Cylinder 4 Above Knock Threshold
The knock sensor for cylinder 4 is detecting excessive detonation (engine knock) or has failed electrically. The PCM monitors knock sensor voltage to detect pre-ignition and adjust timing accordingly; when voltage exceeds normal thresholds on the cylinder 4 circuit, this code sets.
What You Might Notice
- Engine knocking or pinging noise under acceleration
- Reduced engine power and performance
- Decreased fuel economy
- Rough idle or hesitation during acceleration
- Check Engine Light illumination
Most Common Causes
- 1
Failed or faulty knock sensor
The knock sensor for cylinder 4 may have electrical degradation or internal failure, causing it to send abnormal voltage signals to the PCM.
- 2
Wiring or connector issues
Corroded, damaged, or loose wiring and connectors on the cylinder 4 knock sensor circuit can cause erratic voltage readings.
- 3
Actual engine detonation
Using fuel with octane rating too low, carbon buildup in the combustion chamber, or excessively advanced ignition timing can cause genuine knocking that triggers the sensor.
- 4
PCM or knock sensor control circuit fault
Internal PCM issues or problems with the knock sensor amplifier circuit can cause false knock detection signals.
How to Diagnose It
- 1
Check Failed or faulty knock sensor — The knock sensor for cylinder 4 may have electrical degradation or internal failure, causing it to send abnormal voltage signals to the PCM.
- 2
Check Wiring or connector issues — Corroded, damaged, or loose wiring and connectors on the cylinder 4 knock sensor circuit can cause erratic voltage readings.
- 3
Check Actual engine detonation — Using fuel with octane rating too low, carbon buildup in the combustion chamber, or excessively advanced ignition timing can cause genuine knocking that triggers the sensor.
- 4
Check PCM or knock sensor control circuit fault — Internal PCM issues or problems with the knock sensor amplifier circuit can cause false knock detection signals.
How to Fix It
- 1
Replace knock sensor for cylinder 4
Remove the faulty knock sensor from cylinder 4 and install a new OEM or quality replacement. Reconnect wiring and clear the code after installation.
- 2
Inspect and repair wiring and connectors
Check the knock sensor wiring harness and connector for corrosion, damage, or loose connections. Clean or replace connectors as needed and ensure secure mating.
- 3
Use higher octane fuel
If detonation is actual rather than sensor fault, switch to fuel with higher octane rating (premium grade) to prevent knock and allow the sensor to normalize.
- 4
Diagnose PCM and knock control circuit
If sensor and wiring check out, have a technician test the PCM knock sensor input circuit using a scope or dedicated diagnostic equipment to rule out control module failure.
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