P2355 – Cylinder 4 Knock Sensor Circuit

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit | Location: Cylinder 4

Definition source: SAE J2012/J2012DA (industry standard)

DTC Structure (SAE J2012)

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

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.

P2355 indicates the powertrain control module has detected an electrical fault in the cylinder 4 knock sensor circuit. This code is about the circuit and signal path (sensor, wiring, connectors, and module interfaces), not a guaranteed mechanical knock condition by itself. The exact detection logic, enabling conditions, and what the module considers “faulted” can vary by vehicle, engine configuration, and calibration. Always confirm component locations, connector pinouts, and test specifications using the correct service information before testing or replacing parts.

What Does P2355 Mean?

P2355 means the control module has identified a problem in the Cylinder 4 Knock Sensor Circuit. Under SAE J2012 DTC structure, this entry is used when the module’s monitoring for the cylinder 4 knock sensor input circuit indicates an electrical/circuit-related issue, such as a loss of signal integrity or an implausible circuit condition caused by wiring, connectors, the sensor, or the module’s input circuitry. Because designs vary by vehicle, “cylinder 4 knock sensor” may refer to a dedicated sensor, a bank-mounted sensor mapped to cylinder 4, or an input channel associated with cylinder 4 knock processing in the control strategy.

Quick Reference

• System: Powertrain
• Official meaning: Cylinder 4 Knock Sensor Circuit
• Standard: ISO/SAE Controlled
• Fault type: Circuit
• Severity: MIL may illuminate; the module may reduce spark advance or alter knock control strategy, which can affect performance and fuel economy.

Symptoms

• MIL/Check engine light: Lamp illuminated with P2355 stored as current or pending.
• Reduced performance: Noticeable loss of power if the module applies a conservative ignition strategy.
• Poor fuel economy: Increased consumption due to less optimal timing control.
• Roughness under load: Hesitation or uneven acceleration during moderate to heavy throttle.
• Limited acceleration: Slower response to throttle inputs, especially during climbs or passing.
• Additional DTCs: Related knock sensor or circuit codes may accompany P2355 depending on the system design.

Common Causes

• Connector issues: Loose, corroded, oil-contaminated, or water-intruded knock sensor connector affecting the cylinder 4 knock sensor circuit.
• Harness damage: Chafed, pinched, melted, or rubbed-through wiring in the knock sensor circuit, especially near engine hot spots or sharp brackets.
• Open circuit: Broken conductor inside the insulation, poor crimp, or partially backed-out terminal creating an intermittent or permanent open in the circuit.
• Short to ground: Insulation damage causing the signal/reference to contact ground, pulling the circuit low or distorting the signal.
• Short to power: Harness contact with a powered feed or reference circuit causing an abnormal signal level on the knock sensor circuit.
• High resistance: Terminal fretting, poor pin fit, or corrosion increasing resistance and weakening or corrupting the knock sensor signal path.
• Sensor fault: Internal knock sensor failure (or incorrect sensor type installed) causing an invalid or missing response on the cylinder 4 circuit.
• ECM/PCM input issue: Rare fault in the control module’s knock sensor input circuitry or internal processing for that channel.

Diagnosis Steps

Tools typically needed include a scan tool with live data and freeze-frame access, a digital multimeter, and vehicle-specific wiring diagrams/service information. Back-probing tools, terminal inspection picks, and a suitable load/light or resistor substitute (as allowed by service info) can help validate circuit integrity. If available, use a lab scope for signal visualization, but confirm test methods and connector pinouts in service information because designs vary by vehicle.

