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 P0826: Up and Down Shift Switch Circuit
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 engine run time is greater than 5 seconds.

• | No other CAN errors are present.

### Conditions for Setting the DTC

#### P0115

The TCM receives no valid engine coolant temperature data from the ECM for 2 seconds.

#### P0120

The TCM receives no valid throttle position data from the ECM for 2 seconds.

#### P0826

The TCM detects an invalid voltage on the TAP Up/Down Signal Circuit for 5 seconds.

#### P2544

The ECM notifies the TCM that a torque reduction request has failed for 2 seconds.

#### P2637

The TCM receives an invalid engine torque value for 2 seconds.

### Action Taken When the DTC Sets

#### P0115

• | DTC P0115 is a Type C DTC.

• | The TCM uses 25°C (77°F) as a default engine coolant temperature value.

#### P0120

• | DTC P0120 is a Type B DTC.

• | The TCM uses the ECM default throttle position value for determining shift speeds.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

• | The TCM inhibits the TCC.

• | The TCM will default Accelerator Position data to 35 percent.

#### P0826

• | DTC P0826 is a Type C DTC.

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

#### P2544

• | DTC P2544 is a Type B DTC.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

#### P2637

• | DTC P2637 is a Type B DTC.

• | The TCM commands maximum line pressure.

• | The TCM freezes transmission adaptive functions.

• | The TCM inhibits Autograde braking and shift stabilization.

### Conditions for Clearing the DTC

• | DTCs P0120, P2544, and P2637 are Type B DTCs.

• | DTCs P0115, P0826 are Type C DTCs.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transmission General Description

#### 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

Transmission Control Module Scan Tool Information

### 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 repair.

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