This EPA CAN troubleshooting U1781B guide provides systematic fault isolation procedures for CAN network-related diagnostic trouble codes on PACCAR MX engines compliant with EPA 2004 and EPA 2013 emissions standards. Published by PACCAR and extracted from the Rapido technical portal, this document is essential for workshop technicians diagnosing U-code DTCs on MX-series truck engines.
The guide emphasizes that inactive CAN-related DTCs are often caused by temporary network overload or voltage dips during engine startup and should not be routinely troubleshot. However, active CAN faults require methodical investigation following the four-step troubleshooting sequence outlined in this manual.
Document details and specifications — EPA CAN troubleshooting
| Brand | PACCAR |
| Model coverage | MX EPA13, MX EPA04 engines |
| System/Group | DTCs / MX Europe Engines (EPA 2004) |
| Publication no. | U1781B |
| Year/Revision | 18 August 2017 |
| Pages | 7 |
| File size | 0.1 MB |
| Format | |
| Language | English |
Table of contents
- General troubleshooting – CAN
- Step 1 – Investigate related DTCs (P-code and aftermarket device checks)
- Step 2 – CAN-related component and power checks (visual inspection and electrical testing)
- Step 3 – Isolate faulty CAN network or component (V-CAN, E-CAN, and A-CAN termination resistance testing)
- Step 4 – Clear CAN-related DTCs
Applies to these models
This EPA CAN troubleshooting U1781B guide applies to PACCAR MX-series engines manufactured to EPA 2004 and EPA 2013 emissions standards, covering CAN network diagnostics on PCI ECU, EAS-3 ECU, and associated aftertreatment components including VTG turbocharger actuators and NOx sensors. For complete technical specifications and updates, visit PACCAR official website.
Who needs this CAN troubleshooting U1781B guide
Heavy-duty truck mechanics and workshop managers servicing PACCAR MX-powered vehicles require this CAN troubleshooting guide to diagnose and resolve network communication faults. Technicians performing electrical diagnostics on MX engines will find the resistance testing values, connector pin locations, and step-by-step isolation procedures invaluable for efficient fault resolution.
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