1. Confirm the DTC and context: Scan all modules for codes, record P2355 along with any related knock sensor, misfire, or power supply/ground DTCs, and save freeze-frame data to understand the operating conditions when the fault set.
2. Check for obvious mechanical contributors (without assuming): Verify the engine is not exhibiting severe noise, loose components, or missing fasteners that could influence knock sensing. If abnormal noises exist, address them as a separate concern while continuing circuit checks.
3. Review service info for cylinder mapping: Confirm which knock sensor or circuit is designated for “Cylinder 4” on that platform (some engines use multiple sensors and different channel naming). Use the correct connector views, pin numbers, and test procedure.
4. Visual inspection of the circuit: With ignition off, inspect the knock sensor connector(s) and harness routing for rubbing, heat damage, oil saturation, corrosion, or evidence of prior repairs. Pay close attention to areas where the harness bends or is clipped to the engine.
5. Connector and terminal check: Disconnect the sensor connector and inspect terminals for spread pins, poor tension, pushed-back terminals, or fretting. Reseat connectors fully and ensure any secondary locks are engaged. If corrosion is present, follow approved terminal cleaning/repair practices.
6. Wiggle test with live data logging: Reconnect components, run the engine if allowed by service info, and monitor knock sensor-related live data or counters while gently manipulating the harness and connector. Log data so you can correlate signal changes with harness movement; do not pull on wires at the connector.
7. Power/ground and reference integrity checks: Using the wiring diagram, verify any required power supply, sensor reference, and ground paths that support the cylinder 4 knock sensor circuit. Perform voltage-drop testing across grounds and feeds under the same conditions the circuit operates (consult service info for the correct way to load the circuit).
8. Circuit continuity and short checks: With the circuit safely powered down as required, measure continuity end-to-end between the sensor connector and the control module connector for the relevant signal/return circuits. Then check for shorts to ground and shorts to power on each circuit leg. Compare results to service information specifications; do not rely on generic thresholds.
9. Signal evaluation (if supported): If a lab scope is available and service info permits, observe the knock sensor signal while the engine runs and during controlled test conditions. Look for a dead channel, excessive noise, or a signal that collapses when harnesses are moved, indicating wiring/terminal faults.
10. Component substitution only after circuit checks: If wiring, terminals, and supporting feeds/grounds test good, follow service information to test the sensor itself and replace it only if it fails. If the sensor is known-good and the fault persists, follow OEM pinpoint tests for the ECM/PCM input channel before considering module replacement.

Professional tip: When P2355 is circuit-related, intermittent terminal contact is common. If the code sets sporadically, prioritize a thorough terminal tension check and a harness wiggle test while logging live data; a brief signal dropout often won’t show in a quick glance at the scan tool, but it will appear in a recorded log and helps pinpoint the exact harness segment or connector that’s failing.

Possible Fixes

• Repair wiring damage: Restore any chafed, pinched, melted, or broken wiring in the Cylinder 4 knock sensor circuit using proper splices, sealing, and routing to prevent repeat faults.
• Clean and secure connectors: Clean corrosion/contamination, correct bent or backed-out terminals, improve terminal tension (poor pin fit), and ensure connectors are fully seated and locked.
• Address power/ground issues: Repair opens/high resistance in shared sensor grounds, shields, or reference feeds (varies by vehicle), including loose ground points or damaged ground splices that affect the circuit.
• Replace the knock sensor (if proven faulty): Replace only after circuit integrity checks confirm the sensor is the source of the abnormal circuit behavior.
• Repair shielding/interference problems: Restore damaged shielding or reroute wiring away from high-current components if testing indicates induced electrical noise is corrupting the knock sensor circuit signal (implementation varies by vehicle).
• ECM/PCM connector service: Inspect, clean, and repair module-side terminals for fretting, corrosion, water intrusion, or pin fit issues affecting the knock sensor circuit.
• ECM/PCM replacement or reprogramming (last resort): Consider only after all circuit tests pass and service information supports a module fault or calibration update for this DTC.

Can I Still Drive With P2355?

You can often drive short distances with P2355, but it’s best to treat it as a powertrain electrical fault that can affect ignition timing strategy and drivability depending on how the vehicle uses the Cylinder 4 knock sensor input (varies by vehicle). If the engine runs rough, has reduced power, stalls, or the vehicle enters a protective mode, avoid driving and diagnose promptly. Also do not continue driving if any safety-related warnings appear or if the vehicle exhibits unpredictable acceleration response; arrange inspection and repair instead.

What Happens If You Ignore P2355?

Ignoring P2355 can lead to recurring warning lights, reduced performance, poor fuel economy, and drivability complaints if the control module substitutes a default strategy due to an unreliable Cylinder 4 knock sensor circuit signal. Over time, an unresolved circuit problem may worsen (intermittent becomes constant) as wiring or terminal damage progresses. It can also complicate diagnosis of other issues because a faulty circuit can cause misleading data and additional fault codes, increasing repair time and the chance of unnecessary parts replacement.

Last updated: February 14, 2026