P0327
- Powertrain
- Generic (SAE)
- Emissions
Diagnose soon
Nothing fails immediately. On most vehicles the PCM falls back to a retarded timing table so the engine is not leaning on a sensor it cannot trust; other strategies simply disable knock control and continue on the base timing table, which leaves the engine with no detonation protection at all. Either way the cost is real: reduced power, worse fuel economy, and degraded or absent knock protection. The risk becomes meaningful if you tow, run low-octane fuel, or work the engine hard in heat, because unheard detonation under load is genuinely damaging.
- Safe to drive
- Safe for normal, light driving. Avoid towing, heavy loads, and low-octane fuel until repaired — knock protection is degraded, and on some strategies it is switched off entirely.
Knock Sensor 1 Circuit Low Input (Bank 1)
The signal from the bank 1 knock sensor is reading lower than the computer expects, so the engine computer stops trusting knock detection. On most vehicles it also pulls ignition timing back as a precaution, which costs you power and fuel economy; some strategies simply disable knock control instead, which means no protection and no warning.
A knock sensor is a piezoelectric element that converts block vibration into a small AC voltage. The PCM monitors that circuit for an expected electrical characteristic — typically a bias voltage or a background signal level consistent with a running engine. P0327 sets when the measured level sits below the low threshold, indicating an element that has lost output, a signal line shorted to ground, or an open that collapses the circuit to the low rail. Bank 1 is the bank containing cylinder 1, and which physical side of the engine that is varies by manufacturer.
How the car detected itThe module samples the knock circuit in a defined RPM and load window where combustion noise should be present, then compares the measured signal or bias level against a calibrated low limit. Sustained readings below that limit set the code. Because the check needs the engine running in a specific window, this code often will not set at idle and may take a drive cycle to appear or to confirm as repaired.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Safe for normal, light driving. Avoid towing, heavy loads, and low-octane fuel until repaired — knock protection is degraded, and on some strategies it is switched off entirely.
- Urgency
- Diagnose soon
- Will it pass emissions
- No
- If ignored
- You keep paying in fuel economy and lost power indefinitely, and the vehicle will fail an emissions inspection in areas that check readiness and stored codes. Light use is usually uneventful on vehicles whose fallback retards timing, but not every strategy does — if yours does not, the engine is running unprotected. Under sustained heavy load with poor fuel, unprotected detonation can damage pistons and bearings.
- 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 | Knock sensor failed | Very common | — |
| 2 | Signal wire shorted to ground | Common | — |
| 3 | Connector pins corroded - high contact resistance | 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.
The sensor connector and the short harness pigtail at the sensor
Knock sensors live in hot, dirty places on the block. Corroded terminals and heat-hardened, cracked pigtail insulation are the most common failure on this circuit and are visible.
Harness routing for chafe against the block, brackets, or the intake
A signal wire rubbed through to bare metal against the block is a direct short to ground, which produces exactly a low-input reading.
Whether the sensor mounting bolt is tight and the mating surface is clean
A knock sensor only reads correctly when clamped flat against clean metal. A loose sensor or debris under it reduces output and can read as low input.
Ignition timing retard values on a scan tool
Shows whether the PCM is in a retarding fallback strategy at all, and if it is, quantifies what the fault is costing and gives a clear before-and-after check after repair.
Whether a second knock sensor code is also stored
Two sensors failing at once is unlikely. A shared ground, shared shield, or common connector fault is far more likely and changes where you look.
Record freeze frame and confirm the code is current, not history
Tools Scan tool
Note RPM, load, and coolant temperature at set time. Clear the code and drive the vehicle in a load range that puts the engine in the monitor's test window to see whether it returns.
ExpectedThe code returns under load if the fault is present
Inspect the sensor, its pigtail, connector, and harness routing
Tools Inspection light, mirror or borescope, scan tool
Follow the wiring from the sensor to wherever it joins the main harness. Look for chafe points, melted insulation near exhaust components, oil-soaked terminals, and green corrosion. Wiggle the harness while watching live knock data.
ExpectedIntact insulation, clean terminals, and no data change during the wiggle test
Measure the sensor's resistance with it disconnected, and interpret it against the sensor type
Tools DMM, service data
Measure across the sensor terminals, and from each terminal to the sensor body. Compare against the manufacturer's specification — the correct value depends on whether the sensor is a resonant or broadband type and whether an internal resistor is present, so it is vehicle-specific. A dead short to the sensor body is a clear failure. An open or very high reading is not a failure on many designs, because a piezoelectric element is a capacitive source and reads effectively open at DC unless the sensor contains an internal resistor.
