Powertrain Controls - ECM/PCM

CIRCUIT DESCRIPTION
The knock sensor is used to detect engine detonation and the ECM will retard the electronic spark timing 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 A/C 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 3.5 volts or below 1.5 volts. If either of these conditions are met for about 5 seconds, a Code 43 will be stored.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Code 43 will set when:
^ Coolant temperature is over 90°C.
^ MAT temperature is over 0°C.
^ High engine load based on MAP and rpm.
^ Voltage on CKT 496 goes above 3.5 volts or below 1.5 volts.
^ All conditions present for 5 seconds 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 before proceeding.
3. The ECM has a 5 volts pull-up resistor, which should be present at the knock sensor terminal.
4. This test determines if the knock sensor is faulty or if the ESC portion of the Mem-Cal is faulty.

DIAGNOSTIC AIDS
Check CKT 496 for a potential open or short to ground. Also check for proper installation of Mem-Cal.

Refer to "Intermittents" in Symptoms. - Intermittent Malfunctions