System Operation

Electronic Spark Control (ESC) circuitry of the ECM retards ignition timing in response to engine detonation. A detonation sensor detects engine knock. The ECM uses detonation sensor inputs to retard ignition timing. A 5-volt reference signal is sent from the ECM to the detonation sensor. ECM internal circuitry reduces the 5-volt signal to 2.5 volts. If engine knock is detected, detonation sensor sends an AC voltage back to the ECM. Amplitude and frequency of AC signal depends on amount of engine knock present. ECM senses AC voltage and retard ignition timing.

A code 43 will be set if the ECM senses a detonation sensor voltage signal above 3.5 volts (shorted to ground), or below 1.5 volts (open circuit), for about .6 seconds. A code 43 can also be set if the detonation sensor produces an AC signal longer than 3.7 seconds during a 3.9 second period.