P2C66

NOx Sensor Heater Control Circuit Bank 2 Sensor 2

P2C66 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Heater Control Circuit Bank 2 Sensor 2. 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
P2C66
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P2C66 means

P2C66 is set when the control module detects a fault in the heater control circuit of the downstream NOx sensor located on Bank 2 (Sensor 2). NOx sensors require internal heating to reach and maintain operating temperature before accurate gas concentration measurements can be made. The module commands the heater via a dedicated control circuit and monitors heater current or voltage feedback to verify correct operation.

A fault in this circuit can mean the heater is not receiving power, the heater ground is open, the heater element has failed internally, or the module's heater driver is damaged. When the heater cannot maintain the sensor at operating temperature, the NOx sensor measurement becomes unreliable or unavailable, and the SCR closed-loop control strategy is degraded or switched to open-loop operation.

While a heater circuit fault does not immediately disable the vehicle, it prevents proper NOx monitoring and can mask deteriorating SCR efficiency. Extended operation with an unheated or improperly heated NOx sensor can also expose the sensing element to thermal shock from uncontrolled temperature swings, potentially accelerating sensor failure. The fault is typically stored after the module confirms heater current is outside expected limits for a defined period at startup.

Common causes

Most-frequently reported root causes when P2C66 is logged.

  • 1
    Failed NOx sensor heater element with open internal resistance.
  • 2
    Open or broken wire in the sensor heater supply or ground circuit.
  • 3
    Corroded or damaged heater circuit terminals in the NOx sensor connector.
  • 4
    Blown fuse protecting the NOx sensor heater power supply circuit.
  • 5
    Faulty heater driver circuit within the NOx sensor control module.
  • 6
    Chafed wiring causing an intermittent open on the heater control line.

Symptoms drivers notice

MIL illuminated; NOx monitoring system flagged as degraded.
Delayed or absent NOx sensor readiness after cold start.
SCR dosing operating in open-loop mode due to unreliable NOx feedback.
No noticeable driveability impact in most cases.
Possible additional downstream NOx sensor signal or efficiency codes if heater failure is prolonged.

How to diagnose P2C66

A typical diagnostic flow when this code is present.

  1. 1
    Read all DTCs and freeze-frame data before beginning any component testing.
  2. 2
    Check the fuse supplying the NOx sensor heater circuit and replace if blown, then investigate the cause of the blown fuse.
  3. 3
    Inspect the NOx sensor connector and heater circuit wiring for open circuits, corrosion, or damage.
  4. 4
    Measure heater element resistance at the sensor connector and compare to specification.
  5. 5
    Verify heater supply voltage reaches the sensor connector with the circuit powered.
  6. 6
    Check heater ground circuit continuity from the sensor back to the chassis ground point.
  7. 7
    If wiring and power supply are confirmed good, replace the NOx sensor and retest.

Vehicles where we've handled P2C66

Platforms in our catalogue with confirmed P2C66 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Does P2C66 mean the NOx sensor itself needs replacement?

Not necessarily. A blown fuse or broken wire can cause P2C66 without the sensor being faulty. Always check the circuit before replacing the sensor.

Can I drive with P2C66 active?

Yes, the vehicle typically remains driveable, but NOx monitoring is degraded. Repair within a reasonable timeframe to maintain SCR system accuracy and avoid additional faults.

How does the module know the heater is not working?

The module monitors the heater circuit for expected current draw when the heater is commanded on. An open circuit draws no current, triggering the fault.

Is Bank 2 Sensor 2 before or after the SCR catalyst?

Sensor 2 is typically the downstream sensor, located after the SCR catalyst on Bank 2, used for post-SCR NOx efficiency monitoring.

Disabling P2C66 in software

RaceTune can permanently disable P2C66 — 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 P2C66 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

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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