This is the PACCAR U1820 CAN message of range diagnostic technical document for MX EPA truck engines. Published by PACCAR as part of their Rapido electronic service portal, this 2-page guide explains the diagnostic procedures, set conditions, and root-cause analysis for DTC U1820 activation in EPA 2004 and EPA 2013 compliant MX engines.
The U1820 fault code is a CAN communication diagnostic that triggers when a control module receives a message with signal values or status outside the manufacturer’s expected operational range, indicating either corrupted data transmission or a malfunction in the originating system.
Document details and specifications
| Brand | PACCAR |
| Model coverage | MX EPA engines (EPA 2004, EPA 2013) |
| System/Group | DTCs / MX Europe Engines |
| Publication number | U1820 |
| Year/Revision | 18 August 2017 |
| Pages | 2 |
| File size | 0.1 MB |
| Format | |
| Language | English |
Table of contents
- Set conditions
- Diagnostic condition
- Corresponding OBD readiness monitor
- Reset condition
- Repair verification
- Possible cause
- Additional information
What the PACCAR U1820 CAN message of range code means
The U1820 DTC is set when the receiving ECU detects that a CAN message has arrived correctly but the message content—the signal value or system status data—falls outside the expected valid range. The diagnostic runs continuously whenever the ignition is keyed on or the engine is running. Unlike many other DTCs, U1820 does not trigger an OBD readiness monitor and the code transitions to inactive status automatically after the diagnostic passes on the next test cycle.
Critically, the PACCAR U1820 CAN message of range code does not originate in the ECU that reports it. Instead, it is a secondary indicator of a malfunction in a different system that communicates with the reporting module via CAN bus. For example, if Sensor A fails and ECU 1 detects the open circuit, ECU 1 sends an empty or invalid CAN message to ECU 2. ECU 2 receives this message, interprets it as out-of-range data, and sets the U1820 code—even though the actual fault is in Sensor A connected to ECU 1.
Applies to these models
This PACCAR U1820 CAN message of range diagnostic applies to trucks equipped with MX EPA 2004 and MX EPA 2013 compliant engines communicating via CAN bus network architecture. Refer to PACCAR official website for full vehicle coverage and engine variant specifications.
Who needs this PACCAR U1820 CAN message of range manual
Diesel truck mechanics and workshop owners servicing PACCAR MX-powered vehicles need this guide to correctly diagnose and repair U1820 faults. Understanding that the U1820 CAN message out of range code points to a problem in a remote system—not the reporting ECU itself—prevents wasted diagnostic time and incorrect repairs.
Repair verification requires clearing all DTCs, test-driving the vehicle to meet set and diagnostic conditions, and confirming the code does not return. The full technical PDF is available in the DiagTechPro manuals library; a free account is required to download.
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