P0333
Knock Sensor 2 Circuit High Input (Bank 2)P0333 is a generic OBD-II powertrain diagnostic trouble code: Knock Sensor 2 Circuit High Input (Bank 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 P0333 means
P0333 is set when the ECM detects an abnormally high voltage on the Knock Sensor 2 signal circuit for Bank 2 — typically a reading at or near battery voltage or the ECM reference voltage when a low quiescent voltage is expected. A stuck-high condition is usually caused by a short to the voltage supply rail in the signal wire, a severely degraded sensor shorted internally, or electrical interference coupling voltage into the circuit.
The knock sensor is a passive device that normally rests near 0 V in quiescent state and oscillates slightly during engine vibration. A persistently elevated voltage prevents the ECM from reading meaningful knock data from Bank 2. As with all knock sensor circuit faults, the ECM responds with a fixed conservative timing retard, sacrificing power and efficiency to protect the engine. P0333 must be differentiated from P0331 (signal exists but is implausible) and P0332 (signal stuck low) through targeted circuit testing. Loose sensor mounting, which can generate vibration artifacts and skew readings, should also be checked.
Common causes
Most-frequently reported root causes when P0333 is logged.
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1
Short to voltage supply on the knock sensor 2 signal wire
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2
Damaged knock sensor connector with signal pin contacting battery or switched power
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3
Failed knock sensor 2 with internal short to supply
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4
Knock sensor 2 mounting loose, allowing excessive vibration that drives signal out of range
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5
Electrical interference from adjacent components (ignition wires, alternator) coupling voltage into the circuit
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6
Low fuel pressure or incorrect fuel octane causing knock events that push signal amplitude above expected range
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7
Faulty PCM/ECM reference or input circuit (diagnose last)
Symptoms drivers notice
How to diagnose P0333
A typical diagnostic flow when this code is present.
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1
If audible engine knock is present, address the mechanical cause first before diagnosing the sensor circuit
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2
Verify fuel octane meets manufacturer specification, as low-octane fuel causes knock events that can drive the sensor signal high
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3
With the ignition on and sensor disconnected, measure voltage on the signal wire at the harness connector — should be approximately 5 V reference, not battery voltage; if battery voltage is present, a short to power exists in the harness
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4
Measure resistance between the signal wire and all power supply wires with everything disconnected to identify a chafe-induced short
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5
With the sensor reconnected, measure resistance across the KS2 terminals and compare to spec; an internal short may read near 0 Ω
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6
Check the sensor mounting torque — a loose sensor can generate excessive vibration artifacts; retorque to specification and retest
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7
Inspect wiring routing near ignition coil wires or alternator leads and add separation or shielding if interference is suspected
Related powertrain codes
Frequently asked questions
What voltage should the knock sensor 2 signal read normally?
At rest (engine off, ignition on) the signal line typically sits at the ECM reference voltage of approximately 5 V. With the engine running, a flat-response piezo sensor produces an oscillating signal around that reference proportional to block vibration — amplitude stays within a narrow band under normal conditions. A sustained reading near battery voltage (12–14 V) indicates a short to power.
Can P0333 be caused by aftermarket parts?
Yes. Aftermarket ignition leads routed too close to the knock sensor harness can inject high-frequency voltage spikes into the signal circuit. Aftermarket engine components that alter vibration characteristics can also push the sensor output outside the ECM's expected window. Check routing and shielding if recently modified.
Could P0333 result from an engine mechanical problem?
Yes, indirectly. Severe detonation, worn bearings, or piston slap can generate vibration amplitudes that drive the sensor signal beyond its normal operating range. If the sensor and wiring test normal, a compression or cylinder leakdown test on Bank 2 is warranted.
How do I distinguish P0333 from P0331?
P0331 is a rationality fault — the sensor is electrically present but its response pattern is implausible during actual or induced knock events. P0333 is a hard electrical fault — the circuit voltage is persistently above the expected range. Circuit voltage measurement with a DVOM differentiates them quickly.
Disabling P0333 in software
RaceTune can permanently disable P0333 — 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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