DTC Trigger

The DTC sets when the PSCM receives invalid data from the PCM. The data is likely invalid due to PCM internal errors, damaged or inoperative sensors or components the PCM uses to gather vehicle data. The invalid data DTC is not set due to the PSCM, PSCM wiring or connectors. Consult the DTC index for additional information if needed.

Pinpoint Test Purpose 

To verify the presence of DTC U0401 and identify the correct Service Information for diagnosing the DTC concern.

1. AS1: CHECK PSCM DTC 
   • Ignition ON, engine running.

   Carry out the PSCM self-test.

   • Is DTC U0401:xx currently present and active in the PSCM? 

     Yes	No
     Go to  AS2.	If the PSCM does NOT list DTC U0401 Invalid Data Received from the ECM/PCM, DISCONTINUE this test and REFER to the DTC Chart for diagnostic direction.

2. AS2: CHECK THE VEHICLE BATTERY AND CHARGING SYSTEM VOLTAGE 
   • Ignition ON, engine OFF.
   • Refer to the Charging System General Information article and carry out Pinpoint Test A: Battery Condition Test (battery state of charge).
   • Did the battery pass the condition test (battery state of charge)? 

     Yes	No
     Go to  AS3.	INSTALL a new 12-volt battery. REFER to the Battery, Mounting and Cables article. Go to  AS3.

3. AS3: RECHECK THE PSCM DTC 
   • Ignition ON, engine OFF.
   • Clear the PSCM DTCs.
   • Ignition OFF.
   • Ignition ON, engine running.

   Carry out the PSCM self-test.

   • Is DTC U0401:xx currently present and active in the PSCM? 

     Yes	No
     DIAGNOSE the PCM concern. REFER to the Engine Controls article or the Electronic Engine Controls article.	The concern is not present at this time and may have been set due to a low battery state of charge. The test is complete, no further action is required.