Circuit Description

The PCM contains integrated Knock Sensor (KS) diagnostic circuitry. An input signal from KS is used to detect engine detonation, allowing PCM to retard Ignition Control (IC) spark timing based on amplitude and frequency of KS signal being received. The KS produces an AC signal under all engine operating conditions. During engine operation, PCM calculates average voltage of KS signal. If the knock sensor system is operating normally, PCM will see KS signal voltage vary at greater or less than the calculated voltage average. If PCM detects KS input signal equals to the KS average voltage for longer than 95 percent of calibrated time, DTC will set. Conditions for setting DTC:

• No CMP, CKP, ECT or VSS sensor DTCs set.
• ECT greater than 167°F (75°C).
• TP angle greater than 15 percent.
• Engine running for longer than 30 seconds.
• Engine load greater than 45 percent.
• Engine speed is 1000-5000 RPM.
• Maximum spark retard is less than 15 percent.
• System voltage greater than 9 volts.
• PCM detects a KS signal voltage within the calculated average voltage range for at least 10 seconds.