P2B67
NOx Sensor Circuit Low Voltage Bank 1 Sensor 2P2B67 is a generic OBD-II powertrain diagnostic trouble code: NOx Sensor Circuit Low Voltage 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 P2B67 means
P2B67 is stored when the aftertreatment or engine control module detects that the signal voltage from the downstream NOx sensor on Bank 1 (Sensor 2, located after the SCR catalyst) has fallen below the minimum calibrated threshold. The NOx sensor generates a signal that the module interprets as a proportional measure of NOx concentration in the post-catalyst exhaust gas. A voltage below the expected range during active sensor operation indicates an electrical fault in the sensor or its circuit.
A low voltage condition on the NOx sensor circuit commonly results from a short to ground in the signal wire, a failed sensor with an internally shorted sense cell, an open in the sensor heater circuit preventing the element from reaching operating temperature (which can suppress the signal), or a high-resistance fault in the reference or power supply lines to the sensor. The module monitors the output continuously and flags the fault when the measured signal is implausibly low given the current operating conditions.
With this fault active, the module cannot use the downstream NOx reading for SCR feedback control, which may cause the system to default to open-loop dosing. This increases the risk of over- or under-dosing reductant and reduces SCR catalyst conversion efficiency. The MIL is illuminated and a freeze-frame is recorded. Prompt diagnosis of the electrical circuit is recommended.
Common causes
Most-frequently reported root causes when P2B67 is logged.
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1
Short to ground on the NOx sensor signal wire.
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2
Failed NOx sensor with internally shorted sense cell.
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3
Open or high-resistance fault in the sensor heater supply circuit preventing warm-up.
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4
Damaged or corroded sensor harness connector causing signal line grounding.
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5
Chafed signal wire contacting the exhaust system or chassis ground.
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6
Failed sensor control unit (if the NOx sensor uses an integral controller module).
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7
Water or reductant ingress into the sensor connector.
Symptoms drivers notice
How to diagnose P2B67
A typical diagnostic flow when this code is present.
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1
Retrieve all DTCs and note any accompanying sensor heater circuit codes.
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2
With the ignition on and engine cold, check for battery voltage on the sensor heater supply circuit.
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3
Inspect the NOx sensor connector and wiring for damage, corrosion, or moisture intrusion.
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4
With the sensor connected, measure signal circuit voltage relative to ground; a reading shorted to ground confirms a wiring or sensor fault.
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5
Disconnect the sensor and recheck the signal wire voltage; if it rises to reference voltage, the sensor is internally shorted.
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6
If the signal wire is grounded with the sensor disconnected, trace the harness for a short to ground.
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7
Replace the defective sensor or repair wiring, clear codes, and verify signal plausibility during a drive cycle.
Related powertrain codes
Frequently asked questions
Can a failed sensor heater cause P2B67?
Yes. If the sensor element never reaches operating temperature due to a heater fault, the output signal will remain at an invalid low level, potentially triggering this code.
Is the downstream sensor (Sensor 2) more prone to failure than the upstream sensor?
The downstream sensor is exposed to post-SCR exhaust and reductant residues, which can cause contamination and accelerated wear over time.
Will this code clear itself if the sensor warms up?
If the cause is intermittent (e.g., a temperature-dependent short), the code may not be active when hot, but it will be stored as a pending or confirmed DTC.
How do I confirm the sensor is bad versus the wiring?
Disconnect the sensor and measure the signal circuit at the harness side. If voltage returns to expected reference level with the sensor disconnected, the sensor itself is the fault source.
Disabling P2B67 in software
RaceTune can permanently disable P2B67 — 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.
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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