Powertrain Controls - ECM/PCM

DTC 43 Knock Sensor Circuit:

Knock Sensor Wiring Diagram:

Circuit Description:

The knock sensor is used to detect engine detonation and the ECM will retard the Ignition Control (IC) based on the signal being received. The circuitry within the knock sensor causes the ECM 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 volts DC voltage. The amplitude and signal frequency is dependent upon the knock level.

If CKT 496 becomes open or shorted to ground, the voltage will either go above 4.6 volts or below 0.89 volt. If either of these conditions are met for about 10 seconds a DTC 43 will be stored.

The test is performed continuously when the following conditions are met.

^ Engine coolant temperature is over 90°C (194°F).
^ IAT temperature is over 0°C (32°F).
^ High engine load based on air flow and RPM between 3400 and 4400.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the conditions for DTC 43, as described above, are being met the scan tool will always indicate "Yes" when the knock signal position is selected. If an audible knock is heard from the engine, repair the internal engine problem, as normally no knock should be detected at idle

2. If tapping on the engine lift hook does not produce a knock signal, try tapping engine closer to sensor

3. The ECM has a 5 volts pull-up resistor which should be present at the knock sensor terminal

Diagnostic Aids:

Check CKT 496 for a potential open or short to ground. - Intermittent Malfunctions

If the customer's complaint is the MIL (Service Engine Soon) comes "ON" when in acceleration. There is a possibility that the electronic ignition system was in bypass mode when the DTC 43 test was run. An intermittent open in the IC circuit will put the ignition control module in bypass which will not allow the spark to be advanced so the DTC 43 test would fail. If the ECM also had a DTC 42 stored, then the IC circuit is likely the cause of the DTC 43.