Circuit Description

Electronic spark control is accomplished with the ESC module. The module sends a voltage signal to the ECM. As knock sensor detects engine knock, voltage from ESC module to ECM drops. This signals ECM to retard timing. ECM will retard timing when knock is detected, and RPM is above about 900 RPM.

Code 43 means the ECM has seen low voltage at circuit No. 485 (terminal "B7") for more than 5 seconds with engine running, or system has failed functional check.

This system performs a functional check once per start-up to check ESC system. To perform this test, ECM will advance spark when coolant temperature is above 203°F (95°C), and a high load condition is present (near wide open throttle). The ECM then checks signal at terminal "B7" to determine if knock is detected. If knock is detected when coolant temperature is below 203°F (95°C), the test has passed and the functional check will not be run. If the functional check fails, the "SERVICE ENGINE NOW" light will remain on until ignition is turned off, or until a knock signal is detected.