P2338 – Cylinder 3 Above Knock Threshold

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: General | Location: Cylinder 3

Definition source: SAE J2012/J2012DA (industry standard)

DTC Structure (SAE J2012)

• P = Powertrain
• 2 = ISO/SAE Controlled
• 338 = Specific fault index for this code
• Fault type = General

3-byte note: Some platforms may report a 3-byte DTC with an added Failure Type Byte (FTB) suffix like -1A. Treat the base code and the FTB as separate: the base code identifies the subsystem; the FTB refines the failure subtype.

P2338 is a powertrain diagnostic trouble code indicating the control module has detected combustion knock on cylinder 3 exceeding the calibrated threshold. This code does not, by itself, prove a specific part has failed or that engine damage is occurring; it only confirms the monitored knock event crossed a limit during the conditions in which the monitor runs. The exact enabling criteria, detection logic, and how the vehicle reports related data (such as knock activity or misfire counts) can vary by vehicle, so always verify test procedures and specifications using the appropriate service information.

What Does P2338 Mean?

P2338 means Cylinder 3 Above Knock Threshold. In practical diagnostic terms, the powertrain control module determined that knock intensity attributed to cylinder 3 exceeded an allowed threshold while the knock monitoring strategy was active. SAE J2012 defines how DTCs are structured and named, but the threshold values, filters, and conditions used to assign knock to a specific cylinder vary by vehicle. Treat the code as an indicator of detected knock behavior on cylinder 3 and confirm the root cause through scan data review, mechanical checks, and verification testing.

Quick Reference

• System: Powertrain
• Official meaning: Cylinder 3 Above Knock Threshold
• Standard: ISO/SAE controlled
• Fault type: Plausibility
• Severity: MIL illumination is possible; sustained knock can lead to reduced performance and potential engine damage if the underlying cause is not corrected.

Symptoms

• MIL/Check engine light: Illumination may occur, sometimes after the condition repeats.
• Audible knock/ping: Rattling or pinging noises may be noticeable under load or acceleration.
• Reduced power: Engine may feel sluggish if spark timing is being pulled to control knock.
• Roughness: Vibration, rough running, or intermittent stumble may be present in certain RPM/load ranges.
• Poor fuel economy: Increased consumption can occur if timing and combustion efficiency are reduced.
• Hesitation: A brief lag during tip-in or climbing grades may be felt.

Common Causes

• Poor fuel quality or incorrect octane: Fuel that promotes knock can push cylinder 3 above the knock threshold, depending on operating conditions.
• Ignition timing control issues: Incorrect timing due to control strategy, incorrect learned values, or related sensor input errors can contribute to knock detection.
• Knock sensor signal concerns: A biased, noisy, loose-mounted, or otherwise unreliable knock sensor signal can lead to knock being interpreted as excessive on cylinder 3 (varies by vehicle design).
• Wiring/connector faults: Intermittent opens, shorts, corrosion, water intrusion, poor pin fit, or harness chafing affecting knock-sensing circuits or related inputs (as equipped).
• Ignition system faults on cylinder 3: Spark plug wear, incorrect plug type/gap, coil output issues, or secondary ignition leakage that can increase combustion irregularities.
• Fuel delivery issues affecting cylinder 3: Injector restriction, uneven fueling, low fuel pressure/volume, or control problems that create a lean condition under load.
• Unmetered air/vacuum leaks: Intake leaks that bias fueling, especially under certain loads, increasing tendency to knock.
• Engine mechanical contributors: Carbon buildup, abnormal compression, cooling system performance issues, or localized hot spots that can increase knock tendency (requires confirmation testing).

Diagnosis Steps

Tools commonly needed include a scan tool with live-data logging and freeze-frame access, a digital multimeter, basic hand tools for connector/harness inspection, and service information for the vehicle. Depending on design, you may also need equipment for fuel pressure/volume checks and ignition testing. Use manufacturer procedures for pinouts, torque specifications, and any cylinder-specific knock monitoring routines.

