For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P1601: Lost Communication with TCM

### Circuit/System 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.

### Conditions for Running the DTC

• | The ignition is ON.

• | The engine is running greater than 2 seconds.

• | The ignition 1 voltage is greater than 11 volts.

• | 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

DTC P1601 is a Type B DTC.

### Conditions for Clearing the DTC

DTC P1601 is a Type B DTC.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

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 at the TCM.
3. Ignition ON, test for 1.5-3.4 volts between the CAN serial data low terminal A7 and the CAN serial data high circuit terminal A17.

⇒ | If 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 test normal, test or replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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