U1900 Code: Meaning, Symptoms, Causes & Fix

Overview

Code U1900 indicates a fault in CAN Communication Bus Fault, typically within module-to-module CAN communication.

Symptoms

intermittent no-start or limp mode
module not responding in scan tool
feature communication timeout

Common causes

Module power/ground instability affecting can communication bus fault
Network termination or gateway fault
Connector pin damage/corrosion or harness stress near related components

How to diagnose U1900

Confirm U1900 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to can communication bus fault for obvious defects.
Check CAN high/low integrity, network termination resistance, and module wake-up status.
Check for related DTCs to identify the root-cause chain before replacing parts.
After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code U1900

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with U1900?

Most vehicles can be driven short-term with U1900, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

Repair obvious wiring/connector faults first to prevent repeat parts replacement.
Address the root fault mode (communication) in the can communication bus fault circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify U1900 remains cleared under the conditions that originally set the code.

Fix options

Stabilize voltage supply and module grounds.
Scan all modules for communication chain faults.
Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$260-$1300

Common mistakes when diagnosing U1900

Replacing parts without verifying voltage, ground, and signal integrity first.
Ignoring related stored/pending codes that indicate upstream faults.
Skipping post-repair verification drive cycle and readiness checks.

U1900 in common vehicles

U1900 appears across makes such as Mazda, Subaru, Lexus, Jeep. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes U1900?

U1900 is commonly set by communication faults affecting can communication bus fault.

How much does it cost to fix U1900?

For U1900, repair costs are typically $260-$1300 depending on exact root cause, labor rates, and part quality.

Can I clear U1900 without repair?

You can clear U1900 temporarily, but the code usually returns until the underlying fault is corrected.