What does it mean?
P1329 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Knock Sensor 3 Signal Low Input .
Symptoms
- Check engine light on, usually with a freeze frame recorded under load
- Reduced power because the module retards ignition timing as a safe default
- Higher fuel consumption and duller throttle response
- Audible pinging or a metallic rattle under hard acceleration or when climbing, since knock protection is degraded
- On some engines a lower boost ceiling or a slightly reduced rev limit
Likely causes
- Knock sensor 3 loose or under-torqued, or mounted on a dirty or painted block surface, so engine vibration is damped before it reaches the piezo element
- Open circuit or high resistance in the sensor signal wire between the sensor and the PCM (powertrain control module)
- Corroded, spread or moisture-contaminated terminals in the knock sensor connector
- Broken shield or missing shield ground, which lowers signal amplitude and lets noise swamp the reading
- Internally failed piezo element in knock sensor 3
- Harness damage from heat where these sensors sit under the intake manifold
- Rarely, a failed knock processing input inside the PCM
How to fix it
- Read the freeze frame to see load, rpm and coolant temperature when the fault set, then try to repeat those conditions
- Unplug the knock sensor 3 connector and inspect both halves for green corrosion, pushed-back terminals and oil or coolant intrusion
- Measure sensor resistance and check it against the value the manufacturer specifies for that sensor type
- Watch knock sensor activity and the knock retard counter in live data while lightly tapping the block near the sensor with a small wrench; no reaction points to the sensor or its wiring
- Check continuity and resistance of the signal wire back to the module pin, and confirm the shield ground is clean and tight
- Remove the sensor, clean the mounting face down to bare metal and retorque it to the specified value, since torque strongly affects output
- Replace knock sensor 3 if it fails the checks; suspect the module only after wiring and sensor test good