P2B73Coolant Heater A Control Circuit Low
- Generic OBD-II code · Powertrain
- How the car detects it
- P2B73 is the low case on the command circuit of coolant heater A: the commanding module reads the line at or near ground when it expects a higher level. Usual reasons are a chafed wire touching body ground, coolant or water in a connector, or an input in the heater that pulls the line down. Hyundai and Kia patent US11378000B2 shows why the line carries only a request: the heater has its own controller, which switches several sheath elements one by one and protects them. No manufacturer documents P2B73 publicly, and no thresholds are known. Under CARB rules, commanded outputs like this must be watched for circuit faults. The heater then normally stays off; an electrified car may start its engine more often for cabin heat. Open circuit is P2B72, high voltage P2B74.
- What you may notice
- Coolant heater does not switch on, weak cabin heat
- Engine runs more often in the cold (hybrids)
- Fuse for the request circuit may blow repeatedly
- Likely causes
- LikelyCommand wire chafed through and shorted to ground
- PossibleCoolant or water in the heater connector
- PossibleInput of the heater electronics shorted internally
- RareCommanding module cannot drive the line high
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.