OBD-II trouble code
P0329: Knock Sensor 1 Circuit Intermittent (Bank 1 or Single Sensor)
The bank 1 knock sensor signal drops out or goes erratic intermittently rather than failing outright. The engine keeps running, but the PCM pulls ignition timing as a precaution, costing a little power and fuel economy.
Quick facts
- System
- Powertrain
- Category
- Knock & Other
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $400 – $600
- DIY difficulty
- Intermediate DIY
Browse every code in P0300–P0394, or start from the full code library.
What does P0329 mean?
The knock sensor is a piezoelectric microphone bolted to the engine block. It listens for the sharp, high-frequency rattle of detonation — fuel igniting spontaneously ahead of the spark rather than burning smoothly. When the powertrain control module (PCM) hears that signature in the sensor's output, it retards ignition timing on the affected cylinders until the knock stops. That closed-loop protection is what lets modern engines run aggressive timing for power and efficiency without destroying pistons on a tank of marginal fuel.
P0329 is the intermittent member of the knock sensor 1 family. Where P0325 covers a general circuit fault, P0327 covers a signal that is persistently too low, and P0328 covers a signal that is persistently too high, P0329 says the circuit was working, then briefly wasn't. The PCM captured a momentary dropout, a spike, or an implausible burst of signal, logged it, and the reading returned to normal. On a bank-1 designation, that means the sensor on the side of the engine containing cylinder 1 — or, on an inline-four or other single-sensor engine, simply the only knock sensor fitted.
Because the fault comes and goes, the causes skew toward connection quality and mechanical mounting rather than a dead sensor element. A corroded or partially seated connector, spread terminal pins, and chafed shielded wiring are the leading offenders. Knock sensor circuits are particularly sensitive because the signal they carry is a low-level AC voltage — often well under one volt in normal operation — so even modest resistance, moisture, or electrical noise on the circuit can corrupt it. A knock sensor that is not torqued correctly is another classic cause: these sensors work by mechanical coupling to the block, and a loose sensor, or one over-torqued past spec, produces an inconsistent signal that the PCM can't interpret. On GM LS-family engines, the knock sensors sit in wells under the intake manifold that are prone to collecting water, which corrodes the connectors and produces exactly this intermittent pattern.
Driveability effects are mild but real. Whenever the PCM decides the knock circuit is untrustworthy, it defaults to a conservative timing table, which typically costs a modest amount of power and a mile or two per gallon. Most drivers describe it as the car feeling slightly flat rather than broken. The genuine long-term risk is that real detonation goes undetected — under towing loads, on mountain grades, in hot weather, or on low-octane fuel — and sustained knock damages pistons, rings, and bearings. It is not an emergency, but it is not something to ignore for a year either.
Common causes
- Corroded, moisture-intruded, or partially seated knock sensor connector
- Spread or backed-out terminal pins losing contact under vibration or heat
- Chafed or damaged knock sensor wiring, particularly where the shielded lead routes past brackets
- Knock sensor not torqued to specification — too loose or too tight both degrade mechanical coupling
- Water pooling in the under-intake sensor wells on GM LS-family V8 engines, corroding the connector
- Knock sensor element degrading internally and glitching before it fails outright
- Electrical noise from a failing alternator, ignition components, or aftermarket wiring bleeding onto the low-level signal circuit
- Poor ground or shield connection on the sensor circuit
Symptoms
- Check engine light on, sometimes coming and going across drive cycles
- Mild loss of power, most noticeable under load or on grades
- Fuel economy may drop while the module holds a conservative spark map. There is no published miles-per-gallon figure.
- Slightly softer or delayed throttle response
- Engine may sound and feel completely normal much of the time
- Audible pinging or rattle under heavy load if real detonation is going undetected
- Symptoms that appear only when fully warmed up or only over rough pavement
Diagnostic steps
- 1.Scan and record all codes with freeze-frame data. Note engine temperature, load, and speed at the moment of the fault — intermittent codes are found by reproducing those conditions.
- 2.Identify the bank 1 knock sensor location for your specific engine before starting. Bank 1 contains cylinder 1; on many V6 and V8 engines the sensor is under or behind the intake manifold.
- 3.Inspect the connector under good light for corrosion, moisture, green film, and pins that have backed out of the housing. Tension-test each terminal gently.
- 4.On the engines named in GM bulletin 02-06-04-023, look for water in the rear knock-sensor well. That bulletin's code is P0332, and its repair is the rear sensor at 20 Nm with an RTV dam left open at the rear. It is not a ranking of causes for this intermittent bank-1 code.
- 5.Wiggle-test the harness and connector with the engine idling while watching knock retard or knock sensor activity in live data. A jump when you move a specific section localizes the fault.
- 6.Measure resistance against the published figure for this part. Do not use a kilohm-to-megohm band. Some procedures treat a very high reading as correct. A reading inside the spec does not clear the sensor, because a piezo element fails by losing output. Follow with AC millivolts and a tap on the block at the temperature in the freeze frame. A slow meter can miss the pulse, so a flat trace is inconclusive.
- 7.Check continuity of the signal lead back to the PCM and confirm the shield or ground connection is clean and tight.
- 8.Verify the sensor mounting torque against specification. A knock sensor relies on mechanical contact with the block, and incorrect torque in either direction produces an unreliable signal.
- 9.If the wiring, connector, ground, and torque all check out and the glitch still appears in live data, replace the sensor and confirm the code stays away through a heavy-load drive cycle.
Repair cost
$400 – $600
Parts plus labor. RepairPal's national average for a knock sensor replacement is about $417–$589, rounded to $400–$600. A connector repair can sit under that and is not given a separate invented band. Replacing both sensors is the bulletin's instruction only where that bulletin says so. Bulletin 02-06-04-023 replaces the rear sensor.
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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.