P2B74Coolant Heater A Control Circuit High
- Generic OBD-II code · Powertrain
- How the car detects it
- P2B74 is the opposite of P2B73: the command circuit of coolant heater A sits at or near supply voltage while the module expects it low, or the output stage measures excess current and shuts down. A wire rubbed through onto a 12 V feed, a crushed harness next to the heater's own supply cable or a shorted input in the heater electronics are typical. Depending on the wiring, the heater may run without a request or not at all. Designs with integrated control, such as Hanon's patent US11628706B2, add their own overheat sensing so that an unintended run does not destroy the element. No manufacturer documents P2B74 publicly. CARB wants such outputs monitored for electrical faults. Internal module and over-temperature faults have their own codes, P2DA4 and P2DA6.
- What you may notice
- Coolant heater off, or running without request
- Higher 12 V or high-voltage battery drain when parked if the heater runs on
- Weak cabin heat in cold weather
- Likely causes
- LikelyCommand wire shorted to a 12 V circuit
- PossibleHarness crushed or melted near the heater supply cable
- PossibleHeater electronics input shorted to its supply
- RareOutput stage of the commanding module faulty
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €1,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.