DTC 43

Chart - Code 43 Electronic Spark Control (ESC):

Wiring Diagram for Electronic Spark Control (ESC):

CIRCUIT DESCRIPTION
The knock sensor is used to detect engine detonation and the Electronic Control Module (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, circuit 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 volts DC voltage. The amplitude and signal frequency is dependent upon the knock level.
There are two tests run on this circuit to determine if it is operating correctly. If either of the tests fail, a Code 43 will be set.

A. If circuit 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 a 1/2 second a Code 43 will be stored.

B. This system also performs a functional test to determine if the knock sensor is responding to engine detonation. To perform this test, the ECM will advance the spark under certain load conditions and look for a knock signal response. If knock is detected before conditions are met to run the test, the test is bypassed, but if the test is run and no knock detected the Code 43 will be set.
The test is performed when:
^ The coolant temperature is over 90° C.
^ The Manifold Air Temperature (MAT) is over 0° C.
^ High engine load based on air flow and RPM between 3400 and 4400.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. If the conditions for the "A" test, as described above, are being met the "SCAN" tool will always indicate "yes" when the knock signal position is selected. 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 volt 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 Electronic Spark Control (ESC) portion of the Mem-Cal is faulty.

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

Refer to Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions

If the customer's complaint is the "Service Engine Soon" light comes "ON" when in acceleration, the "B" portion of the code is failing. There is a possibility that the Direct Ignition System (DIS) was in bypass mode when the 43 test was run. An intermittent open in the Electronic Spark Timing (EST) circuit will put the DIS module in bypass which will not allow the spark to be advanced so the 43B test would fail. If ECM also had a 42 stored, then the EST circuit is likely the cause of the Code 43.