Diagnostic Aids

WARNING: This page is about a different variant/trim than selected.

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 Intermittent Conditions in Engine Controls 1.6L.
Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.
Faulty ECM and/or TCM

DTC U0401

Step	Action	Values	Yes	No
Schematic Reference: Automatic Transmission Controls Schematics Connector End View Reference: Connector End Views
1	Install a scan tool. Turn ON the ignition, with the engine OFF. Save the DTC and Freeze Frame information into the scan tool memory. Perform the scan tool Clear DTC Information function for the TCM and the ECM. Operate the vehicle for 1 minute or until the MIL illuminates. Check the TCM for DTCs. Is the Malfunction Indicator Lamp (MIL) On?	-	Go to Step 2	Repair the wiring connectors for intermittent failure
2	Select request DTC status from the Diagnostic Trouble Codes Information menu Request DTC by status Is DTC U0401 displayed?	-	Go to Step 3	Repair the wiring connectors for intermittent failure
3	Turn OFF the ignition. Disconnect connector A from the transmission control module (TCM). Turn the ignition ON, with the engine OFF. Measure the resistance between terminal A17 of the TCM wiring connector and terminal K14 of the ECM wiring connector. 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 in Wiring Systems. Did you correct the condition?	-	System OK	-
5	Turn the ignition ON, engine OFF. Measure the voltage of terminal A17 of the TCM. Measure the voltage of terminal A7 of the TCM. Is the voltage within the values shown?	1.5-3.0 V	Go to Step 6	Go to Step 7
6	Repair the terminals as necessary. Is the action complete?	-	System OK	-
7	Replace the TCM. Refer to Transmission Control Module (TCM) Replacement . Turn the ignition OFF. Turn the ignition ON. Check if DTC U0401 is set. Did the DTC reset?	-	Go to Step 8	Go to Step 9
8	Replace the ECM. Refer to Engine Control Module (ECM) Replacement in Engine Controls 1.6L. Did you complete the replacement?	-	Go to Step 9	-
9	Use the scan tool in order to clear the DTCs. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. Does the DTC reset?	-	Go to Step 1	System OK