Open circuit, damaged wire or high resistance in the heater control or supply wiring; Corroded, loose or pushed-out pins at the heater connector or relay connector; Blown fuse in the heater supply or control circuit; Faulty heater relay or power driver for heater B; Failed heater element with an internal open circuit; Faulty control unit output driver or an outdated calibration, where the manufacturer lists it as a known issue.

P01EC

Engine Coolant Heater B Control Circuit/Open.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
EC: FaultThe specific fault in that area

What it means

P01EC means the control unit has detected an open circuit, or a fault in the control circuit, for engine coolant heater B. This is an electric heater that warms the coolant, and it is normally switched by a relay or driver output. The code sets when the commanded state of the output does not match the voltage or current feedback, which points to a break in the circuit. The exact location and layout of heater B depend on the vehicle and engine.

Symptoms

Engine management warning light on
Slow engine warm-up in cold weather
Weak or slow cabin heating
Poor demisting or slow windscreen clearing
Higher fuel consumption or longer cold running on some models

Possible causes

Open circuit, damaged wire or high resistance in the heater control or supply wiringlikely
Corroded, loose or pushed-out pins at the heater connector or relay connectorlikely
Blown fuse in the heater supply or control circuitpossible
Faulty heater relay or power driver for heater Bpossible
Failed heater element with an internal open circuitpossible
Faulty control unit output driver or an outdated calibration, where the manufacturer lists it as a known issuerare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including coolant temperature and ambient temperature when the code set.
Check for related codes for heater A, the coolant temperature sensor, or supply voltage faults, and deal with those first.
Using the wiring diagram for the vehicle, find heater B, its relay and its fuse, then check the fuse and visually inspect the wiring, connectors and relay for damage, corrosion or water ingress.
Inspect the heater and relay connector pins for tension, corrosion and push-back, and repair as needed.
With the ignition on, check for the correct supply voltage and earth at the heater and relay, following the manufacturer's procedure.
Where the diagnostic equipment supports it, command heater B on and off and check that the relay clicks and the control signal changes at the connector.
Measure the control wire for continuity between the control unit and the relay or heater, and check for shorts to earth or supply.
Check the heater element resistance against the manufacturer's specification, and test the relay if it is a separate component.

How to fix

Repair or replace damaged wiring and restore good continuity in the control and supply circuits.
Clean, repair or replace faulty connectors and terminals.
Replace the blown fuse only after finding and correcting the cause of the failure.
Replace a faulty heater relay or driver module.
Replace the coolant heater if its element is open circuit, then refill and bleed the cooling system as the manufacturer specifies.
Where a manufacturer bulletin confirms a control unit fault or outdated calibration, repair or update the control unit as directed.

Can I keep driving?

Low severity

The car can normally be driven, but warm-up and cabin heat may be poor in cold weather. Book it in for diagnosis soon, and stop if other warnings appear or the engine shows signs of overheating.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.