For 1990-2009 cars

### Circuit Description

Modules that are connected to the shared communication circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have pre-recorded information about what messages are needed to be exchanged on the serial data circuits for each virtual network. The messages are usually supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC U0401 TCM Received Invalid Data from ECM

### Conditions for Running the DTC

The ignition is ON or the engine is running.

### Conditions for Setting the DTC

The transmission control module (TCM) detects an invalid throttle position signal, engine speed signal and/or engine coolant temperature signal for more than 2 seconds.

### Action Taken When the DTC Sets

• | The TCM will store the DTC when a failure is detected on the first ignition cycle.

• | The TCM will illuminate the HOLD lamp.

• | The TCM can no longer determine the validity of any information it may or may not receive from the engine control module (ECM). Therefore the TCM substitutes default values for engine speed, throttle position, and other engine data signals.

• | Transmission operation will be reduced, affecting shift points, torque converter clutch operation, and other driveability concerns.

### Conditions for Clearing the DTC

• | The TCM turns OFF the hold lamp, when no further failures are detected on the next 3 ignition cycles.

• | The scan tool can clear the DTC from the TCM history.

• | The TCM clears the DTC from the TCM history after 40 consecutive warm-up cycles, when no further failures are detected.

### Diagnostic Aids

• | An intermittent malfunction may be caused by a fault in the electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections .

• | Repair any electrical circuit faults that were found. Refer to Wiring Repairs .

• | Faulty ECM and/or TCM

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Automatic Transmission Controls Schematics Connector End View Reference: Component Connector End Views
1 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Save the DTC and Freeze Frame information into the scan tool memory.
4. Perform the scan tool Clear DTC Information function for the transmission control module (TCM) and the engine control module (ECM).
5. Operate the vehicle for 1 minute or until the malfunction indicator lamp (MIL) illuminates.
6. Check the TCM for DTCs.

Is the MIL ON?

--

Go to Step 2

Go to Step 6

2 |

1. Select request DTC status from the Diagnostic Trouble Codes Information menu.
2. Request DTC by status.

Is DTC U0401 displayed?

--

Go to Step 3

Go to Step 6

3 |

1. Turn OFF the ignition.
2. Disconnect connector A from the TCM.
3. Turn the ignition ON, with the engine OFF.
4. Measure the resistance between terminal A17 of the TCM wiring connector and terminal K14 of the ECM wiring connector.
5. Measure the resistance between terminal A7 of the TCM wiring connector and terminal K15 of the ECM wiring connector.

Was the resistance the specified value for both circuits?

0 Ω

Go to Step 5

Go to Step 4

4 | Inspect for poor connections at the harness connector of the ECM and/or TCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you correct the condition? | -- | System OK | --
5 |

1. Turn the ignition ON, engine OFF.
2. Measure the voltage of terminal A17 of the TCM.
3. Measure the voltage of terminal A7 of the TCM.

Is the voltage within the values shown?

1.5-3 V

Go to Step 6

Go to Step 7

6 | Repair the terminals or the wiring connectors for intermittent failure, as necessary. Is the action complete? | -- | System OK | --
7 |

1. Replace the TCM. Refer to Transmission Control Module Replacement .
2. Turn the ignition OFF.
3. Turn the ignition ON.
4. Check if DTC U0401 is set.

Did the DTC reset?

--

Go to Step 8

Go to Step 9

8 | Replace the ECM. Refer to Control Module References . Did you complete the replacement? | -- | Go to Step 9 | --
9 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

--

Go to Step 1

System OK