Code 43: Electronic Spark Control: Notes

Electronic Spark Control (ESC) is accomplished using a knock sensor and a control module which sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, signaling the ECM to retard timing. The ECM will retard the timing when knock is detected and engine speed is greater than 900 RPM.

Code 43 means the ECM has seen low voltage on circuit No. 485 (terminal "B7") for longer than 5 seconds with the engine running, or the system has failed the 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 temperature is greater than 194°F (95°C) and a high load condition exists (near WOT). If knock occurs, the functional test has passed. If the ECM detected knock before coolant temperature reached 194°F (95°C), the system is operating properly and the functional check will not be run. If the functional check fails, the "SERVICE ENGINE SOON" light will remain on until ignition is turned off, or until a knock signal is detected.

1. If the conditions for a Code 43 exist, the "Scan" tester 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 properly 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 closer to the area of the sensor.
3. Because Code 43 sets when the signal voltage on circuit No. 485 remains low, this test should cause the signal on circuit No. 485 to go high. The 12-volt signal should be seen by the ECM as "no knock" if the ECM and wiring are okay.
4. This test will determine if the knock signal is being detected on circuit No. 496, or if the ESC module is at fault.
5. If circuit No. 496 is routed to close to secondary ignition wires, the ESC module may see the induced interference as a knock signal.
6. This checks the ground circuit to the module. An open ground will cause the voltage on circuit No. 485 to be about 12 volts, which would cause the Code 43 functional tests to fail.
7. Touching circuit No. 496 with a test light to 12 volts should generate a knock signal. This will determine if the ESC module is operating correctly.