P0328
- Powertrain
- Generic (SAE)
- Emissions
Diagnose soon
The default case is an electrical fault costing power and fuel economy while knock protection is disabled — real but not urgent. The exception matters: if the sensor is reporting a true mechanical noise such as a rod knock, a loose flexplate, or sustained detonation, the underlying condition is serious and this code is an early warning rather than a nuisance. Listen to the engine before you decide which case you have.
- Safe to drive
- Safe if the engine sounds normal. If you hear knocking, pinging, or a deep rhythmic rap, stop driving and investigate.
Knock Sensor 1 Circuit High Input (Bank 1)
The bank 1 knock sensor signal is reading higher than the computer expects. That can mean an electrical fault in the circuit, or it can mean the sensor is faithfully reporting a genuine mechanical noise the engine should not be making.
P0328 sets when the knock circuit level exceeds the calibrated upper threshold. Two very different root causes produce the same code. Electrically, a signal line shorted to a voltage source or an internally failed sensor drives the input high. Mechanically, a real vibration source — a loose accessory, a rattling heat shield, a failing bearing, or actual detonation — produces excessive genuine sensor output. Distinguishing these two is the whole job, and getting it wrong is expensive in opposite directions.
How the car detected itThe module samples the knock circuit within a defined RPM and load window and compares the level against an upper limit. Levels sustained above that limit set the code. The PCM will typically fall back to a retarded ignition timing table because it can no longer separate real knock from whatever is elevating the signal.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Safe if the engine sounds normal. If you hear knocking, pinging, or a deep rhythmic rap, stop driving and investigate.
- Urgency
- Diagnose soon
- Will it pass emissions
- No
- If ignored
- In the electrical case, ongoing power and economy loss and a failed emissions inspection. In the mechanical case, ignoring it lets whatever is making the noise progress — a rattling heat shield is harmless, but a bearing knock or sustained detonation ends in major engine damage.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
- Power loss from defensive spark retard
- Increased fuel consumption
- Possible audible pinging under load
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Mechanical noise picked up by sensor (loose accessory) | Common | — |
| 2 | Signal wire shorted to supply voltage | Common | — |
| 3 | Sensor failed | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
How the engine actually sounds at idle and under load
This is the fork in the road. A deep rhythmic knock that rises with RPM, or a metallic pinging under acceleration, means the sensor may be correct and the engine is the problem.
The fuel octane in the tank and the octane the manufacturer requires
Fuel below the required octane in an engine that demands premium causes genuine detonation. It is the cheapest possible cause and it is often the answer.
Loose or rattling components near the sensor — heat shields, brackets, accessory pulleys, belt tensioner
The sensor cannot tell combustion knock from a rattling shield. Grabbing and shaking these takes a minute and resolves a real share of these codes.
The sensor mounting bolt torque and the harness for a short to voltage
A loose sensor rings against its boss and reads high. A signal wire chafed against an ignition or supply circuit does the same electrically.
Ignition timing retard on a scan tool
Shows whether the PCM is in its fallback strategy and whether retard tracks with load, which helps separate a constant electrical offset from load-dependent real knock.
Listen to the engine carefully before touching anything electrical
Tools Mechanic's stethoscope or a long screwdriver
Idle it, load it, and use a stethoscope on the block, the accessory drive, and the transmission bellhousing area. Separate a light metallic ping under acceleration from a deep rhythmic knock at idle from a rattle that changes with accessory load.
ExpectedA smooth engine with no rhythmic knock. Any distinct noise redirects the entire diagnosis toward mechanical causes.
Record freeze frame and correlate the code with driving conditions
Tools Scan tool
Check whether the code sets at light load or under heavy load and heat. Load-and-heat dependence suggests genuine detonation. Setting at idle with no load suggests an electrical fault or a mechanical rattle unrelated to combustion.
ExpectedA repeatable condition that tells you which branch to follow
Rule out fuel-related detonation
Tools Scan tool for coolant temperature, borescope if warranted
If the engine requires premium fuel, fill with the correct octane and drive a full tank. Check for carbon buildup, an over-advanced base timing setting on engines that allow adjustment, and a cooling system that runs hotter than it should, since all promote knock.
ExpectedKnock activity falls off with correct fuel and normal operating temperature
Physically check the sensor mounting and everything near it
Tools Torque wrench, hand tools, service data
Confirm the sensor bolt is at the manufacturer's torque, which is vehicle-specific. Then shake heat shields, brackets, the alternator, the belt tensioner, and the AC compressor for play. Remove or secure anything that rattles and retest.
