U1900 code — how to fix error fast

You are probably aware of all the OBD2 codes that start with the mark “P” but the U1900 code is a pretty confusing, yet common code. Codes like this one often indicate communication errors or electrical issues on a large scale, so it’s no wonder that most drivers are unfamiliar with it.

To get to the bottom of the code and precisely solve this issue, you’ll need some insight into the U1900 code meaning and what you can do to repair and prevent it. We’ve assembled this guide with the professional insight of our team members dedicated to helping you out with the code’s diagnosis, solving it, and preventing it from recurring.

Why you can trust REREV’s OBD2 code advice: Our automotive expert researchers with experienced mechanics undertakes a thorough research methodology to deliver precise insights on OBD codes. Find out more about OBD2 codes research process..

What does the U1900 code mean?

The U1900 code is a diagnostic trouble code (DTC) that indicates a communication error between the vehicle control module (VCM) and the anti-theft control module (ATCM). It can cause a range of issues, from minor inconveniences to major safety concerns.

It’s crucial to understand this code and how to identify and fix it as it may help you save time and money, as well as keep your vehicle in top shape. Let’s move on to the main potential causes of this code since it may be affecting your car’s safety.

What causes the U1900 code?

This code can be caused by a number of things and they mostly all have to do with the lack of communication between the control module and the anti-theft system. However, there are some other potential reasons behind this code, such as the following:

Faulty wiring

Faulty wiring between the VCM and ATCM can lead to communication errors and trigger the U1900 code. This can occur due to damage to the wiring or connectors, or corrosion caused by exposure to moisture.

Malfunctioning modules

If either the VCM or ATCM is malfunctioning, it can cause communication errors and trigger the code. Malfunctioning modules can arise due to wear and tear, electrical issues, or other factors.

Dead battery

A dead battery can cause communication errors between the VCM and ATCM, leading to the U1900 code. This can occur due to a faulty battery or alternator, or because the battery has been drained by prolonged use of electronic devices or other factors.

Short circuit

Short circuits in the wiring between the VCM and ATCM can cause communication errors and trigger the code. This can happen due to damage to the wiring, exposure to moisture or other environmental factors, or other causes.

Which car models does the U1900 code affect the most?

The U1900 code can affect a wide range of car models, but some models are more susceptible to this code than others. Ford vehicles, for example, are known to be prone to this code due to issues with the PATS (Passive Anti-Theft System) module. We decided to take a closer look at the main complaints and reports regarding this code, and these models seem to be affected the most:

• Ford Focus: This error code can appear in a Focus due to a fault in the instrument cluster or a wiring issue related to the communication between the instrument cluster and the powertrain control module.
• Lincoln Town Car: Another car model that has been known to experience the code is the Lincoln Town Car. In this case, the error may be caused by a problem with the smart junction box, which is responsible for managing various electrical systems in the car.
• Mazda CX-7: The Mazda CX-7 may display this error message when there is an issue with the communication between the airbag control module and other control modules in the car.

How to diagnose the U1900 code

Diagnosing the U1900 code involves a series of steps, including identifying the symptoms, using diagnostic tools and equipment, and performing tests to determine the root cause of the issue. Here are some diagnostic methods that can be used:

Using an OBD2 scanner

Using a scan tool, a mechanic can retrieve the DTCs stored in the vehicle’s memory and identify the U1900 code. This can help narrow down the possible causes of the code and guide further diagnostic steps.

Visual inspection

A visual inspection of the wiring between the VCM and ATCM can help identify any obvious issues, such as damage, corrosion, or loose connections. This can help guide further diagnostic steps and identify potential fixes.

Circuit testing

Circuit testing involves using a multimeter to test the electrical circuits between the VCM and ATCM. This can help identify any issues with the wiring, such as short circuits or faulty connections.

How to fix the U1900 code

Fixing the U1900 code involves identifying the root cause of the issue and taking the appropriate steps to address it. Some potential fixes may include:

Repairing or replacing faulty wiring

If faulty wiring is identified as the root cause of the U1900 code, it may be necessary to repair or replace the damaged wiring or connectors. This can help restore communication between the VCM and ATCM and eliminate the code.

Replacing or reprogramming affected modules

If either the VCM or ATCM is identified as malfunctioning, it may be necessary to replace the affected module to eliminate the code. This can help restore proper communication between the modules and prevent further issues.

Recharging or replacing the battery

If a dead battery is identified as the root cause of the code, it may be necessary to recharge or replace the battery to restore proper communication between the modules.

How to Prevent the U1900 Code

Preventing this code is a great way of ensuring that you don’t have to deal with this sort of issue again in your car. Some of the preventive measures you can take with that goal include the following;

• Perform regular maintenance and check the modules
• Avoid using electronic devices too much
• Check the wiring and connections every once in a while

Properly storing the vehicle, such as in a garage or covered area, can also help prevent damage to the wiring and other components that can cause communication errors.

Our take

In the end, the U1900 code is a common issue that can affect a wide range of car models. Understanding what the code implies and how to deal with it is, therefore, crucial for each car owner that properly takes care of a vehicle.

We hope that this guide will help you in that sense and give you an easier time dealing with this code, as well as preventing it from happening again.