OBD-II trouble code
P0327: Knock Sensor 1 Circuit Low (Bank 1 or Single Sensor)
The knock sensor on bank 1 is reporting signal voltage below the PCM's minimum threshold — meaning the PCM is no longer hearing the engine. Without a working knock sensor, ignition timing defaults to a safer, more conservative map and the engine loses both power and efficiency.
Quick facts
- System
- Powertrain
- Category
- Knock & Other
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $800
- DIY difficulty
- Intermediate DIY
Browse every code in P0300–P0394, or start from the full code library.
What does P0327 mean?
A knock sensor is a piezo accelerometer bolted to the engine block. It listens for the very specific frequency of detonation — the sound of combustion happening too early, before the piston has reached the right position. When the PCM hears knock, it retards ignition timing to protect the engine. When the knock sensor stops sending a signal, the PCM has no way to detect detonation, so it falls back to a conservative timing map that assumes the engine might be knocking even when it isn't.
P0327 sets when the knock sensor signal voltage drops below the minimum threshold for the diagnostic time window — usually because the sensor itself has failed internally, the wiring has opened up, or the connector has corroded. The piezo crystal inside knock sensors degrades with age and heat exposure, and they are treated as a wear item on higher-mileage engines.
One pattern is documented well enough to be worth naming: older GM Vortec/LS-family trucks and SUVs, broadly the 1999-2007 4.8L, 5.3L and 6.0L engines. On these the knock sensors sit under the intake manifold in cylinder valley wells that fill with debris and moisture over time. The classic failure mode is a corroded sensor, sometimes with water actually pooled in the well. Chevy Silverado, Tahoe, Suburban, and GMC Sierra owners know this code well. The repair is straightforward but labor-intensive because the intake manifold has to come off.
The other common cause is a damaged wiring harness. Knock sensor wires run through the valley or along the block in hot areas, and chafing or melted insulation creates intermittent or hard opens. Subaru EJ-series knock sensor wiring and Nissan VQ-series connectors both come up often in this role, but inspect your own harness rather than assuming the reported pattern applies to your car.
Drivability symptoms are usually subtle. The engine still runs because knock sensing isn't load-bearing — it's a protection layer. What you lose is the smart ignition advance the engine would normally make under good conditions. Power drops slightly, fuel economy drops a couple MPG, and on platforms where the knock sensor is also a feedback for spark advance under acceleration, you may feel reduced throttle response.
Common causes
- Failed knock sensor — piezo element degraded internally (the dominant cause on aged engines)
- Corroded knock sensor on GM LS trucks where the sensor sits under the intake manifold in a moisture-prone well
- Open or shorted knock sensor wiring — chafe damage in the valley or along the block
- Failed knock sensor connector with corroded pins
- Loose knock sensor — torque spec matters because the sensor relies on mechanical coupling to the block
- Aftermarket knock sensor of incorrect specification
- PCM signal-input fault (rare)
- Aftermarket performance tune that has disabled or modified knock sensor diagnostics improperly
Symptoms
- Check Engine Light on
- Mild loss of power, particularly under acceleration
- Reduced fuel economy
- Slightly delayed throttle response
- Possible pinging or knocking under heavy load if real detonation is occurring undetected
- Engine sounds normal in most cases
Diagnostic steps
- 1.Pull all codes. P0327 alone is the classic sensor failure case. P0327 with P0328 may point at shared wiring or PCM-side issues.
- 2.On GM LS trucks, plan for the intake manifold to come off — the sensor sits in a well under the intake. Check for water pooled in the wells before assuming a bad sensor.
- 3.Disconnect the connector and measure resistance across the sensor terminals, but know what the number can and cannot tell you. Specs vary enormously by sensor type — some read in the hundreds of thousands of ohms to several megohms, others are effectively open to a meter by design — so look up your platform's figure rather than judging against a general range. A dead short is a clear fault. An in-spec reading exonerates nothing: a piezo element fails by losing output, not by changing resistance, so a sensor that measures perfectly can still be deaf.
- 4.Do the tap test, which is the check that actually reads output. Switch the meter to AC millivolts across the sensor terminals with the connector off, then tap the block near the sensor with a small metal tool. A live sensor produces a brief AC output; a flat response on a sensor that passed the resistance check is the real evidence it has failed. Many handheld meters sample too slowly to catch it reliably, so treat a flat reading on a cheap meter as inconclusive and confirm with a scope or with the scan tool's knock-sensor PID while the engine runs.
- 5.If the sensor responds and the code persists, back-probe the signal wire at the PCM connector to check for harness continuity.
- 6.Inspect the connector for green corrosion, oil contamination, or pushed-back pins.
- 7.On Subaru EJ engines, inspect the wiring at the standard chafe points along the manifold.
- 8.When replacing the sensor, torque it to spec — too loose and it won't read engine vibration correctly, too tight and the piezo crystal can crack.
- 9.After replacement, clear the code, drive through a heavy-load condition (highway on-ramp acceleration is ideal), and confirm the code stays off.
Repair cost
$150 – $800
Knock sensor part itself is $30-150 depending on platform. On engines where the sensor is accessible (most Subaru, Nissan VQ, some Honda V6), total replacement is $150-300. On GM LS trucks where the sensor sits under the intake manifold, expect $500-800 because the intake has to be removed — and most owners replace both sensors at the same time since labor dominates. Wiring repair is $100-400 depending on access. The 'do them both at once' rule applies on V-engines where access is labor-intensive — you don't want to redo this job in six months.
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Related repairs
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.