ExpectedA properly torqued sensor and nothing loose within the immediate area
Inspect the harness for a short to voltage
Tools DMM, wiring diagram
With the sensor and the PCM connector disconnected, measure from the knock signal conductor to ground with the key on. Any voltage present means the conductor is contacting a powered circuit somewhere along its run.
ExpectedNo voltage on the disconnected signal conductor
Measure the sensor and verify circuit integrity
Tools DMM, service data, wiring diagram
Check sensor resistance against service data, check each conductor for continuity and resistance to the PCM, and confirm the shield is grounded at the single point the manufacturer specifies. Values are vehicle-specific. A dead short to the sensor body is a clear failure; an open or very high DC reading is normal on many two-wire piezo sensors and is not by itself a failure.
ExpectedResistance matching the manufacturer's specification where one is published, and clean, correctly shielded conductors. Where no resistance spec exists, judge the sensor functionally rather than on ohms.
Watch live knock data while tapping the block, then while raising accessory load
Tools Scan tool with knock PIDs, small metal tool
Tap near the sensor to confirm the circuit responds at all. Then turn on the AC, load the alternator, and steer to load the power steering pump, watching whether knock signal jumps. A signal that spikes with accessory load points at a mechanical noise source, not the sensor.
ExpectedResponse to tapping, and no dramatic jump when loading accessories
If genuine engine noise is present, diagnose it as an engine problem
Tools Oil pressure gauge, stethoscope, inspection tools
Check oil level, oil pressure, and oil condition. Investigate bearing noise, piston slap, a cracked flexplate, or a loose torque converter bolt. At this point the knock code is a symptom and the noise is the fault.
ExpectedOil pressure within the manufacturer's specification and no rhythmic mechanical noise
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Secure or replace a loose heat shield, bracket, or accessory component | The rattle is located by stethoscope or hand check and the knock signal drops after securing it | $60–$350 | DIY |
| Correct fuel octane and address conditions that promote detonation | Knock activity and timing retard fall off with the manufacturer-specified fuel and normal coolant temperature | $0–$200 | DIY |
| Repair a signal wire shorted to a voltage source | Voltage measured on the knock signal conductor with sensor and PCM disconnected | $90–$400 | DIY |
| Re-torque or reinstall the sensor on a cleaned mounting surface | Sensor found loose or seated on rust, debris, or an incorrect washer | $80–$500 | Hard |
| Replace the bank 1 knock sensor | Mechanical noise ruled out by stethoscope and load testing, fuel octane correct, mounting and torque verified, no short to voltage on the signal conductor, and the sensor still drives the circuit high or fails a manufacturer-specified resistance check | $150–$1,100 | Hard |
| Clean carbon deposits from combustion chambers on an engine with knock-promoting buildup | Borescope shows heavy deposits and knock is load- and heat-dependent with correct fuel | $300–$1,000 | Hard |
| Internal engine repair for a confirmed mechanical knock | Audible rhythmic knock located by stethoscope, supported by low oil pressure or metal in the oil | $2,000–$8,000 | Shop |
US independent-shop ranges, parts plus labour. The cheap outcomes on this code are genuinely cheap — a loose heat shield or the wrong fuel costs almost nothing. Sensor replacement cost is driven by access, and on many V6 and V8 engines the sensor sits under the intake manifold, which is several hours of labour plus gaskets. Budget about an hour of diagnostic labour to separate the electrical from the mechanical case before any part is bought — the two branches lead to repairs that differ by an order of magnitude.
- Replacing the knock sensor first. On a high-input code the sensor is the least likely of the three main causes.
- Condemning the sensor because it reads open on an ohmmeter. Many two-wire piezo sensors read effectively open at DC when healthy, so an open reading proves nothing on its own.
- Failing to listen to the engine, and replacing a sensor that was accurately reporting a genuine mechanical problem.
- Overlooking cheap fuel in an engine that requires premium.
- Skipping the rattling heat shield or loose accessory check because it seems too simple.
- Over-torquing the sensor on reinstallation in the belief that tighter reads better. Torque is a specification, not a preference, and it is vehicle-specific.
- Assuming bank 1 is a particular physical side of the engine instead of the bank containing cylinder 1.
- Knock Sensor
- Knock Sensor Wiring
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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