P0327: Knock Sensor 1 Circuit Low (Bank 1 or Single Sensor)
Key takeaways
- P0327 means the signal from knock sensor 1, on bank 1 or the only knock sensor, is below what the engine computer expects.
- It is usually safe to drive, but the computer pulls ignition timing as a precaution, so expect a little less power and fuel economy.
- An open or damaged wire, a corroded connector or a loose sensor is often the cause before the sensor itself.
- An accessible sensor typically costs $150 to $400 installed; a sensor under the intake manifold on many V6 and V8 engines runs about $400 to $900.
- Subaru and Ford bulletins name P0327: Subaru changed the knock sensor design for durability, and Ford found a wire chafe near the knock sensor connector on some Explorers.
What P0327 means
The sensor that listens for engine knock on bank 1 is sending a signal that’s too weak to trust. Scanners call it Knock Sensor 1 Circuit Low (Bank 1 or Single Sensor); newer tools may say “Knock/Combustion Vibration Sensor 1 Circuit Low.” A knock sensor bolts to the engine block and turns vibration from early detonation (knock or ping) into a small voltage. The computer watches that signal and pulls ignition timing back when it sees knock. When the signal stays below the expected range, which is what an open wire, a bad connection or a dead sensor looks like, it sets P0327.
Sensor 1 is on bank 1, the side of a V6 or V8 with cylinder 1, or it’s the only knock sensor on engines that have one.
Is it safe to drive?
Yes, in most cases, and gently. Without a trustworthy knock signal, the computer runs conservative, retarded ignition timing, so the engine stays protected but feels a little slower and uses more fuel. Use the octane your owner’s manual specifies and skip towing and long full-throttle climbs until it’s fixed.
What changes the answer: audible pinging or knocking when you accelerate, or a flashing check engine light. Pinging with a dead knock sensor means the engine may be knocking with nothing correcting it, so ease off and get it checked soon. See can I drive with the check engine light on.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Open, chafed or rodent-chewed wiring, or a corroded connector | Inspect the harness and plug; check continuity and resistance back to the computer | $100–$250 |
| Sensor loose or not torqued to spec after earlier work | Check the mounting bolt; a loose sensor reads weak | Covered by diagnosis, or $100–$250 |
| Failed knock sensor, easy to reach (most four-cylinders) | Sensor resistance or output out of spec with good wiring | $150–$400 |
| Failed knock sensor under the intake manifold (many V6 and V8 engines) | Same tests, done at the connector; the sensor itself needs the intake removed | $400–$900 |
| Engine software needing an update | A bulletin covers your make, model and year | $100–$200, or free under warranty |
What to check first
- Read the other codes. P0327 with P0332, the bank 2 low code, points to shared wiring, a shared ground or connector, not two failed sensors at once.
- Inspect the connector and harness. Oil, coolant leaking from the intake and rodents all damage knock sensor wiring. Found at the harness, it may be a $100–$250 job.
- Check the sensor is tight. If anyone has had the intake off or replaced the sensor recently, a loose or wrongly torqued sensor is a strong suspect.
- Ask for a bulletin check. Subaru issued bulletins on 2011–2017 models announcing a redesigned, more durable knock sensor, listing P0327 among the codes it can set. Ford traced P0327 on 2016–2017 Explorer 3.5L EcoBoost engines built on or before Sept. 30, 2016, to a wire chafe near the knock sensor connector, and has other P0327 bulletins for the 2016 Explorer 3.5L and the 2012–2014 Focus 2.0L whose summaries don’t describe the fix.
- Test the sensor at the connector before anyone pulls the intake. If the sensor is buried, ask whether replacing both sensors and the harness while it’s open makes sense.
- Clear it and drive after a wiring repair; a low-circuit fault usually resets within a drive or two if it isn’t fixed.
Only 4 complaints filed with NHTSA mention P0327, spread over 3 models, so the bulletins are the better guide here.
What it costs
The cheap outcome is a wiring or connector repair, or tightening a loose sensor, at $100–$250. The common outcome on an engine with an accessible sensor is a new knock sensor at $150–$400. The expensive outcome is a sensor under the intake manifold on a V6 or V8 at about $400–$900, almost all of it labor. Paying for an hour of diagnosis first, usually $100–$180, saves money, because testing at the connector tells you whether the intake needs to come off at all.
Related codes
P0327 is one of the knock sensor 1 family: P0325 (circuit), P0326 (range or performance) and P0328 (circuit high). On V engines it can show up with the bank 2 codes P0330 and P0332. For how to pull and read the codes yourself, see how to read check engine light codes.
What owners report to NHTSA
4 complaints filed with NHTSA mention P0327, 4 of them since 2015, across 3 different models. The component owners most often filed it under: engine.
Manufacturer service bulletins that name P0327
6 technical service bulletins and manufacturer communications filed with NHTSA mention P0327, from 2 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- SUBARU FORESTER (2014, 2015, 2016, 2017), bulletin 10140468: 2.0L Turbor Models only. This Service Information Bulletin announces design changes to the engine?s knock sensor which will help improve vehicle assembly line efficiency and increase durability. In some cases, the Check …
- SUBARU B9 TRIBECA (2012, 2013, 2014, 2015), bulletin 10153187: This Service Information Bulletin announces design changes to the engine?s knock sensor which will help improve vehicle assembly line efficiency and increase durability. In some cases, the Check Engine light may illumina…
- FORD EXPLORER (2016, 2017), bulletin 10153933: Some 2016-2017 Explorer/Police Interceptor Utility vehicles equipped with a 3.5L EcoBoost engine built on or before 30-Sep-2016 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (D…
- FORD FOCUS (2012, 2013, 2014), bulletin 10136582: Some 2012-2014 Focus vehicles equipped with a 2.0L gasoline direct injection (GDI) engine may exhibit concerns of engine runs rough, crank no-start, loss of power, loss of engine RPM, and/or illuminated MIL with diagnost…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can I drive with P0327?
Usually, yes. The computer can't trust the knock signal, so it retards ignition timing to stay safe, and you lose a little power and mileage. Use the fuel grade your owner's manual calls for, avoid heavy towing and full-throttle runs, and get it checked if you hear pinging under load.
What is the difference between P0325 and P0327?
P0325 is a general fault in the knock sensor 1 circuit. P0327 is more specific: the signal is too low, which usually points to an open wire, a poor connection, a loose sensor or a sensor that has stopped producing much output.
Can a loose knock sensor cause P0327?
Yes. A knock sensor hears vibration through its mounting, so if it isn't tight against the block or was torqued wrong after earlier work, its signal can drop low enough to set the code. Checking the mounting is part of a proper diagnosis.
Should I replace both knock sensors?
If both are under the intake manifold, many shops recommend it, because the labor to reach them is the same and the other sensor is often just as old. If only one is accessible, replace the one the tests point to.