P0327

What does P0327 mean?

P0327 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor).

This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.

Symptoms commonly associated with this code

Symptoms that drivers often report alongside this code. Not all may apply to every case:

• • Engine warning light on, sometimes with no other obvious change to how the car drives
• • Noticeable drop in power, especially pulling up a hill or overtaking on the motorway
• • A metallic pinging or knocking under load when you put your foot down
• • Slightly worse fuel economy as the ECU runs more cautious timing
• • Hesitation or a flat spot when accelerating from low revs
• • On plenty of cars, the only thing you'll notice is the dash light

Possible causes

Causes commonly associated with P0327, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.

1. 1. Knock sensor worn out or failed internally, the usual suspect on higher-mileage cars where it's been heat-cycled for years
2. 2. Corroded or broken wiring in the sensor circuit, very common on older VAG petrols and BMW straight-sixes where the loom runs hot near the block
3. 3. Poor connector contact, the pins go green or the connector works loose with engine vibration
4. 4. Bad earth on the sensor circuit, which drags the signal voltage down and trips a low-input code
5. 5. Sensor not torqued correctly to the block, these need a specific clamp load to read properly and a loose one reports rubbish
6. 6. Weak charging system pulling overall voltage down, less common but it can skew the reading
7. 7. ECM internal fault or out-of-date software, rare, and only worth considering once everything else checks out

How mechanics typically diagnose

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.

1. 1. Scan it and read the freeze-frame data, then check for any other codes sitting alongside it. A misfire or fuel trim code stored at the same time changes the picture.
2. 2. Get eyes on the sensor and its wiring. Knock sensors live in a filthy part of the engine, so look for green corrosion in the connector, chafed insulation, and a connector that isn't fully seated.
3. 3. Check the sensor is torqued down properly to the block. These are fussy about clamp load, and a sensor that's been disturbed or wasn't done up right will read low even if it's a good unit.
4. 4. Backprobe the connector and measure the sensor's AC output, you should see roughly 0.5 to 2.0 volts as the engine runs. Sitting under 0.2 volts points at a dead sensor.
5. 5. Test continuity and resistance back to the ECM and confirm the earth is solid, you want well under 0.5 ohms on the ground side. A poor earth is a classic cause of a low-input code with a perfectly good sensor.
6. 6. Check battery and alternator voltage at idle, 13.5 to 14.5 volts is what you're after. Low system voltage can drag the signal down and send you chasing a sensor that's fine.

Common questions about P0327