1. Confirm the DTC and capture data: Verify P2338 is present. Record freeze-frame data and any related DTCs (misfire, fuel trim, knock sensor, cooling, or fuel system codes). Clear codes only after saving this information.
2. Check for service updates and calibration notes: Using service information, confirm whether there are known updates for knock-related diagnostics or powertrain calibration that could affect detection logic (varies by vehicle).
3. Road-test with controlled logging: If safe, perform a short drive while logging key PIDs (engine load, RPM, spark advance/retard, knock-related data as available, fuel trims, coolant temperature). Try to reproduce conditions shown in freeze-frame without extended heavy load.
4. Quick visual inspection: Inspect ignition components and connectors relevant to cylinder 3 where accessible. Look for damaged insulation, oil intrusion, loose connectors, poor grounds, and intake ducting issues. Correct obvious problems before deeper testing.
5. Wiggle test for intermittents: With the engine idling (or key-on as appropriate), gently wiggle the harnesses and connectors associated with knock sensing and relevant engine sensors. Watch live data for dropouts/spikes and monitor for code resetting conditions.
6. Verify engine operating conditions: Confirm coolant level and that the engine reaches and maintains normal operating temperature. Overheating or abnormal temperature behavior can increase knock tendency and should be addressed before continuing.
7. Ignition system checks focused on cylinder 3: Inspect the cylinder 3 spark plug condition and correct type. Check for signs of detonation-related damage, fouling, or incorrect gap. If applicable, swap the ignition coil (or coil-on-plug unit) with another cylinder and see whether related symptoms or misfire data follows.
8. Fuel and air delivery checks: Evaluate fuel trims at idle and under load (as supported). If trims or drive symptoms suggest fueling problems, perform fuel pressure/volume testing per service info and check for injector balance/contribution issues (method varies by vehicle).
9. Knock sensor and circuit integrity testing: Using service information, identify the knock sensor circuit(s) and perform connector checks for corrosion/loose pins. Measure continuity and check for shorts to power/ground as directed. Perform voltage-drop testing on relevant grounds during engine operation to identify hidden resistance.
10. Mechanical and combustion contributors: If electrical, ignition, and fueling checks pass, perform mechanical verification as appropriate (compression/leak-down, intake leak test, and inspection for deposits or cooling system faults). Only proceed based on symptoms and service guidance.
11. Confirm the repair: After corrections, clear codes and repeat the drive cycle that originally set P2338. Review logged data to ensure knock-related parameters and spark control behavior are stable and the DTC does not return.

Professional tip: Treat P2338 as an “excess knock detected on cylinder 3” event, not a guaranteed mechanical failure. Use freeze-frame to recreate the exact load/RPM/temperature window, then compare ignition timing behavior, fuel trim response, and knock-related data across similar conditions. If your platform supports per-cylinder knock or misfire counters, use them to avoid replacing parts based on assumptions.

Possible Fixes

• Repair wiring/connectors: Fix damaged insulation, loose terminals, corrosion, or poor pin fit affecting the knock sensor circuit or related engine harness paths, then re-secure routing to prevent reoccurrence.
• Restore power/ground integrity: Clean and tighten ground points, correct high-resistance splices, and address any power feed issues found during voltage-drop testing that can distort sensor signals.
• Replace the knock sensor (if confirmed faulty): Only after testing shows the sensor for the affected bank/cylinder grouping is out of specification or unresponsive compared with known-good behavior.
• Correct mechanical contributors (if verified): Address confirmed sources of true knock on cylinder 3 such as ignition/fuel delivery faults, incorrect plug/coil operation, or air/fuel imbalance identified by misfire and fuel-trim diagnostics.
• Update/control-module correction (if applicable): If service information indicates a calibration update or known strategy issue affecting knock detection, apply the approved update after confirming all electrical checks pass.
• PCM/ECM replacement (rare): Consider only if all inputs, wiring, and sensor behavior are proven good and service information supports module fault as a remaining cause.

Can I Still Drive With P2338?

Driving with P2338 may be possible for short distances, but it is not recommended to continue operating the vehicle hard (heavy load, high RPM, towing) because knock control may be actively limiting performance or may not be able to protect the engine if knock is real. If you notice reduced power, severe vibration, misfire, unusual engine noise, overheating, or the vehicle enters a protective/limp mode, stop driving and have it diagnosed. If stalling, no-start, or any brake/steering warning occurs, do not drive.

What Happens If You Ignore P2338?

Ignoring P2338 can lead to persistent drivability issues such as power reduction, poor fuel economy, and intermittent misfire-like behavior, depending on how the control module responds to detected knock events. If the underlying issue is true cylinder knock, extended operation can increase the chance of internal engine damage over time. If the cause is electrical (wiring/connector/sensor signal integrity), the vehicle may continue to set the code and may apply conservative spark control, increasing emissions and potentially triggering additional related faults.

Last updated: February 14, 2026