Code
P1303
DS
P — Powertrain
Knock adjustment malfunction
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UK: 0
EN: 3
RU: 1
AI status
Completed
Completed
100%
Causes
- Faulty knock sensor (electromechanical failure or internal short)
- Open, shorted or corroded knock sensor wiring or connector
- Poor ground or power supply to engine control module (ECM)
- Faulty or intermittent ECM/PCM
- Excessive engine mechanical noise (detonation from carbon, low octane fuel, lean condition)
- Ignition system faults causing false knock signals (bad coils, plugs, timing incorrect)
Symptoms
- MIL (Check Engine Light) illuminated
- Reduced engine performance or limp/limited power mode
- Retarded ignition timing or reduced ignition advance
- Poor fuel economy
- Intermittent or persistent knocking/pinging noise from engine
- Possible rough running or misfire-like behavior under load
What to check
- Read freeze-frame and stored data with a capable scan tool; note engine load, rpm, coolant temp, and any related codes
- Inspect knock sensor connector and wiring for corrosion, damage, chafing or pinched wires
- Check ECM and engine grounds and power supply voltages
- Monitor live data for knock count, knock sensor voltage or frequency, ignition timing advance/retard and fuel trims
- Perform a visual engine inspection for carbon deposits, vacuum leaks, damaged ignition components or fuel issues
- Check for related codes (ignition, fuel trim, cam/crank sensors) that could explain knock readings
Signal parameters
- Knock sensor raw voltage or mV level (AC/PK-PK depending on sensor type)
- Knock event count / knock amplitude
- ECM command for timing advance/retard (ignition timing adjustments)
- Engine speed (RPM) and load (MAP/MAF) at time of events
- Fuel trim and ignition timing values correlated with knock events
- Sensor impedance/resistance if applicable (ohms)
Diagnostic algorithm
- Retrieve all DTCs and freeze-frame data. Note conditions when P1303 set (rpm, load, temp). Clear codes and road test to reproduce.
- Visually inspect the knock sensor, its mounting, connector and wiring harness for damage, heat exposure or oil contamination. Repair as needed.
- Check sensor wiring continuity and insulation to ECM pins with meter (backprobe). Look for shorts to ground or power and intermittent opens while flexing harness.
- Verify engine ground points and ECM supply voltages. Clean and secure grounds; retest.
- Use a scan tool or oscilloscope to monitor knock sensor signal while engine is at operating temperature under load. Look for expected waveform, amplitude and knock counts. Compare to known-good values if available.
- If signal is absent, out of range, or noisy, disconnect sensor and measure its resistance per manufacturer spec. Replace sensor if out of spec or fails oscilloscope test.
- If sensor and wiring check OK, inspect ignition system (spark plugs, coils, timing) and fuel system (injectors, trims, fuel pressure) to eliminate conditions causing real knock.
- Consider ECM software update or reflash if bulletins exist for knock control faults. If ECM suspects faulty internal processing and other components verified good, evaluate ECM replacement.
- After repairs, clear codes and perform targeted road test under the same conditions. Verify no P1303 returns and that timing/knock counts behave normally.
Likely causes
- Faulty or contaminated knock sensor
- Damaged sensor wiring or poor connector connection
- ECM misinterpreting signal due to grounding or supply issue
- Engine mechanical detonation (carbon build-up or incorrect fueling/ignition)
Fault status
Status
Malfunction stored: ECM detected abnormal knock control behavior and inability to perform knock-based ignition adjustments. MIL illuminated and freeze-frame data logged.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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