Attention! Allow the engine to cool completely before removing the oxygen sensor.
The knock sensor responds to an increase in engine vibration, usually caused by detonation of the air/fuel mixture. Based on the information received from the sensor, the system corrects the ignition timing, trying to maintain it at the highest possible level, which guarantees sufficient engine efficiency. The sensor generates an AC signal whose amplitude increases in proportion to the level of vibrations. To compensate for knocking, the ECM/PCM issues a command to shift the ignition timing in the direction of deceleration, if necessary.
Knock sensors are not used on all models, but only on the following:
- a) Civic with D16Y5 engine and CVT;
- b) Civic with D16Y8 engine;
- c) Integra with B18C1 and B18C5 engines.
Examination
1. Disconnect its knock sensor electrical connector and remove the latter from the engine (see accompanying illustration). Reconnect the connector to the sensor. Checking sensors of this type is carried out by registering voltage fluctuations on a voltmeter. Switch the meter to the low AC voltage scale. Connect the negative probe of the meter to the sensor body, the positive probe to the contact terminal. Lightly tap the bottom of the sensor with a hammer to simulate vibration. If the voltmeter does not register voltage fluctuations, the sensor should be replaced.
Note. In principle, this check can be made without removing the sensor from the engine.
Replacement
1. The knock sensor is screwed into the channel of the cooling path of the engine block (see illustration above) and its eversion is associated with certain losses of coolant, which can be avoided by emptying the block in advance (see chapter Current service). Disconnect the electrical connector and remove the sensor from the engine.
2. New sensors are usually shipped with anti-seize coated threads. Screw the replacement sensor into place and tighten it to the required torque. Connect the wiring to the sensor and charge the cooling system (see chapter Current service). Check the engine for signs of coolant leaks.
Note. Overtightening the knock sensor can permanently damage it.