Powertrain Controls - ECM/PCM

DTC 43 Chart:

Knock Sensor Circuit:

Circuit Description:
The Knock Sensor (KS) is used to detect engine detonation. The PCM receives the knock sensor signal and will retard Ignition Control (IC) timing until knock is not detected.

The circuitry within the KS will drop approximately half of the 5 volts applied to the sensor on CKT 496. When engine detonation occurs, the sensor produces an A/C signal which rides on the 2.5 volt DC signal. The voltage amplitude and frequency is dependent upon the knock level emitted from the engine combustion process.

DTC 43 Will Set When:
The PCM detects above 4-6 volts or below .89 volt for 10 seconds, 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. This test will be performed continuously when all these conditions are met.

Action Taken (PCM will default to):
The MIL will become illuminated. Knock retard will be fixed at 15° of timing retard.

DTC 43 Will Clear When:
A current DTC 43 will clear when the PCM senses the signal voltage level between 0.89 and 4.6 volts. A history DTC 43 will clear after 50 consecutive ignition key cycles without a current DTC being stored.

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 Tech 1 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. The PCM applies a 5 volt signal to the sensor on CKT 496.

Diagnostic Aids:
Check CKT 496 for a potential open or short to ground.

Refer to "Intermittents" in "Diagnosis By Symptom." - 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 PCM also had a DTC 42 stored, then the IC circuit is likely the cause of the DTC 43.