P2950

Reductant Heater Control Circuit

P2950 is a generic OBD-II powertrain diagnostic trouble code: Reductant Heater Control Circuit. 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
P2950
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2950 means

P2950 is set when the ECU detects an unexpected electrical condition on the reductant heater control circuit. The reductant heater is used to thaw frozen DEF in cold weather and to maintain optimum fluid temperature for dosing. The control module drives the heater element and monitors the circuit for current or voltage feedback consistent with normal operation.

When the observed circuit response falls outside the expected range, the fault is logged. This can occur due to an open circuit, short to ground, short to voltage, or a failed heater element. Without a functioning heater, the DEF system may be unable to operate in freezing conditions, resulting in SCR system unavailability and elevated NOx emissions when ambient temperatures are below the freezing point of DEF.

Because the heater fault may only manifest at low temperatures, technicians should note ambient conditions at fault capture time. Inspect the heater wiring and connector for corrosion or damage, as moisture exposure in the tank area is common and frequently the primary cause of this fault.

Common causes

Most-frequently reported root causes when P2950 is logged.

  • 1
    Open circuit in the reductant heater element supply or ground wiring.
  • 2
    Short to ground on the heater control wire causing a circuit fault signal.
  • 3
    Failed reductant heater element with broken resistance wire.
  • 4
    Corroded or damaged connector at the DEF tank heater or supply module.
  • 5
    Blown fuse or fusible link protecting the reductant heater circuit.
  • 6
    Faulty ECU or reductant module output driver for the heater channel.
  • 7
    Damaged wiring harness routed near heat sources or moving components.

Symptoms drivers notice

MIL illuminated with P2950 stored.
DEF system inoperable in cold weather due to inability to thaw frozen reductant.
SCR system fault warning or DEF temperature warning on the instrument cluster.
Possible secondary low-temperature or DEF quality faults when ambient is cold.
No observable symptom in warm climates where heater is not required for operation.

How to diagnose P2950

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze-frame data with a scan tool before clearing.
  2. 2
    Inspect the reductant heater fuse and replace if blown; investigate cause if a new fuse also blows.
  3. 3
    Inspect the heater connector and wiring harness for moisture intrusion, corrosion, or physical damage.
  4. 4
    Measure heater element resistance at the connector and compare to manufacturer specification.
  5. 5
    Check for supply voltage and proper ground at the heater connector with ignition on and heater commanded on.
  6. 6
    If element resistance and circuit voltages are correct, suspect the control module output driver.
  7. 7
    Repair wiring faults, replace the heater element, or replace the supply module as directed by test results.

Vehicles where we've handled P2950

Platforms in our catalogue with confirmed P2950 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can P2950 be ignored in warm climates?

In consistently warm climates the heater is rarely needed, but the fault should still be repaired because it indicates a wiring or component fault that could affect other reductant system functions.

Is the DEF tank heater a separate part or integrated?

On most vehicles the heater is integrated into the DEF tank or supply module assembly and may require replacing the module rather than just the element.

Will P2950 prevent the engine from starting?

Typically no, but in some vehicles with strict NOx inducement strategies, accumulated SCR faults can eventually lead to engine derate or start inhibit after a specified number of drive cycles.

Does P2950 affect DEF quality monitoring?

The heater fault itself does not directly affect DEF quality monitoring, but if the heater failure prevents dosing in cold conditions, NOx efficiency will drop and secondary SCR faults may be logged.

Disabling P2950 in software

RaceTune can permanently disable P2950 — 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 P2950 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 EDC17C56 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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