ExpectedA reading that matches the manufacturer's specification for this sensor type. A dead short to the sensor body is a clear failure. An open or very high reading is NOT proof of failure — many two-wire piezo sensors are effectively open at DC by design. If service data gives no resistance spec, do not condemn the sensor on ohms; confirm it functionally with the tap test and, where the design allows, by scoping or AC-volts-testing its output while tapping the block.
Test the harness for a short to ground with the sensor disconnected
Tools DMM, wiring diagram
With both the sensor and the PCM connector disconnected, measure from the signal conductor to chassis ground. This is the test that separates a bad sensor from a bad wire, and it is the step most often skipped.
ExpectedVery high resistance to ground. A low reading confirms a shorted harness, not a bad sensor.
Verify circuit continuity and shield grounding end to end
Tools DMM, wiring diagram
Check each conductor from sensor connector to PCM connector for continuity and for excessive resistance. Many knock circuits are shielded; confirm the shield is grounded at the single point the manufacturer specifies, since a shield grounded at both ends or not at all corrupts a very small signal.
ExpectedLow resistance on each conductor and a correctly terminated shield
Tap-test the block near the sensor while watching live data
Tools Small metal tool, scan tool with knock PIDs, oscilloscope or DMM on AC volts
With the engine idling, tap the block near the sensor with a small wrench and watch the knock signal or knock retard PID respond. A working sensor and circuit will react. Where access allows, scope the sensor output or read it on AC volts while tapping — that separates a dead element from a circuit or PCM problem. This is a functional test of the whole path, not just the parts, and on sensors with no published resistance spec it is the test that decides.
ExpectedA visible change in the knock signal or knock retard value, or measurable AC output at the sensor, when tapping. No response with wiring proven good points at the sensor, or at the PCM input if the sensor itself produces output.
Verify the sensor is installed and torqued correctly if it has been serviced before
Tools Torque wrench, wire brush, service data
Remove the sensor, clean the mounting boss to bare metal, remove any thread sealant or washer that does not belong, and reinstall to the manufacturer's torque. Torque value is vehicle-specific and it matters — both under- and over-torque change sensor response.
ExpectedSensor seated flat on clean metal at the specified torque
Consider the PCM only after sensor, wiring, and shield are proven
Tools DMM, oscilloscope, wiring diagram
A known-good sensor, verified wiring, correct shield grounding, and no response to the tap test point at the PCM's knock input. Confirm PCM power and grounds before condemning it.
ExpectedEverything upstream verified good and the fault still present
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Replace the bank 1 knock sensor | Harness proven good (no short to ground, continuity and shield verified), and the sensor produces no response to a tap test at the block with a scope or knock PID monitored — or resistance is shorted, or outside a manufacturer-specified value where one exists | $150–$1,100 | Hard |
| Repair a signal wire shorted to ground or a chafed harness section | Low resistance from the signal conductor to ground with the sensor and PCM disconnected | $90–$400 | DIY |
| Repair or replace corroded connector terminals or the sensor pigtail | Visible corrosion or damaged insulation, or knock data changes during a wiggle test | $80–$300 | DIY |
| Correct shield grounding or repair a poor engine ground | Shield measures open or grounded at the wrong point, and correcting it restores normal signal | $90–$300 | DIY |
| Reinstall the existing sensor correctly on a cleaned mounting boss at specified torque | Sensor found loose, seated on rust or debris, or previously installed with sealant or an extra washer | $80–$500 | Hard |
| Replace the engine control module | Known-good sensor, verified wiring and shield, no response to tap test, and PCM power and grounds confirmed good | $600–$1,900 | Shop |
US independent-shop ranges, parts plus labour. The spread on sensor replacement is enormous because access is everything. On engines where the sensor sits on the outside of the block it is a short job. On many V6 and V8 engines the sensors live under the intake manifold, which means removing the manifold, replacing gaskets, and several hours of labour for a part that costs well under a hundred dollars.
- Replacing the knock sensor without testing the harness for a short to ground, which is the other main cause of a low-input reading.
- Condemning a knock sensor because it reads open on an ohmmeter. Many two-wire piezo sensors have no internal resistor and read effectively open at DC when perfectly healthy — on those, only a functional test tells you anything.
- Installing the new sensor with thread sealant, an added washer, or the wrong torque, which changes how vibration couples into it and can set the code again immediately.
- Not cleaning rust and scale off the mounting boss before installing the new sensor.
- Assuming bank 1 is the side of the engine nearest the front or nearest the driver. Bank 1 is the bank containing cylinder 1, and that varies by manufacturer.
- Clearing the code, seeing it not return within a few minutes, and declaring it fixed. The knock monitor runs in a specific load window and needs a proper drive cycle.
- Blaming reduced power on a fuel or transmission problem when the PCM's own timing retard fallback is the entire cause.
- 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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