internal module, supply voltage and over-temperature under P2DA4–P2DA7, lost communication under U069E – point to a unit with its own electronics, such as the electric coolant heater of hybrids and EVs. GM's 2013–2014 Volt used a separate coolant heater control module for this job (bulletin PIC5943, no cabin heat in electric mode). No manufacturer documents P2B72 publicly, so limits and timing are unknown. CARB 13 CCR 1968.2 requires circuit monitoring of commanded outputs. In winter the cabin stays cold, or an engine runs more often to supply heat.

Likely causes

Command wire to the heater broken or connector not latched
Terminal pushed back or corroded in the heater connector
Input stage of the heater electronics open internally
Output stage in the commanding control module faulty

Symptoms

  • Little or no cabin heat, especially in electric driving
  • Engine starts more often in cold weather to provide heat (hybrids)
  • Warning or fault message, depending on the manufacturer

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–900
Time0.5–3 h

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

Parts involved

coolant heater awiring harnessecm

Related codes

P2B73P2B74P2B75P2B76P01E8U069E

References: law.cornell.edu, static.nhtsa.gov, patents.google.com.