Code
P1325
FIAT
P — Powertrain
Knock signal circuit fault | Knock sensor signal implausible | Knock measuring circuit fault | Knock control circuit open or short to ground
Views:
UK: 3
EN: 8
RU: 4
AI status
Completed
Completed
100%
Causes
- Faulty knock sensor (open, shorted, or internally failed)
- Damaged, corroded, or disconnected wiring or connector to the knock sensor
- Short to ground or to battery voltage in the sensor circuit
- Poor engine or ECU ground connection
- Oil contamination or mechanical damage to the sensor
- Failed engine control module (rare)
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Reduced engine power or ignition timing retarded (knock control disabled)
- Detonation/pinging under load (if knock control not working properly)
- Poor fuel economy or rough running under load
- Codes may be intermittent and set only under certain loads/temperatures
What to check
- Read and record freeze-frame and related codes with a scan tool
- Check for related codes: crank/cam sensors, grounds, or multiple sensor faults
- Visually inspect knock sensor connector and wiring for damage, corrosion, oil contamination, and proper routing
- Back-probe the sensor connector and measure signal with engine cranking and at idle (use oscilloscope if available)
- Check continuity and resistance of wiring between sensor and ECU connector pins
- Check chassis and engine grounds for integrity
Signal parameters
- Knock sensor generates an AC voltage pulse when engine knock occurs (piezoelectric behavior)
- Typical AC amplitude: small pulses—often ~0.05–1.5 V peak depending on engine/condition (use oscilloscope)
- Characteristic frequency range: several kHz (commonly ~5–15 kHz) for typical knock events
- DC resistance is not reliable on many piezo sensors (may read open or very high); check manufacturer spec if available
- Expected ECU wiring continuity: near 0 ohms between sensor connector and ECU pin for low-voltage reference/ground; signal wire continuity per factory spec
Diagnostic algorithm
- Use a scan tool to read P1325 and any related/secondary codes; note freeze-frame data and conditions when code set.
- Visually inspect sensor, connector, and wiring at sensor and along harness. Repair any obvious damage or corrosion.
- Back-probe sensor connector. With engine cranking or running, check for AC pulses on the signal line using an oscilloscope; verify presence/shape of pulses under load where knock is likely.
- Check continuity between sensor connector and ECU pin; check for shorts to ground or Vb. Repair any open/shorted wiring.
- Verify proper ground(s) for sensor and ECU. Clean/tighten engine and chassis grounds as needed.
- If wiring and grounds are good but signal is absent or implausible, swap in a known-good knock sensor (or temporarily use a replacement) and re-check.
- If a replacement sensor clears the code, reassemble and road test under load to confirm. If fault persists with a known-good sensor, suspect ECU or intermittent wiring; consider ECU bench test or professional diagnosis.
- After repair, clear codes and confirm that P1325 does not return during a full warm-up and load driving cycle.
Likely causes
- Wiring harness damage at sensor or along loom (chafing, pinched, connector corrosion)
- Failed knock sensor (most common)
- Poor ground or connector contact
- Intermittent open/short caused by engine movement or heat exposure
Fault status
Status
Knock sensor signal implausible or knock control circuit open/short detected. ECU may disable knock control/timing advance; check sensor, wiring, and grounds.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email