U1900
CAN Communication Bus Fault — Receive Error
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Code U1900 is a Ford manufacturer-specific code indicating a CAN Communication Bus Fault with receive errors. This code is set when the PCM detects a communication failure between itself and other modules — specifically the instrument cluster, ABS control module, and trailer brake controller — on CAN bus circuits 1908 and 1909. Unlike generic U0xxx codes that point to a specific module being offline, U1900 indicates a broader problem with the communication bus itself.
One important thing to know about U1900 is that it's known to appear as a false or intermittent code. It can be triggered simply by connecting a scan tool to the OBD-II port while the ignition is on or the engine is running. If the code appeared during or immediately after a diagnostic scan, start by clearing it and seeing if it returns during normal driving. On Ford trucks, a commonly overlooked cause is an improperly installed aftermarket trailer brake controller that interferes with the CAN bus signals.
If the code returns after clearing, it indicates a genuine CAN bus communication problem that should be addressed within the week. The symptoms can range from minor dashboard warning lights to serious issues like 4WD system failure or a no-start condition, particularly on F-series trucks. A Ford-specific diagnostic approach is recommended, as the technician needs to isolate which module or wiring segment on circuits 1908/1909 is causing the receive errors. This typically involves checking wiring continuity, measuring CAN bus voltage levels, and isolating modules one at a time to find the source of the fault.
Severity
Symptoms
- •Check engine light illuminated
- •Multiple warning lights on dashboard (ABS, traction control, etc.)
- •4WD system may not engage on equipped vehicles
- •Vehicle may experience a no-start condition
- •Instrument cluster may behave erratically or lose readings
- •Intermittent electrical glitches across multiple systems
Likely Causes
Ford vehicles use CAN circuits 1908 and 1909 to connect the PCM, instrument cluster, ABS module, and trailer brake controller. Damaged, corroded, or shorted wiring on these circuits triggers U1900.
On Ford trucks with ABS brakes, an improperly installed aftermarket trailer brake controller can interfere with CAN bus communication on the shared circuits, causing receive errors.
U1900 is known to appear as a false code when a scan tool is connected while the ignition is on or engine is idling. If the code appeared during or after a scan, it may simply need to be cleared.
A failing control module on the shared CAN bus circuit can corrupt the bus signals and cause receive errors in other modules. This is more likely if U1900 keeps returning after clearing.
Insufficient voltage or a high-resistance ground connection can cause intermittent CAN bus communication errors, especially during high-load conditions like engine cranking.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Clear the code and monitor — may be a false trigger from a scan tool connection
- Check battery health and clean battery terminal and ground connections
- Inspect CAN bus wiring (circuits 1908/1909) for damage or corrosion
- Verify proper installation of any aftermarket trailer brake controller
- Repair or replace damaged CAN bus wiring and connectors
- Diagnose and replace any failing control module on the bus circuit