Circuit Description
The serial peripheral interface (SPI) communication is used internally by the engine control module (ECM) to send a message between the engine processor and the automatic transaxle processor. Included in each 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 calculated checksum. If the checksum do not match, the processor will review the new data as being corrupted and ignore the value. The processors 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.
The ECM monitors periodic transmission control module (TCM) status messages and if a message is not received, a fail counter increments and a DTC will be stored.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1601 Lost Communication with TCM
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The ignition voltage is more than 11 volts. |
| • | The engine is running more than 2 seconds. |
| • | No output controls are active. |
Conditions for Setting the DTC
The ECM does not detect a valid message from the TCM.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |
2 |
Is the repair complete? | Go to Step 3 | -- |
3 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 4 |
4 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK |
