DTC 43

Fig. 045a CODE 43:

Fig. 054b Wiring Diagram Code 43 (ESC):

CODE 43

ELECTRONIC SPARK TIMING (EST)

4.3L "B/G" SERIES

FUEL INJECTION (TBI)

CIRCUIT DESCRIPTION Electronic spark control 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 900 rpm.
Code 43 means the ECM has been low voltage at CKT 485 terminal "B7" for longer than 5 seconds with the engine running or the system has failed a functional check.
This system performs a functional check once per start up to check the ESC system. To perform this test the ECM will advance the spark when coolant is above 95 degrees C and at a high load condition (near wide open throttle). The ECM then checks the signal at "B7" to see if a knock is detected. The functional check is performed once per start up and if knock is detected when coolant is below 95 degrees C (194 degrees F) the test has passed and the functional check will not be run. If the functional check fails the "SERVICE ENGINE SOON" light will stay on until the ignition is turned off or until a knock is detected.

TEST DESCRIPTION These numbers refer to the circled numbers on the diagnostic charts.

1. If the conditions for a Code 43 are present the "Scan" will display "yes". There should not be a knock at idle unless internal engine problems or a system problem exists.
2. This test will determine if the system is functioning at this time. If no knock signal is generated, try tapping on the block near the sensor.
3. Because Code 43 sets when the signal voltage on CKT 485 remains low this test should cause the signal on CKT 485 to go high. The 12 volt signal should be seen by the ECM as "no knock" if the ECM and wiring are good.
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 the 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 to be about 12 volts which would cause the Code 43 functional test to fail.
7. Contacting CKT 496 with a test light to 12 volts should generate a knock signal. This will determine if the ESC module is operating properly.

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 for an open or short to ground.

Also see DIAGNOSIS BY SYMPTOMS.