P2343: Cylinder 8 Above Knock Threshold

What it means

Sustained knock above the threshold on cylinder 8 — typical on V8 engines under load with poor fuel.

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 8 to detect abnormal combustion. P2343 sets when the cylinder 8 knock indication remains above its threshold, and the module may retard ignition; sustained knock or a sensor or wiring fault can produce the condition.

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 check cylinder 8 knock and ignition correction readings to identify the load and temperature when the code set.
2. Listen for pinging under the same conditions and verify that the fuel is the grade specified for the vehicle.
3. Inspect knock-sensor wiring and connectors involved in cylinder 8's knock evaluation for damage, corrosion, moisture, or loose contacts.
4. Check cooling-system operation and signs of overheating that could promote knock under load.
5. If the sensor reading stays high without audible knock, test its circuit and investigate mechanical noise according to the manufacturer's procedures.

Common fixes

• Use the vehicle's specified fuel grade if the fuel is unsuitable.
• Repair damaged or corroded knock-sensor wiring and connectors.
• Correct cooling-system faults that lead to overheating.
• Address confirmed carbon deposits or mechanical noise; replace the sensor only if testing identifies it as faulty.

Can I keep driving?

Avoid heavy acceleration and sustained high load while cylinder 8 knock is detected, because the module may reduce power and persistent knock can damage the engine. Stop if the noise becomes severe or the engine overheats.