P01E9Engine Coolant Heater A Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Engine coolant heater A is an electric coolant heater switched by the engine module, directly or via a relay or power stage, to shorten warm-up – less cold-start emissions and faster cabin heat; A and B denote two separately switched heaters or stages. It is not the same as a mains-powered block heater (which the vehicle does not control) or the electrically heated thermostat (P0597–P0599). CARB requires output components to be checked for correct response or at least for circuit faults. This code reports a control circuit voltage that is too low – typically a short to ground in the control line or the heater/relay. No manufacturer using these codes was found in the GM, Ford or NHTSA documents checked; the typical driver diagnosis (open circuit detected with the driver switched off, as GM does for other outputs) is an analogy, and thresholds are unknown.
- What you may notice
- Check engine light on
- Longer warm-up, cabin heat slower in winter
- Usually no change in driving
- Likely causes
- LikelyControl wire shorted to ground (chafed harness)
- PossibleHeater element or relay coil shorted to ground
- PossibleMoisture or corrosion in the connector
- RareControl module output stage
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.