Powertrain Control Module - PCM

Diagnostic Trouble Code 43:

Knock Sensor Circuit:

CIRCUIT DESCRIPTION
The DTC 43 circuit consists of a knock sensor with one wire that goes directly to the PCM. There are two DTC 43 checks performed by the PCM. One check consists of monitoring the knock signal circuit for a voltage that is more than 4.3 volts and less than 0.64 volt.

DTC 43 WILL SET WHEN
The knock sensor signal is more than 4.5 volts or less than 0.39 volts for more than 16 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate.

DTC 43 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. The first test is to determine if the system is functioning at the present time.

2. Test two determines the state of the 5 volt reference voltage applied to the knock sensor circuit.

DIAGNOSTIC AIDS
The PCM applies 5 volts to knock signal circuit. A 3.9k ohm resistor in the knock sensor reduces the voltage to about 2.5 volts. When knock occurs, the knock sensor produces a small AC voltage that rides on top of the 2.5 volts already applied. An AC voltage monitor in the PCM is able to read this signal as knock and incrementally retard spark.

For further information, refer to Diagnosis By Symptom / Intermittents - Intermittent Malfunctions