DTC 43

Electronic Spark Control (ESC - Knock Sensor) Circuit Diagram:

CIRCUIT DESCRIPTION
The knock sensor is used to detect engine detonation and the PCM will retard the electronic spark timing based on the signal being received, The circuitry within the knock sensor causes the PCM's supplied 5 volt signal 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 frequency are dependent upon the intensity of the knock.

The Mem-Cal used with this vehicle contains the functions which were part of the remotely mounted ESC modules used on other GM vehicles. The ESC portion of the Mem-Cal then sends a signal to other parts of the PCM which adjusts the spark timing to reduce detonation.

If the voltage in the signal line from the knock sensor (circuit 946) goes above 4.8 volts (open circuit) or below 0.64 volt (circuit shorted to ground), for more than 10 seconds, then Code 43 will set. The PCM monitors voltage in the ESC circuit when the engine is at normal operating temperature, IAT sensor indicates air temperature over 0°C (32°F), engine is under load, and engine speed is between 3400 and 4400 rpm.

TEST DESCRIPTION

Code 43 Diagnostic Chart:

Numbers below refer to circled numbers on diagnostic chart.
1. If the conditions for a Code 43 as described above are present, the "SCAN" tool will always indicate "YES" when the knock signal position is selected. If an audible knock is heard from the engine, there is an internal mechanical problem in the engine (there should be no knocking with the engine idling. Detonation or "PING" only occurs when an engine is under some load.)
2. If tapping on the engine hook does not produce a knock signal, try tapping on the engine block near the sensor.

DIAGNOSTIC AIDS
^ Check circuit 496 for open or short to ground.
^ Also check for improper installation of MEM-CAL.
^ If the customers complaint is the "SES" light comes "ON" during acceleration, the B portion of the code is failing. It's possible that the system was in bypass mode while testing for the Code 43. An intermittent open in the EST circuit will put the DIS module in bypass mode, which will not allow the spark to be advanced, causing the 43B test failure. If a Coe 42 is also stored, the EST circuit is likely the cause of Code 43 also.