P2340 — Cylinder 5 Above Knock Threshold

What does OBD2 code P2340 mean?

P2340 — Cylinder 5 Above Knock Threshold. A fault in the knock (detonation) detection. Short, gentle driving to a shop is usually possible. Typical causes: low-octane or contaminated fuel, engine carbon buildup causing real detonation, loose sensor mounting or incorrect torque.

What are the symptoms of P2340?

Drivers most often notice: Check Engine Light on, worse fuel economy, metallic pinging under acceleration, reduced power (ECM retards timing).

How much does it cost to fix P2340?

Repair sensor wiring — $80–$250; Decarbonization service — $150–$400; Replace the knock sensor — $150–$450. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will P2340 clear itself?

Sometimes P2340 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose P2340 myself?

Start with a scan: confirm P2340, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the knock (detonation) detection, and verify the suspect component against live data before buying parts.

What does P2340 mean?

Seeing P2340 on your scanner? The control unit has caught the knock (detonation) detection operating outside its calibrated window. The formal description is “Cylinder 5 Above Knock Threshold”, and the code is grouped under powertrain (engine/transmission) faults.

P2340 refers specifically to cylinder 5. On inline engines cylinders are counted from the front (belt end); on V-engines the numbering depends on the manufacturer, so check the firing-order diagram for your exact model. Location matters for the repair bill: some cylinders require intake manifold removal, which adds labor time.

To set P2340, the control module compares live readings of the knock (detonation) detection against calibrated limits, usually over several drive cycles. Alongside the code it stores a freeze frame — a snapshot of rpm, load, coolant temperature and vehicle speed at the moment of failure. Reading that snapshot first saves diagnostic time.

What causes P2340?

• engine carbon buildup causing real detonation
• failed knock sensor
• damaged knock sensor wiring or connector
• low-octane or contaminated fuel

Common symptoms of P2340

• Check Engine Light on
• worse fuel economy
• metallic pinging under acceleration
• reduced power (ECM retards timing)
• often no audible symptoms

How to diagnose P2340

1. Connect an OBD2 scanner, confirm P2340 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
3. Visually inspect the wiring harness and connectors related to the knock (detonation) detection for damage, corrosion, chafing or poor contact.
4. Inspect the knock sensor connector and wiring — heat and vibration damage them often.
5. Check sensor torque and mounting surface; an improperly seated sensor reads incorrectly.
6. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2340 does not return.

How to fix P2340

Start with the cheapest and most common causes before replacing expensive parts:

• Repair sensor wiring — $80–$250
• Decarbonization service — $150–$400
• Replace the knock sensor — $150–$450

How much does it cost to fix P2340?

Repair cost depends on which component actually failed. Typical scenarios for P2340 (parts and labor, USD, independent shop rates):

• Repair sensor wiring: $80–$250
• Decarbonization service: $150–$400
• Replace the knock sensor: $150–$450

Overall, fixing P2340 usually costs between $80 and $450. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P2340?

Drive gently and avoid hard acceleration. With knock detection off, the engine is not protected from detonation — sustained pinging under load can damage pistons and bearings over time.

Related OBD2 codes

• P2300: Ignition Coil "A" Primary Control Circuit Low
• P2301: Ignition Coil "A" Primary Control Circuit High
• P2302: Ignition Coil "A" Secondary Circuit
• P2303: Ignition Coil "B" Primary Control Circuit Low
• P2304: Ignition Coil "B" Primary Control Circuit High
• P2305: Ignition Coil "B" Secondary Circuit