P2338 — Cylinder 3 Above Knock Threshold

P2338 — Cylinder 3 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, damaged knock sensor wiring or connector, engine carbon buildup causing real detonation.

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution 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.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P2338 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs 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.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the knock (detonation) detection for damage, corrosion, chafing or poor contact.
Subsystem check Inspect the knock sensor connector and wiring — heat and vibration damage them often.
Subsystem check Check sensor torque and mounting surface; an improperly seated sensor reads incorrectly.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2338 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P2338 (parts and labor, USD, independent shop rates): Decarbonization service: $150–$400; Repair sensor wiring: $80–$250; Replace the knock sensor: $150–$450. Overall, fixing P2338 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.

Common questions

What are the symptoms of P2338?

Drivers most often notice: reduced power (ECM retards timing), often no audible symptoms, worse fuel economy, Check Engine Light on.

What does OBD2 code P2338 mean?

Is it safe to drive with P2338?

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.

What is the most common cause of P2338?

The most common causes are: low-octane or contaminated fuel, damaged knock sensor wiring or connector, engine carbon buildup causing real detonation.

Will P2338 clear itself?

Sometimes P2338 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.

What does P2338 mean?

The engine control module sets P2338 when it detects a fault in the knock (detonation) detection. In practical terms: cylinder 3 above knock threshold. The code belongs to the powertrain (engine/transmission) group of OBD2 codes.

P2338 refers specifically to cylinder 3. 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 P2338, 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 P2338?

damaged knock sensor wiring or connector
low-octane or contaminated fuel
engine carbon buildup causing real detonation
failed knock sensor
loose sensor mounting or incorrect torque

Common symptoms of P2338

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

How to diagnose P2338

Connect an OBD2 scanner, confirm P2338 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
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.
Visually inspect the wiring harness and connectors related to the knock (detonation) detection for damage, corrosion, chafing or poor contact.
Inspect the knock sensor connector and wiring — heat and vibration damage them often.
Check sensor torque and mounting surface; an improperly seated sensor reads incorrectly.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2338 does not return.

How to fix P2338

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

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

How much does it cost to fix P2338?

Repair cost depends on which component actually failed. Typical scenarios for P2338 (parts and labor, USD, independent shop rates):

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

Overall, fixing P2338 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 P2338?