Purpose.

To provide a method to collect serial data signals indicating wheel sensor acceleration and vehicle speed during exposure to various road surface conditions for developing engine misfire diagnostic algorithm calibrations.

Foreword.

The engine misfire diagnostic detects misfires by monitoring engine speed oscillations. However, the road surface can cause oscillation torque on the drive wheels which also affects the engine speed similar to a true misfire. The misfire algorithm is used to differentiate true misfire conditions from oscillation events caused by road surface. The Electronic Brake Control Module (EBCM) transmits a serial data signal containing wheel sensor acceleration. The Engine Control Module (ECM) receives this wheel sensor acceleration signal and uses this data in the misfire algorithm. The signal data is compared to a threshold point and if it exceeds the threshold, the ECM will turn off the misfire algorithm. The frequency and duration that the misfire algorithm is turned off is monitored by the ECM.

Applicability.

This specification applies to all GM vehicles complying with OBD-II and PPEI 3 and beyond requirements. This specification can be applied for development purposes.

Note: Nothing in the specification supersedes applicable laws and regulations unless specific exemption has been obtained.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.