OBD-II Code U1900 — What It Means & How to Fix It

What Does This Error Mean?

U1900 indicates a CAN communication bus fault — a problem with the data network that connects your vehicle's electronic modules to each other. This code appears when one module cannot send or receive data correctly on the network. Ford and Jaguar/Land Rover vehicles use U1900 frequently. Symptoms can include multiple warning lights, malfunctioning gauges, non-responsive infotainment, or intermittent electrical issues throughout the vehicle.

Affected Models

Ford F-150, Fusion, Focus, and Escape (very common)
Ford Transit and Transit Connect
Jaguar and Land Rover models
Lincoln vehicles

Common Causes

A failing or failed module on the network broadcasting corrupt data and jamming communication
Damaged CAN bus wiring — two wires (CAN High and CAN Low) that run throughout the vehicle
A corroded or damaged wiring connector on any module connected to the CAN network
Low battery voltage or a weak battery causing communication instability
An aftermarket module or device incorrectly connected to the CAN network

How to Fix It

Disconnect the negative battery terminal and wait 20 minutes. Reconnect and start the vehicle. Check if U1900 returns. A full system reset clears communication errors caused by temporary module lockups.

On Ford vehicles, a full reset requires disconnecting the battery for at least 15 minutes. Shorter times may not fully discharge the system capacitors.
Scan the vehicle with a multi-system scanner to identify all modules that have logged U1900 or related communication codes. Note which modules are reporting the fault — this helps locate which part of the network has the problem.

If all modules are reporting communication faults simultaneously, the problem is likely in the CAN bus wiring itself (both wires run throughout the vehicle) or in the gateway module.
Check the battery and charging system. A weak battery causes voltage fluctuations that disrupt CAN bus communication. Have the battery and alternator tested at any auto parts store for free.

Ford vehicles are particularly sensitive to battery condition. A 5-year-old battery that still starts the car may be weak enough to cause intermittent CAN communication faults.
Inspect wiring harnesses visible under the hood and under the dashboard for signs of damage. CAN bus wires are typically a twisted pair — one green/white wire and one green/orange wire on Ford vehicles. Any break in these wires can disrupt the entire network.

Rodent damage is a surprisingly common cause of CAN bus faults. Check anywhere a mouse or squirrel could nest in the engine bay.
If wiring and battery are both good, have a technician isolate which module is causing the communication fault by disconnecting modules one at a time while monitoring the network. This process is called 'network isolation' and requires a professional scanner.

This diagnostic process takes time and is best left to a technician. Randomly replacing modules is expensive and often unsuccessful.

When to Call a Professional

U1900 requires a professional scan tool that can perform CAN bus diagnostics. Diagnosis and network testing costs $100–$200 at most shops. Wiring repairs range from $100–$400 depending on the extent of damage. Module replacement costs $150–$900 depending on which module is identified as the problem.

Frequently Asked Questions

Why does my Ford show U1900 along with a dozen other codes?

U1900 on Ford vehicles often causes a cascade of other codes. When the CAN bus is disrupted, every module that depends on network data logs a fault. Do not try to address each code individually. Fix the underlying communication problem first — most of the other codes will clear on their own once the network is working correctly.

Can a bad ground cause U1900?

Yes — absolutely. The CAN bus network needs solid ground connections to function. A corroded or loose chassis ground can cause CAN communication faults across the entire network. Always check body ground straps and the battery negative cable connection to the body as part of U1900 diagnosis.

Is U1900 related to the check engine light?

Not always. U-series codes are network communication codes, not engine performance codes. The check engine light may or may not come on depending on whether the communication fault affects the powertrain control module. U1900 more commonly triggers the ABS, stability control, or other system warning lights.