P0327
Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor)P0327 is a generic OBD-II powertrain diagnostic trouble code: Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor). 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 P0327 means
P0327 is stored when the PCM detects that the voltage signal from knock sensor 1 on bank 1 (or the single knock sensor) is consistently below the manufacturer's minimum acceptable threshold — typically below approximately 0.5 V DC on most resonant-type sensor systems. This is a circuit-level fault: the ECM sees a signal that is stuck low or absent rather than merely erratic (which would set P0326).
Knock sensors generate voltage by the piezoelectric effect: mechanical stress on the sensing element from engine block vibrations produces a proportional electrical signal. The PCM supplies a 5 V reference on some designs or simply monitors the AC signal returned from the sensor. When the signal stays at or near ground at all times, the PCM interprets this as a shorted signal wire, a failed sensor with no output, or an open circuit that allows the line to pull low.
A rail-low reading on the knock sensor circuit means the PCM loses the ability to detect detonation in real time. To protect the engine, the software typically defaults to a conservative, retarded ignition timing map. This noticeably reduces power output, particularly at higher engine loads, and worsens fuel consumption. The engine may also exhibit pinging or knocking sounds that would normally be suppressed by timing corrections — the sensor fault eliminates the feedback loop that prevents knock.
Common culprits are a failed knock sensor (internal short to ground), a chafed signal wire touching the chassis, a corroded or water-contaminated connector, or — on flat-response two-wire sensors common on Toyota and GM platforms — a broken ground path. P0327 will also appear if the sensor was replaced with an incompatible aftermarket unit whose resistance characteristics are outside the PCM's acceptance window.
Common causes
Most-frequently reported root causes when P0327 is logged.
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1
Failed knock sensor with internal short to ground
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2
Signal wire shorted to ground (chafed insulation, pinched harness)
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3
Corroded or water-contaminated sensor connector
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4
Broken or high-resistance sensor ground path (two-wire flat-response sensors)
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5
Oil or coolant leaked onto the sensor body or connector
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6
Incompatible aftermarket knock sensor with incorrect resistance characteristics
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7
Loose sensor mounting causing intermittent contact loss
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8
PCM input circuit fault (rare)
Symptoms drivers notice
How to diagnose P0327
A typical diagnostic flow when this code is present.
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1
Retrieve all codes and freeze-frame data with a scan tool; note engine RPM, load, and coolant temperature at the time of the fault
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2
Visually inspect the knock sensor, its mounting boss on the engine block, and the wiring harness — look for cracked insulation, oil saturation, corrosion, or loose connectors
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3
Unplug the sensor and measure resistance across the sensor terminals (typical flat-response/two-wire: 500–620 Ω; verify against OEM spec for your application)
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4
With the connector unplugged, check the signal wire to the PCM for a short to ground using a multimeter; resistance to chassis ground should be infinite
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5
Inspect the reference voltage or bias voltage at the PCM-side connector pin (varies by design; commonly 2.5 V or 5 V depending on sensor type)
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6
Use a graphing scan tool or lab-scope to monitor the live sensor output — tap the engine block near the sensor and confirm voltage spikes are generated
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7
Verify correct OEM-specified sensor is installed; check aftermarket sensor resistance against factory specification
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8
Repair wiring faults and re-test; if wiring is good and sensor fails resistance test, replace the knock sensor
Related powertrain codes
Frequently asked questions
Will P0327 cause the engine to knock?
It can — indirectly. Because the PCM loses its knock feedback, it cannot retard timing when detonation occurs. Genuine engine knock may go uncorrected, accelerating wear on pistons, rod bearings, and cylinder walls. Addressing the code promptly avoids potentially expensive internal damage.
Is P0327 expensive to repair?
Usually not. The knock sensor itself is often a modest-cost part. The bulk of repair cost comes from labour to access the sensor, which is deeply buried on some engines (notably certain GM 3.6L V6 and Toyota 4-cylinder designs). Wiring repairs, if needed, vary in complexity.
Can I clear P0327 and just drive on?
Clearing the code without repair is not advisable. The code will return within one or two drive cycles, and during the intervening period the engine runs on protective retarded timing with no active knock detection. The underlying fault — typically a shorted wire or failed sensor — must be corrected.
Does P0327 have any effect on turbo or supercharged engines?
Yes, and the risk is higher. Forced-induction engines are more prone to knock due to elevated cylinder pressures. The loss of active knock correction when P0327 is set means the engine is running with less safety margin against detonation, making prompt diagnosis especially important.
Disabling P0327 in software
RaceTune can permanently disable P0327 — 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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