Aisin 81-40LE - Automatic Transaxle

DTC U0401

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 (Component Tests and General Diagnostics).
* Repair any electrical circuit faults that were found. Refer to Wiring Repairs (Component Tests and General Diagnostics).
* Faulty ECM and/or TCM