Without 4L80E Automatic Transmission

Electronic Spark Control Circuit Code 43:

Electronic Spark Control Circuit:

Circuit Description:
Electronic Spark Control (ESC) is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the ECM to retard timing. The ECM will retard the timing when knock is detected and rpm is above about 900 rpm.

Code 43 means the ECM has seen low voltage at CKT 485/457 terminal "B7" for longer than 5 seconds with the engine running or the system has failed the functional check.

The ECM continually monitors voltage on CKT 485/457 terminal "B7" if a knock signal (low voltage) is detected but for less than 5 seconds the ESC system is considered operational and Code 43 will not set. If, however, low voltage is detected for more than 5 seconds or signal voltage remains high, a functional check will be performed. To perform this, the ECM will advance the spark timing when coolant temperature is above 95°C and the engine is under heavy load (near WOT). The ECM then checks the signal voltage at "B7" to see if a knock is detected. If no knock is detected "Service Engine Soon" light will remain "ON" until the ignition is turned "OFF" or until a knock signal is detected. The functional check will only be performed once per start up.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

1. If the conditions for a Code 43 are present, the Tech 1 "Scan" tool will always display "YES." There should not be a knock at idle unless an internal engine problem, or a system problem exists.

2. This test will determine if the system is functioning at this time. Usually a knock signal can be generated by tapping on the right exhaust " manifold. If no knock signal is generated, try tapping on block close to the area of the sensor.

3. Because Code 43 sets when the signal voltage on CKT 485/457 remains low, this test should cause the signal on CKT 485/457 to go high. The 12 volts signal should be seen by the ECM as "no knock" if the ECM and wiring are OK.

4. This test will determine if the knock signal is being detected on CKT 496 or if the ESC module is at fault.

5. If CKT 496 is routed to close to secondary ignition wires, the ESC module may see the interference as a knock signal.

6. This checks the ground circuit to the module. An open ground will cause the voltage on CKT 485/457 to be about 12 volts which would cause the Code 43 functional test to fail.

7. Connecting CKT 496 with a test light to 12 volts should generate a knock signal. This will determine if the ESC module is operating correctly.


Diagnostic Aids:
Code 43 can be caused by a faulty connection at the knock sensor at the ESC module or at the ECM. Also check CKT 485/457 for possible open or short to ground.

- Intermittent Malfunctions