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.

The ECM does not detect a valid message from the TCM.

DTC P1601 is a Type B DTC.

DTC P1601 is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Ignition ON, attempt to establish communication with the TCM with a scan tool.

⇒	If no communication with the TCM, refer to for further diagnosis.

2. Ignition OFF, disconnect the harness connector of the TCM.
3. Ignition ON, verify that 1.5-3.4 volts is available between the CAN serial data low and the CAN serial data high circuits.

⇒	If the voltage is not within the specified range, replace the TCM.

4. Ignition OFF, test the CAN communication circuits between the ECM and the TCM for an open, short to ground, or a short to voltage.
5. If the circuits/connections test OK, replace the ECM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine and transmission control module replacement, setup, and programming