P1618

Steps 1 - 4:

DTC P1618 Serial Peripheral Interface (SPI) PCM Interprocessor Communication Error

Circuit Description
The serial peripheral interface (SPI) communication is used internally by the PCM to send messages between the engine processor and the automatic transmission processor. Included in each message sent between the two-processors is a checksum of the message. Both the engine processor and automatic transmission processor will compare this check sum value with the calculated value. If the checksums don't 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 it's last message was corrupted.

Conditions for Setting the DTC
- Battery voltage is above 9.0 V for 2 seconds.
- The PCM detects an internal program fault (check sum of data communications error).
- Check sum fault present for 3 out 6 seconds.
- No TCM resets for 2 seconds.

Action Taken When the DTC Sets
- The PCM will flash the Check Trans lamp the first time the fault is detected.
- The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.
- The automatic transmission will operate in the safety mode to protect the mechanical parts of the transmission. Shift quality and/or gear changes may not be normal.

Conditions for Clearing the MIL/DTC
- The PCM will turn the Check Trans lamp OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault is no longer present.
- A history DTC P1618 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P1618 can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.