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 P0115: Engine Coolant Temperature (ECT) Sensor Circuit
DTC P0120: Throttle Position (TP) Sensor Circuit
DTC P0703: Brake Switch Circuit
DTC P0727: Engine Speed - No Signal
DTC P0826: Up and Down Shift Switch Circuit
DTC P1779: Torque Delivered Signal
DTC P2544: Transmission Torque Request Circuit
DTC P2637: Transmission Torque Delivered Circuit

### Circuit/System Description

The controller area network (CAN) serial data bus is used by the engine control module (ECM) and automatic transmission control module (TCM) to share information. This diagnostic applies to Controller Area Network (CAN) signal failures.

### Conditions for Running the DTC

• | No Lost Communications with the ECM, DTC U0100.

• | The ignition in ON for at least 3 seconds.

• | Not in Emergency Mode.

### Conditions for Setting the DTC

#### DTC P0115

The TCM detects that the engine coolant temperature signal from the ECM is invalid.

#### DTC P0120

The TCM detects that the accelerator position signal from the ECM is invalid.

#### DTC P0703

The TCM detects that the brake pedal signal from the ECM is invalid.

#### DTC P0727

The TCM detects that the engine speed signal from the ECM is invalid.

#### DTC P0826

The TCM detects that the Tap Up/Down mode request or switch status signal from the ECM is invalid.

#### DTC P1779

The TCM detects that the engine air flow torque steady state signal from the ECM is invalid.

#### DTC P2544

The TCM detects that ECM fails to deliver torque control.

#### DTC P2637

The TCM detects that the engine torque signal from the ECM is invalid.

### Action Taken When the DTC Sets

#### DTC P0115

• | DTC P0115 is a Type C DTC.

• | The transmission will default the engine coolant temperature to 80°C (176°F).

#### DTC P0120

• | DTC P0120 is a Type A DTC.

• | The TCM will default Accelerator Position data to 0 percent.

• | The transmission will operate in 5th gear in D or M range, 2nd gear in L range.

#### DTC P0703

• | DTC P0703 is a Type C DTC.

• | The TCM will default the brake pedal signal to off.

#### DTC P0727

• | DTC P0727 is a Type A DTC.

• | The TCM will default engine speed data to 6000 RPM.

• | The TCM will limit engine torque to 270 N·m (199 lb ft).

• | The transmission will operate in 5th gear in D or M range, 2nd gear in L range.

#### DTC P0826

• | DTC P0826 is a Type C DTC.

• | The transmission will disable or inhibit Tap Up/Down mode.

#### DTC P1779

• | DTC P1779 is a Type C DTC.

• | The TCM will default driver requested torque data to 300 N·m (221 lb ft).

#### DTC P2544

• | DTC P2544 is a Type C DTC.

• | The TCM will increase transmission oil pressure to maximum.

• | The TCM will limit the maximum shift speed to 4000 RPM.

#### DTC P2637

• | DTC P2637 is a Type A DTC.

• | The TCM will default engine torque data to 300 N·m (221 lb ft).

• | The TCM will limit engine torque to 270 N·m (199 lb ft).

• | The transmission will operate in 5th gear in D or M range, 2nd gear in L range.

### Conditions for Clearing the DTC

• | DTCs P0120, P0727, and P2637 are Type A DTCs.

• | DTCs P0115, P0703, P0826, P1779, and P2544 are Type C DTCs.

### Reference Information

#### Description and Operation

Electronic Component Description

#### DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

### Circuit/System Verification

1. Start the engine; observe the DTC information with a scan tool. CAN DTCs should not set.
2. Operate the vehicle within the conditions for running the DTC. CAN DTCs should not set.

### Circuit/System Testing

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

⇒ | If no communication with the ECM, refer to Control Module References for further diagnosis.

2. Ignition OFF, disconnect the harness connector of the ECM.
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 ECM.

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 TCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Refer to Control Module References for TCM replacement, setup, and programming.