|Trouble Code||Fault Location||Probable Cause|
|U0301||Software incompatibility - engine control module (ECM)|
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What Does Code U0301 Mean?
OBD II fault code U0301 is a generic trouble code that is defined as “Software Incompatibility With ECM/PCM”, and is set when the PCM (Powertrain Control Module) detects that inappropriate, incompatible, incorrect, or corrupted software had been used to perform or attempt a reprogramming event.
All modern PCMs require very specific software to be configured correctly. Apart from the software itself that controls/manages/monitors all aspects of the vehicle’s operation, a modern PCM must also be programmed with information that identifies the software version, as well as with information about the equipment (trim) level of the vehicle.
In most cases, modern PCMs are not programmed fully when they are first installed in new vehicles. The basic programming in a new PCM serves as a kind of shell into which the specific operating parameters of a given vehicle or model is programmed based on the trim level, equipment, and advanced safety systems that are fitted to that specific vehicle. For instance, one vehicle in a given model range may be equipped with stability control, while another model is equipped with stability and traction control, while yet another vehicle in the model range is equipped with both stability- and traction control, as well as adaptive cruise control.
Since the above example represents three very different software versions, each version is provided with a unique identifying number that is linked with the vehicle’s VIN when the PCM is programmed for the first time. Moreover, the software’s unique identifier is also linked to the software versions in use in other major control modules such as the TCM (Transmission Control Module) and BCM (Body Control Module), among others.
As a result, all the software in all control modules are directly related or linked both to the PCM and to each other via the link between the PCM’s software version identifier and the vehicle’s VIN. All subsequent official software updates, patches, fixes, and/or upgrades are therefore developed to be compatible with the original software in all of the vehicle’s control modules. While it is sometimes possible to install some software updates, patches, fixes, and/or upgrades into some vehicles with generic scan tools, these procedures typically require dealer-grade, professional-level scan tools to initiate and complete successfully, and then only under very specific conditions.
However, there are many reasons why software in one or more control modules can degrade or become corrupted, and while it is sometimes possible to reprogram affected control modules some conditions or failure modes require replacement of an affected control module. In almost all cases though, replacement and/or reprogramming of a control module requires that the module be integrated into the several serial communications systems in the vehicle, which in itself, can damage software in one or more control modules if specific instructions a not followed exactly.
In some cases though, it is easy to make the mistake of a) installing a replacement control module that is incompatible with one or more other existing control modules, or b), attempting to fix, patch, or upgrade the software in one or more control modules with software that is incompatible with existing software. If the PCM detects such an attempt, it will recognize that software incompatibilities exist within the vehicles’ overall control system topology, and it will set code U0301 as a result.
NOTE: It should be noted though that this code could, and does sometimes set as the result of brief, transient “glitches” in one or more control modules. These kinds of “glitches” can occur for any number of reasons, and while they do not typically affect any system(s) on the vehicle in meaningful ways, code U0301 or any of several closely related codes can remain in the vehicle’s fault memory as either “Pending”, or “Active” codes, even though the vehicle’s operation is not affected in any way. In some cases, such codes can only be cleared by performing a complete reprogramming of the PCM with the latest version of the correct software version with a dealer-grade scan tool under very specific conditions.
Where is the U0301 sensor located?
This image shows the inside of a typical automotive PCM, which strongly resembles the motherboard of a typical PC or laptop computer. Note that as with PCs and laptop computers, automotive PCMs contain no user-serviceable parts, and therefore, it is recommended that all programming and/or software incompatibility issues are resolved by suitably qualified personnel with access to all relevant technical knowledge and equipment.
What are the common causes of code U0301?
The possible causes of code U0301 are many, varied, and in some cases, unexplained if not downright mysterious. Nonetheless, some possible or probable causes could include one or more of the following-
- Programming and/or integration attempts performed with unsuitable scan tools
- Programming attempts with unsuitable, corrupted, incompatible, or outdated software
- Programming and/or integration attempts performed while system voltages are below a minimum allowable threshold
- Failure to follow prescribed reprogramming and/or integration steps
- One or more failed or failing control modules, including the PCM
- Corrupted software as the result of voltage spike caused by charging system faults, battery defects/malfunctions, or incorrect jump-starting procedures
- Corrupted software as the result of damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere on the vehicle
- Installation of one or more incorrect and/or unsuitable control modules
- Improper installation of some unauthorized aftermarket accessories such as some performance chips, or so-called patches to bypass some types of emission control devices
What are the symptoms of code U0301?
Symptoms of code U0301 could include one or more of the following, but note that in some cases, there may be no symptoms present except for the presence of code U0301-
- Stored trouble code, and in some cases, an illuminated MIL (CHECK ENGINE) light
- Depending on the application and the nature of the problem, several closely related codes, including U0300 and U0302 may be present along with U0301
- Depending on the vehicle and the nature of the problem, parasitic current draws ranging from slight and barely detectable, to severe may be present, but note that in cases where a parasitic current draws is present the vehicle may never enter sleep mode, which is almost always a required condition to diagnose parasitic current draw issues
- Depending on the vehicle and the nature of the problem, one or more electrical systems may behave erratically, or one or more systems may not function at all
- Vehicle may be immobilized
- A no-start condition may be present
- It may be impossible to gain entry into or to unlock vehicles with keyless entry systems
- In some cases where the problem is related to, or involves the TCM (Transmission Control Module) gearshifts may be harsh, erratic, or unpredictable