P1618

P1618 PCM/ECM Internal SPI Communication

Circuit Description
The Serial Peripheral Interface (SPI) communication is used internally by the powertrain control module (PCM)/engine control module (ECM) to send messages between the engine processor and the automatic trans axle processor. Included in each message sent between the two processors is a checksum of the message. Both the engine processor and the automatic transaxle will compare this checksum value with the calculated value. If the checksums do not match, the processor will view the new data as being corrupted and ignore the values. The processor will then use the previous message. The receiving processor will then send a message to the sending processor informing it that its last message was corrupted.

Conditions for Setting the DTC
- Battery voltage is greater than 9 volts for more than 2 seconds.
- Ignition ON.
- No PCM/ECM resets for more than 2 seconds.

Action Taken When the DTCs Sets
- The PCM/ECM will illuminate the Malfunction Indicator Lamp (MIL) the first time the fault is detected.
- The PCM/ECM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The PCM/ECM will turn the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault is no longer present.
- A history DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC can be cleared by using the scan tool.