What does it mean?
P1321 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Knock Sensor 3 Circuit Low Input .
Symptoms
- MIL (check engine lamp) on
- Ignition timing retarded as a safety measure, giving a clear loss of power
- Higher fuel consumption and duller throttle response
- Real detonation may go undetected, so pinging can be heard under load
- Sluggish performance on hills and when towing
Likely causes
- Signal wire shorted to ground or broken
- Knock sensor with a shorted internal element
- Sensor mounting bolt loose or torqued incorrectly, which kills the signal these sensors depend on
- Corroded connector or a damaged shielded lead, usually routed under the intake manifold
- Harness chafed where it passes between the block and the manifold
- Coolant or oil leaking into the sensor recess
How to fix it
- Read the knock sensor live values and see whether the channel reacts when the block is tapped lightly near the sensor
- Inspect the connector and the shielded lead for corrosion, chafing and broken shielding
- Measure the sensor's resistance and compare with specification
- With the sensor unplugged, check the signal wire for a short to ground
- Confirm the mounting bolt is clean, dry and torqued exactly to specification, since even a washer or thread sealant changes the reading
- Replace the sensor if it is out of specification, or repair the shorted harness section
- Clear the codes and confirm normal timing advance and no knock retard on a road test