Code 43, Knock Sensor Circuit: Notes

The knock sensor informs the PCM of engine detonation. The PCM will retard ignition timing based on signals from the knock sensors. Knock sensors produce an AC voltage signal which is proportional to the amount of engine detonation (knock). Internal sensor circuitry causes the 5-volt DC reference signal sent by the PCM to be pulled low to about 1.5 volts. Any AC voltage produced by the sensors will travel to the PCM on this same reference line. Code 43 will set if: one sensor circuit becomes open, resulting in a 2.2 to 4.1-volt reference being monitored by the PCM, both sensor circuits become open, resulting in a reference voltage greater than 4.1 volts being seen by the PCM, or one or both circuits become grounded, resulting in a low (less than .78 volt) reference voltage being seen by PCM.

If an audible knock is heard from the engine, repair the internal engine problem, as normally no knock should be detected at idle. The PCM supplies 5 volts on the knock sensor circuit which should be present at the knock sensor terminals when the sensors are disconnected.

If knock sensor circuit is shorted to voltage, Code 43 will set. With both sensors and PCM disconnected, no voltage should be present. An improperly installed sensor can prevent the knock sensor from grounding to the block.