|Code||Fault Location||Probable Cause|
|U0401|| Invalid data received - engine control module (ECM) |
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|Wiring, Abnormal system voltages, Defective engine and driveability sensors|
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What Does Code U0401 Mean?
OBD II fault code U0401 is a generic code that is defined as “Invalid data received – engine control module (ECM), but sometimes as “Invalid Data Received from ECM (Engine/Electronic Control Module) /PCM (Powertrain Control Module) “A””, and is set when a communication fault occurs between two or more control modules.
Note that code U0401 is also sometimes further defined by a sub-code in this manner – U0401.XX. In these cases, the sub-code serves to define the particular system in which the fault is present. However, since not all manufacturers employ sub-codes, always refer to the manual for the affected application to determine the exact definition of code U0401 as it applies to that particular application.
In general terms though, all control modules on a modern application are interconnected via a highly complex web of wiring harnesses that is collectively known as the CAN (Controller Area Network) bus system. During normal vehicle operation, operational information and commands that affect all aspects of the vehicles’ operation are continually being exchanged between control modules, some of which are programmed to expect certain types of information from closely related modules.
In almost all cases, the PCM acts not only as a sort of clearing house for exchanged information, but it also “supervises” the exchange of information between control modules and should it detect a communication failure between two or more control modules for a period of time that exceeds a limit set by the manufacturer, it will set code U0401, and illuminate a warning light.
Where is the U0401 sensor located?
Due to the highly complex nature of modern CAN bus systems the fault can be located almost anywhere in the CAN bus system. However, in cases where there is no sub-code present, the fault is likely to involve wiring issues between the PCM and TCM (Transmission control Module), the PCM and the ABS control module, or the BCM (Body Control Module) and the airbags/seat belt control system.
However, depending on the application, other systems may be involved or implicated, so always refer to the manual for the application for details on the most likely fault locations, or the location of control modules that may have failed.
What are the common causes of code U0401?
Some common causes of code U0401 could include the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Abnormal system voltages
- On some applications, defective engine and driveability sensors can cause this code, or contribute to its setting. Note however that in these cases, defective sensors will be indicated by dedicated codes
- One or more defective control modules. Note that control module failure is rare, and the fault must be sought elsewhere before any control module is replaced
What are the symptoms of code U0401?
Although the most symptoms of code U0410 are largely make and model specific, some common symptoms could include the following-
- Varying degrees of power loss may be present
- Misfire-like symptoms may be present on some applications
- Transmission may enter a fail-safe or limp mode
- The ABS or other safety systems such as Traction Control and/ or Stability Control may be deactivated or unavailable
NOTE: Refer to the manual for the affected application for detailed information on the symptoms that are most likely to be present on that application.
What are common solutions to code U0401?
Common solutions could include the following-
- Replacement of sections of wiring
- Replacement of individual wiring harnesses
- Replacement of failed or failing control modules
NOTE: Replacing control modules may sometimes require reprogramming of the replacement module, or integration of the replacement module into the CAN bus system to allow the PCM to recognize the replacement module. Failure to perform the reprogramming or integration process may result in a recurrence of the problem, or an inability to clear the code.
How serious is code U0401?
Code U0401should be considered as serious since in some cases, the vehicle could enter a fail-safe or limp mode.
How safe is it to still drive the car with code U0401?
The presence of code U0401 could affect the safe operation of the vehicle, and especially if the ABS/Traction Control/Stability Control systems are affected.
How difficult is it to repair code U0401?
It is sometimes possible to diagnose and repair code U0401 on a DIY basis; however, in most cases, diagnosing code U0401 requires the use of advanced, make-and-model specific diagnostic equipment, as well as above average diagnostic skills. Note that cheap, generic code readers are generally not able to diagnose CAN bus, or control module related codes. If suitable diagnostic equipment is not available, refer the vehicle to the dealer or other specialist repair facility for professional diagnosis and repair.
NOTE: Non-professional mechanics should take note that if the cause of this code is not obvious, such as a disconnected ground strap or obviously burnt/damaged wiring, the better option is to refer the vehicle to the dealer or other specialist repair facility for professional diagnosis and repair.
What are the common mistakes when repairing code U0401?
Control modules that could include the PCM/TCM are often condemned and replaced out of hand when the most likely causes of this code are wiring issues or poor electrical connections.
One other common mistake many mechanics make is not investigating and resolving codes that accompany U0401. For instance, codes that indicate low system voltages are often ignored, even though these codes are often the direct cause of U0401.
How do you troubleshoot code U0401?
WARNING: The information provided in this section s intended for general informational purposes only, and should NOT be used in ANY diagnostic/repair procedure on ANY application without making proper reference to the manual for the affected application. Failure to make proper reference to the manual WILL lead to misdiagnoses, wasted time, and the unnecessary replacement of expensive parts and components that could include control modules.
Record all fault codes present, as well as all available freeze frame data. This information could be of use should an intermittent fault be diagnosed later on.
NOTE: If other codes are present, make a careful note of the order in which they were stored, since resolving codes that precede U0401 in this order will sometimes resolve U0401 as well. Nonetheless, do NOT make an attempt to diagnose U0401before referring to the manual to determine which system(s) are affected by code U0401.
Once the affected system(s) is identified, perform a thorough visual inspection of all associated wiring. Look for damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors. Make repairs or replace wiring as required.
NOTE: Ground straps and other wiring is often left disconnected after routine maintenance or repairs. Make sure that all ground straps and electrical connectors are connected/fully engaged before proceeding to Step 3.
If no visible damage is found, perform resistance, ground integrity, continuity, and reference voltage (where applicable) on all associated wiring, but be sure to follow the directions in the manual exactly to ensure the most accurate and reliable test results.
NOTE: Disconnect all wiring from all implicated control modules during this step to avoid damaging one or more control modules.
Compare all obtained readings with the values stated in the manual and make repairs or replace wiring/connectors as required to ensure that all electrical values fall within the ranges specified by the manufacturer.
Clear all codes after repairs are complete, and operate the vehicle for at least one complete drive cycle to see if any codes return.
If the fault persists but all electrical values/circuits check out, suspect a defective control module or control switch.
Note though that from this point on, testing and diagnostic procedures become entirely make and model specific that can vary from removing the complete wiring harness from the vehicle for detailed inspection or replacement, to replacing suspect control modules with known good units to verify the existence of a fault in various parts of the CAN bus system.
Thus, if a defective control module is suspected, and professional grade diagnostic equipment and reference data is not available, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair.
Codes Related to U0401
There are no known codes that are directly related to U0401 – “Invalid data received – engine control module (ECM)