P246D

Reductant Heater Control Circuit High Bank 1

P246D is a generic OBD-II powertrain diagnostic trouble code: Reductant Heater Control Circuit High Bank 1. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P246D
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P246D means

P246D is stored when the ECM detects a higher-than-expected voltage or current condition in the control circuit for the DEF (diesel exhaust fluid) heater element on Bank 1. The reductant heater is used to thaw frozen DEF in cold ambient temperatures so the SCR system can begin dosing within a specified warm-up time required by emissions regulations.

A circuit-high fault typically indicates a short to voltage in the heater control wiring, a failed relay or driver circuit, or an internal ECM fault. In some architectures, the heater is controlled via a pulse-width modulated relay, and a circuit-high fault means the sensed feedback voltage is above the expected range during the off-state of the command.

When this fault is active, the DEF heater may be permanently energized or non-functional, depending on system architecture. In cold climates this can prevent SCR system operation and lead to NOx emission threshold violations and associated torque derates. Diagnosis should start with circuit voltage checks at the heater connector before condemning the heater element or ECM driver.

Common causes

Most-frequently reported root causes when P246D is logged.

  • 1
    Short to voltage in the DEF heater control wiring harness.
  • 2
    Failed or stuck-closed heater relay providing continuous power.
  • 3
    Faulty ECM or SCR module output driver for the heater circuit.
  • 4
    Corroded or contaminated connector causing elevated resistance and voltage offset.
  • 5
    Incorrect heater element resistance due to internal heater failure.
  • 6
    Wiring chafed against chassis ground or positive rail.

Symptoms drivers notice

MIL illuminated.
DEF heater may remain energized continuously.
SCR system may fail to activate in cold ambient temperatures.
Possible DEF system warning indicator on the instrument cluster.
No drivability impact in warm ambient conditions.

How to diagnose P246D

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all DTCs and freeze frame data.
  2. 2
    Inspect the DEF heater wiring harness and connector for chafing, corrosion, or signs of short to voltage.
  3. 3
    Measure voltage at the heater control circuit with the heater commanded off.
  4. 4
    Check the heater relay for stuck-closed condition by removing it and testing operation.
  5. 5
    Measure heater element resistance and compare to specification.
  6. 6
    Check ECM heater driver circuit output voltage with the circuit disconnected.
  7. 7
    Replace the relay or repair wiring if a short to voltage is confirmed.

Vehicles where we've handled P246D

Platforms in our catalogue with confirmed P246D coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Is P246D dangerous to ignore?

In warm climates the immediate impact is low, but in freezing temperatures the DEF heater is critical for SCR operation. Ignoring it can lead to DEF freezing, SCR system failure, and regulatory derate cycles.

What is the difference between circuit high and circuit low faults on the DEF heater?

Circuit high (P246D) means the ECM sees excess voltage in the circuit, suggesting a short to power or stuck relay. Circuit low means insufficient voltage, pointing to an open circuit or short to ground.

Can a stuck relay cause P246D?

Yes. A relay that remains closed when commanded open will keep the heater energized and present an elevated voltage to the ECM feedback circuit, triggering the circuit-high code.

Does this code affect DEF dosing?

Not directly, but if the heater is inoperative in cold weather, frozen DEF cannot be thawed in time, which prevents dosing and can trigger additional SCR faults.

Disabling P246D in software

RaceTune can permanently disable P246D — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P246D disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C50 verified 1 software version
  • Bosch EDC17CP09 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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