P2340: Cylinder 5 Above Knock Threshold

What it means

The knock-sensor evaluation reports cylinder 5 above the knock threshold over a sustained window. The ECU retards ignition for that cylinder; persistent knock indicates poor fuel quality, carbon deposits or cooling issues.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control module evaluates knock-sensor vibrations associated with cylinder 5 to detect abnormal combustion. P2340 sets when the cylinder 5 knock indication stays above its threshold, prompting the module to reduce ignition advance; persistent knock or a biased sensor signal can trigger it.

Common causes

Most likely first.

1. Abnormal combustion knock
2. Knock sensor or wiring fault

Symptoms

• Check-engine light
• Pinging or rattling under acceleration
• Reduced power or sluggish acceleration

How to diagnose it

1. Record freeze-frame data and review cylinder 5 knock and ignition correction data to see whether the fault appeared under load, at a particular engine temperature, or at idle.
2. Listen for pinging under the conditions in the freeze frame, and check for poor fuel quality or an incorrect fuel grade.
3. Inspect the knock sensor wiring and connectors serving cylinder 5's knock evaluation for damage, corrosion, moisture, or loose connections.
4. Check engine cooling operation and look for signs of overheating or deposits that could create a cylinder 5 hot spot.
5. If the knock signal remains high without audible knock, test the sensor circuit and investigate mechanical noise using the manufacturer's procedures.

Common fixes

• Use fuel of the grade specified for the vehicle if unsuitable fuel is the cause.
• Repair damaged or moisture-contaminated knock-sensor wiring or connectors.
• Correct a cooling-system problem causing excessive engine temperature.
• Address confirmed carbon deposits or mechanical noise, and replace the sensor only if its circuit tests indicate failure.

Can I keep driving?

Avoid hard acceleration and sustained high load while cylinder 5 knock is reported, since the module may reduce power and persistent abnormal combustion can cause engine damage. Stop if the rattling becomes severe or the engine overheats.