P20BE: Reductant Heater B Control Circuit Performance
What to do
Ask for the connectors and the shared supply to be checked before any heated line is ordered. These assemblies are expensive, and if several heater faults are stored at once the cause is usually one shared connection rather than several failed heaters.
Ask which part this heater serves on your vehicle, since the lettering differs between manufacturers and the cost varies a lot.
Get it done before deep winter. In mild weather you will notice nothing — the fault only matters once the fluid can actually freeze, and by then the vehicle has begun counting down towards not restarting.
Be aware the heated line is often a single sealed part, so a failed element can mean the whole line.
What this code means
The second reductant heater circuit is being commanded but not performing as expected.
Heater B is most often the supply line — the hose carrying fluid from the tank to the metering unit — though the lettering varies by manufacturer and should be confirmed rather than assumed.
A line heater has a harder job than the tank heater and fails more often, which is worth knowing. The tank holds a large volume in an insulated container; a line is a thin hose running the length of the underbody, exposed to airflow, road spray and freezing wind. It loses heat continuously while it works.
Its construction follows from that. The heating element is resistive wire wound along the hose and moulded into the assembly — which is why a failed line heater usually means replacing the entire heated line rather than an element. Those assemblies are surprisingly expensive, so it is worth confirming the diagnosis before ordering.
The diagnostic order that saves money here: connector, then temperature sensor, then the line. Corrosion under the vehicle is commoner than element failure, and a misreporting sensor produces this code with a working heater.
Reading the whole heater set together helps. Several heater codes at once point at a shared supply, earth or module output rather than several failed elements — the same pattern the glow plug family shows, for the same reason.
Likely causes
Start here
- Faulty reductant line heater · moderate
- Corroded or loose connector · easy
- Faulty reductant temperature sensor · moderate
Less common
- High resistance in sensor wiring · moderate
- Water ingress into connector · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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