What it means
The control circuit of coolant heater A reports a control circuit/open condition. Auxiliary preheating of the coolant cannot be commanded as expected.
At a glance
- Usually lights the check-engine light
How it works
Coolant heater A uses an electrically controlled element to warm coolant before the engine produces much heat. The control module checks whether heater A's circuit responds when commanded; it sets P2B72 when the circuit appears open, so the heater may not operate.
Common causes
Most likely first.
- Open in heater control wire
- Open heater element
- Pin pushed back out of connector body
Symptoms
- Check-engine light
- Coolant or engine may take longer to warm up
- Cabin heat may take longer to become warm
How to diagnose it
- Check freeze-frame data and heater commands to confirm when the fault occurred and whether heater A was requested.
- With the system off and cool, inspect heater A's connector for a backed-out pin, corrosion, looseness, or damaged wiring.
- Check the heater A control wire for continuity between the specified terminals, following the manufacturer's wiring information.
- Test heater A's element for an open circuit using the manufacturer's procedure and specification.
- If the wiring, connector, and element pass, check the control module's output and circuit monitoring against the manufacturer's procedure.
Common fixes
- Reseat a pushed-back heater A connector pin and secure the connector.
- Repair an open or damaged heater A control wire.
- Clean or repair a poor heater A connector connection.
- Replace the heater A element if it tests open.
Can I keep driving?
The engine can generally be driven if its normal temperature stays stable, but heater A may not preheat the coolant, delaying engine warm-up and cabin heat. Avoid relying on quick cabin heat in cold weather, and stop if the engine overheats.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.