Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / P1386 — Knock sensing test pulse

P1386 — Knock sensing test pulse

Detailed page for trouble code P1386.

34,510codes
59brands
11,925generic
22,585specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

P1386

PORSCHE P — Powertrain

Knock sensing test pulse

Brand: PORSCHE
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty knock sensor (piezo element degraded or cracked)
  • Open, shorted or high-resistance wiring in the knock sensor circuit
  • Corroded, loose or contaminated sensor connector or pins
  • Poor engine/ECU ground or power supply issue
  • Intermittent connection or chafed harness (intermittent shorts during vibration)
  • ECU internal fault or failed test-pulse driver

Symptoms

  • Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
  • Possible ignition timing knock retard — reduced performance or hesitation
  • Intermittent misfires or rough idle under some conditions
  • Diagnostic trouble code stored; may trigger limp or reduced performance modes on some models
  • Noise from engine area if sensor mounting loose

What to check

  • Read freeze frame and live data; note conditions when code set (RPM, load, temperature)
  • Visual inspection of knock sensor(s), mounting, and connector for damage, corrosion, or oil contamination
  • Wiggle-test wiring while monitoring for intermittent changes in live data or reported faults
  • Back-probe sensor connector and measure signal response with an oscilloscope while cranking/running
  • Check continuity and resistance between sensor and ECU pins; inspect for shorts to ground or battery voltage
  • Verify engine and ECU grounds are secure and corrosion-free

Signal parameters

  • Sensor type: piezoelectric knock sensor (produces AC voltage in response to vibration)
  • Typical sensor output: AC millivolt-level signal (tens to a few hundred mV) when knock occurs — model-specific
  • ECU test pulse: short diagnostic pulse injected by ECU on the knock circuit; expected to produce a defined response measured by the ECU
  • Expected behaviour: sensor circuit should return to idle voltage and exhibit no open/short when test pulse applied — refer to Porsche service manual for exact pulse width and thresholds
  • Use an oscilloscope to confirm presence of test pulse at the ECU pin and a valid AC response from the sensor while cranking/running

Diagnostic algorithm

  1. Retrieve full DTC list and freeze-frame data; note operating conditions when P1386 set.
  2. Clear codes and attempt to reproduce; if code returns, proceed with inspection.
  3. Perform visual inspection of the knock sensor(s), mounting point and connectors. Repair any obvious damage, corrosion or loose mounting.
  4. Verify engine and ECU ground points are clean and secure.
  5. Backprobe the knock sensor connector. With key on/engine off, check for unexpected voltages (no constant supply voltage should be present on a passive piezo sensor circuit unless manufacturer specifies).
  6. Start engine and monitor knock sensor waveform with an oscilloscope. Look for AC activity and the ECU test pulse; compare to known-good waveform or Porsche specs.
  7. Check continuity and resistance of the sensor wiring to the ECU; isolate and repair any open circuits or shorts to ground/battery.
  8. If wiring and grounds are good but no valid sensor response, swap or bench-test the knock sensor (if a known-good sensor is available) and re-test.
  9. Inspect for engine mechanical noise sources or loose mountings that could alter sensor readings.
  10. If sensor and wiring check OK and test pulse not present or ECU response abnormal, check for ECU software updates or consider ECU diagnostic/repair as a last resort.
  11. After repair, clear codes and road-test under conditions that originally set the code to confirm the fault is resolved.

Likely causes

  • Damaged or contaminated sensor connector
  • Broken or shorted harness between sensor and ECU
  • Failed knock sensor element
  • Poor ground at engine or ECU

Fault status

⚠️ Status
ECU detected an abnormal or missing response to its knock-sensing test pulse on the knock sensor circuit. Indicates possible sensor, wiring/connector, ground or ECU/test-circuit fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 3.0 hours (varies by model and access to sensor/wiring)

Similar codes

P0325 P0327 P0328 P0330 P0335
136

Browse 136 PORSCHE manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

PORSCHE

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .