Knock sensor, is a device using piezoelectric effect, it’s also known as KNK. This knock sensor will always make sure your vehicle run close to that detonation point, and to ensure to deliver fuel efficiency and power. When engine detonation occurs, vibration of the cylinder blocks causes the sensor to generate a voltage signal. Normally 1 sensor for 4 cylinder engine and 2 sensor for 6 and 8 cylinder engine. Obviously knock sensor are critical for turbo and supercharged cars.

There are two types of knock sensors used on Toyota engines.

i) The mass type sensor, which produces a voltage output over a wide input frequency range (vibration frequency is about 7KHz). The ECU uses a filter circuit to identify between background noise and actual engine knock.

ii) The resonance sensor, is tuned into a very narrow frequency band and only produces a certain signal voltage when exposed to vibration in the range of 7KHz. The ECU requires less complicated filter curcuit with this type of sensor.

ECU Detonation Control

Below is how Knock sensor works with ECU…

when there’s a detonation taking place, it retards ignition timing until the knocking stop. The the timing advanced back to normal or calculated value. Due to this ignition system will operates at maximum performance. If the ECU noted that the knock retard is not workingm it will enter a fail-safe mode and fix the retard angle to prevent engine damage.

Here’s the location of the knock sensor on 4AGE 20V, just below the Intake manifold.
Purge Valve (top) and Knock sensor (below)

It should look something like this…

Symptoms

Drivability problems including a lack of power and perhaps some hesitation also increase of fuel consumption. There may also be other symptoms.

Causes

i) The knock sensor is faulty and need to be replaced
ii) There is a wiring shoft/failure in the knock sensor circuit. Check properly because sometimes after change the knock sensor problem or error code still shows…
iii) Also check for special ground shield that cover the signal wire running from the sensor to the sensor. The shield sourrounds the signal wire is connected to ground so if any electrical interference is taken to ground.

sometimes the engine light won’t come out, therefore no error code were found, but some say that they just replace the knock sensor thier car feel like new, in other hand they replace the knock sensor there’s not much different, later they found out that the wiring was faulty…so becarefull…

How to test a knock sensor.

i) By removing the knock sensor, check if there is no continuity between the terminal and body (based on 4A-GE repair manual, page F1-67)
ii) checking the diagnosis code


# 52 #1 Knock sensor 
  • no KNK1 signal to ECU
  • knock sensor (looseness)
  • malfunctioning knk sensor
# 53 #2 Knock sensor
  • no KNK2 signal to ECU
  • same as above

source : Club4AG

iii) used the OBDII Scan tool
iv) tapping tools or hammer on the block near the sensor (don’t hit the sensor !!!) and watch the timingchange using the timing gun or scan tool while idling, if the timing fails to retard, the sensor may be faulty, replace it. See the picture below.

Sometimes a knock sensor will react to sounds other than those produced by detonation. A noisy mechanical fuel pump, a bad water pump or alternator bearing, or a loose rod bearing can all produce vibrations that can trick a knock sensor into retarding timing.