Code 41 - OPTI-Spark Ignition System (Open Or Shorted Est): Notes

Ignition system provides 2 timing inputs to ECM, high resolution (360 pulses per camshaft revolution) and low resolution (8 pulses per camshaft revolution). ECM uses these 2 inputs to determine individual spark timing for each cylinder. Once ECM calculates ignition timing, timing signal will be sent to ignition coil driver on EST circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. EST signal voltage ranges from about .5 volt to 4.5 volts. If a Code 41 is set, ECM will disable fuel injectors to prevent flooding of engine.

1. Code 41 will set if EST circuit voltage exceeds 4.6 volts and engine speed is less than 1500 RPM.
2. Without engine running or cranking, voltage would not be present on EST line.
3. This step determines if EST signal from ECM is available at ignition coil driver. EST circuit voltage should be between about .5 volt and 4.5 volts.
4. Remaining steps ensure coil driver circuitry is okay.
5. If all wiring and connections are okay, check ignition coil and ignition coil voltage supply.