This is the official 2013 PACCAR MX P0408 EGR difference diagnostic service manual, published by PACCAR for technicians troubleshooting exhaust gas recirculation system faults on EPA 2013–compliant MX engines. The document provides complete fault code definitions, component descriptions, electrical diagrams, and step-by-step diagnostic procedures to isolate and repair P0408 voltage and short circuit conditions on ECU pin D420 C80.
P0408 is triggered when the ECU detects EGR pressure difference sensor output voltage exceeding 4.81 V, indicating either a faulty sensor, wiring short circuit to the 5 V supply, or internal ECU failure. This manual covers the sensor location, operating temperature limits (125°C maximum with coolant cooling), and the dual internal pressure sensors that measure differential flow through the EGR venturi.
Document details and specifications — PACCAR MX P0408
| Brand | PACCAR |
| Model coverage | MX Engines (EPA 2013) |
| System/Group | DTCs / EGR Pressure Difference Sensor |
| Publication number | Not specified |
| Year/Revision | 2013 |
| Pages | 4 |
| File size | 0.4 MB |
| Format | |
| Language | English |
Table of contents
- Code P0408 fault description and diagnostic information
- Component description and location – EGR pressure difference sensor with dual internal sensors
- Diagnostic condition status and fault code set/reset criteria
- Electrical diagrams and wiring harness connector pinouts (D420, F751)
- Technical data and component wiring check procedures for ECU D420
- Possible causes: faulty sensor, short circuit to supply, cross-pin shorts
- Step-by-step diagnostic troubleshooting tree (Steps 1–5: visual inspection through PCI verification)
- Verification drive cycle procedure for repair validation
Applies to these models
This PACCAR MX P0408 EGR diagnostic manual applies exclusively to PACCAR MX engines built to 2013 EPA emissions standards. The procedures cover the pressure difference sensor circuit on connector F751 (pins 1, 2, 3) interfacing with ECU D420 (pins C35, C58, C80). For authoritative PACCAR engine and emissions documentation, visit PACCAR official.
Who needs this PACCAR MX P0408 EGR manual
Diesel mechanics and workshop owners diagnosing active P0408 faults on PACCAR MX–powered trucks need this manual to isolate sensor failures from electrical shorts and ECU pin damage. The manual is essential for technicians using DAVIE diagnostic software and breakout harnesses to perform safe, non-destructive electrical testing.
The full MX P0408 EGR diagnostic PDF is available in the DiagTechPro manuals library. A free account is required to download.
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