What does it mean?
Heater element A of the electric coolant heater is switched by an output in the control module, and that output is monitored for a plausible voltage and current. This code is stored when the monitored control line sits at a low voltage, or draws more current than the driver allows, at a moment when it should not. In practice the circuit is grounded somewhere it should not be: a chafed wire touching the engine or the body, an element that has shorted internally, or a driver stage that has failed short. The module disables the heater output to protect itself, so the heater stops working as soon as the code sets. Since this is a high-current load, a short here often blows the circuit fuse repeatedly as well.
Symptoms
- MIL (check engine lamp) on and the coolant heater no longer working at all.
- Poor cabin heat and long warm-up times whenever the ambient temperature is low.
- Fuse for the heater circuit blowing repeatedly after replacement.
- Slow demisting and a cold cabin on short winter journeys.
- Slightly increased fuel consumption while the engine remains in its warm-up strategy.
Likely causes
- Control wire for heater A chafed through and shorted to ground against the engine, a bracket or the body panel.
- Heater element A shorted internally, drawing far more current than intended.
- Coolant or water in the heater connector bridging the control terminal to ground.
- Harness damage after previous work, with a wire trapped under a fastener or pierced by a cable tie.
- Failed driver stage inside the control module that stays switched on regardless of the command.
- Relay with welded contacts holding the circuit closed when it should be open.
How to fix it
- Read the freeze frame and note whether the code sets only when the heater is commanded on.
- Disconnect the heater element and the module connector, then check for continuity between the control terminal and ground; continuity with both ends disconnected means the harness is shorted.
- If the harness is clean, measure the resistance of element A; a value far below specification indicates an internally shorted element.
- Inspect the harness along its whole route for chafing, particularly where it crosses brackets and hot components, and check the connector for coolant intrusion.
- Test the relay for welded contacts where the circuit is relay-switched.
- Repair the short or renew the element, fit a new fuse and confirm with the scan tool that the output now switches cleanly and the current draw is normal.
- Replace the control module only after both the wiring and the load have been proved good.