Knock sensor

The purpose of this test is to evaluate the correct operation of an engine piezoelectric knock sensor when subjected to a simulated engine knock.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Connect PicoScope to the Knock Sensor.
     
  2. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
     
  3. Select GO or press the space bar to see live data.
     
  4. Simulate an engine knock by tapping lightly on the engine block with a metallic object and observe your screen.
     

Example waveform

Waveform notes

This known good waveform has the following characteristics:

An initial spike as the engine block is tapped, followed by reduced oscillations as the ringing and output from the piezo crystal dissipates.

Waveform Library

Go to the drop down menu bar at the lower left corner of the Waveform Library window and select, Knock sensor.

Further guidance

A motor vehicle petrol engine is expected to produce a good power output with minimal fuel consumption and exhaust emissions.  It is therefore important that the mapping of the ignition advance curve is as near to detonation, Knocking/pinking as possible. The optimal point at which the spark plug ignites the air/fuel mixture is just before detonation occurs. It is inevitable that at certain times and under certain conditions detonation will occur. The frequency of the vibration caused by this is about 15 kHz.

Detonation is damaging to the engine and if unchecked it will cause hot spots within the combustion chamber which will lead to component failure.

To avoid such situations a knock sensor is fitted to some management systems. The sensor is small piezoelectric device that when connected to the ECM, or internal detonation control processor, can identify the 15 kHz signal and retard the ignition timing.

The ECM control circuit continues to monitor the frequency delivered by the sensor on subsequent engine rotations and gradually releases the timing retardation until the ignition timing is back at its original mapped setting.

An engine running on a retarded ignition setting will have a noticeable lack of power and over an extended period of time may also cause overheating in the exhaust system.

It is also a possibility that mechanical faults will produce vibrations that can be interpreted by the ECM as detonation.

Detonation occurs if any of the following are present.

  • Very high combustion temperatures.
  • Over-advanced ignition timing.
  • Lean air/fuel ratio causing high temperature.
  • Carbon deposits pre-igniting the air/fuel mixture.

Diagnostic trouble codes

Selection of Diagnostic Trouble Codes (DTCs):

P0324 - Knock Sensor (KS) Module Performance

P0325 - PCM Knock Sensor Circuit

P0326 - Knock Sensor Circuit Excessive Spark Retard

P0327 - Knock Sensor Circuit Low Voltage

P0328 - Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)

P0329 - Knock Sensor 1 Circuit Intermittent (Bank 1 or Single Sensor)

P0330 - Knock Sensor (KS) Circuit Bank 2

P0331 - Knock Sensor 2 Circuit Range/Performance (Bank 2)

P0332 - Knock Sensor 2 Circuit Low Input (Bank 2)

P0333 - Knock Sensor 2 Circuit High Input (Bank 2)

P0334 - Knock Sensor 2 Circuit Intermittent (Bank 2)

P1602 - Knock Sensor (KS) Module Performance

GT021-5

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • Large Dolphin/Gator Clips

    £10.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £47.00

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Guided test: Knock sensor