Circuit Description

The serial peripheral interface (SPI) communication is used internally by the engine control module (ECM) to send messages between the engine processor and the message sent between the 2 processors is a checksum of the message. Both the engine processor automatic transaxle processor will compare this checksum value with the calculated checksum. If the checksums do not match, the processor will review the new data as being corrupted and ignore the value. The processor then uses the previous message. The receiving processor will then send a message to the sending processor informing it that its last message was corrupted.

The ECM monitors periodic transmission control module (TCM) status messages and if the message is not received, the fail counter is incremented and the diagnostic trouble code (DTC) will be stored.