P27C0
NOx Sensor Heater Control Circuit (Bank 1 Sensor 2)P27C0 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Heater Control Circuit (Bank 1 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.
What P27C0 means
P27C0 is set when the ECM or SCR module detects a fault in the heater control circuit of the NOx sensor on Bank 1, downstream position (Sensor 2). NOx sensors incorporate an internal ceramic heater element that must rapidly bring the sensor to its operating temperature, typically above 600 degrees Celsius, before accurate NOx measurement is possible. The heater circuit is independently monitored and controlled by the module.
A fault in the heater control circuit can present as an open, short to ground, or short to voltage on the heater supply or control wire, or as an internal failure of the heater element itself. When the heater cannot bring the sensor to temperature, the NOx cell remains inactive and the module receives no valid signal, causing it to disable or degrade SCR system operation. Cold climate starts are particularly vulnerable to this fault because the heater must work against low ambient temperatures.
Diagnosis should begin with measuring heater circuit resistance at the sensor and verifying supply voltage and ground integrity. Compare measured heater resistance against the manufacturer specification for this sensor type. If the heater element is open, the sensor must be replaced. If wiring is the issue, repair the harness before condemning the sensor.
Common causes
Most-frequently reported root causes when P27C0 is logged.
-
1
Open circuit in the NOx sensor heater supply or return wire.
-
2
Failed NOx sensor heater element with broken resistance wire.
-
3
Short to ground on the heater control circuit.
-
4
Short to voltage on the heater circuit causing overload and driver fault.
-
5
Corroded or damaged sensor connector increasing heater circuit resistance.
-
6
Failed heater driver stage in the ECM or SCR module.
-
7
Thermal damage to the heater wiring harness routed near exhaust components.
Symptoms drivers notice
How to diagnose P27C0
A typical diagnostic flow when this code is present.
-
1
Use a scan tool to capture all DTCs and freeze frame data, noting any companion NOx signal or SCR codes.
-
2
Measure heater element resistance at the sensor connector with the sensor cool; compare to manufacturer specification.
-
3
Inspect the sensor connector and harness for heat damage, chafing, or corrosion.
-
4
Verify heater supply voltage at the sensor connector with the ignition on.
-
5
Check heater ground circuit continuity from the sensor back to the module or chassis ground.
-
6
If the heater element resistance is out of specification or open, replace the NOx sensor.
-
7
If wiring is the fault, repair the harness, clear codes, and retest over a cold-start drive cycle.
Vehicles where we've handled P27C0
Platforms in our catalogue with confirmed P27C0 coverage.
Related powertrain codes
- P2700 — Friction Element A Apply Time Range/Performance
- P2701 — Friction Element B Apply Time Range/Performance
- P2703 — Friction Element D Apply Time Range/Performance
- P2704 — Friction ElementEApply Time Range/Performance
- P2705 — Friction ElementFApply Time Range/Performance
- P2706 — Solenoid F Malfunction
Frequently asked questions
Will the NOx sensor give any readings with a bad heater?
Possibly, once exhaust temperatures are high enough to heat the sensor passively. However, readings early in the drive cycle will be invalid, and the system will continue to flag the heater fault.
Is P27C0 the same as a wideband O2 sensor heater code?
They are conceptually similar (both monitor an internal heater for an electrochemical sensor) but refer to different sensor types. A NOx sensor is more complex than a wideband O2 sensor and the two are not interchangeable.
Can I clean the NOx sensor heater circuit or is replacement always needed?
If the heater element itself is open, the sensor must be replaced. If the issue is a corroded connector or damaged wire, repairing the harness is sufficient and sensor replacement is not necessary.
How long does it take to confirm the repair worked?
The heater is evaluated during the first cold-start warm-up sequence. A single cold-start drive cycle where the sensor heats normally and no code returns is typically sufficient to confirm the repair.
Disabling P27C0 in software
RaceTune can permanently disable P27C0 — 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.
ECUs with a P27C0 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.
Got P27C0 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file