How to Diagnose EGR Valve Problems on a Paccar MX-13 (with SPN 2659)

How to Diagnose EGR Valve Problems on a Paccar MX-13 (with SPN 2659)

If your truck is showing SPN 2659 or struggling with low power and poor fuel economy, your EGR valve may be stuck, restricted, or misreporting flow. The Paccar MX-13 engine is notorious for EGR-related issues—and this blog walks you through exactly how to test and fix it using your diagnostic laptop and RP1210 adapter.

Common Symptoms of a Faulty EGR Valve

  • SPN 2659 FMI 0 (EGR low flow detected)

  • Black smoke under acceleration

  • Poor turbo response

  • Frequent regens or DPF clogging

  • Active derates or torque limiter engaged

Tools You’ll Need

  • Diesel diagnostic laptop with DAVIE4 or JPRO (with Paccar coverage)

  • RP1210 adapter (Nexiq USB-Link 2, Inline 7, etc.)

  • Basic hand tools if valve replacement is needed

Step-by-Step EGR Diagnosis (SPN 2659)

✅ Step 1: Connect and Scan for Codes

  • Launch your software and do a full module scan

  • Look for SPN 2659 FMI 0, 7, 8, or 18

  • Also note any codes like SPN 3251, 3719, or 3361 (EGR impact on DPF)

✅ Step 2: Compare Desired vs. Actual EGR Flow

Go to live data for EGR:

  • Watch the EGR flow rate (actual) vs. EGR flow rate (commanded)

  • If actual is consistently lower, the valve may be stuck, dirty, or restricted

💡 Tip: Use graphing view to see data during a 1,500–2,000 RPM rev test

✅ Step 3: Run the EGR Valve Test Routine

If your software allows:

  • Run the “EGR Valve Activation” test

  • Listen for clicking/movement

  • Watch for valve position % to change on screen

If there's no movement or data jump, your valve is stuck or the actuator is faulty.

✅ Step 4: Check for Sensor and Harness Damage

Many SPN 2659 cases are caused by:

  • Loose EGR position sensor wiring

  • Plugged EGR differential pressure tubes

  • Cracked EGR cooler causing false readings

What If the Valve Is Working But Flow Is Still Low?

If the EGR valve opens but flow remains too low:

  • The cooler may be plugged with soot

  • The intake manifold may be restricted

  • Or there's a post-turbo boost leak

You may need to:

  • Remove and clean the EGR cooler

  • Pressure test the intake and charge pipes

  • Replace the EGR valve if actuator response is weak or erratic

EGR Fault Code Quick Reference

SPN Code FMI Description Fix
2659 0 EGR flow too low Clean or replace valve, inspect cooler
2659 8 Abnormal signal Check sensor wiring
3251 18 DPF regen needed May be EGR-related
3361 2 EGR temp low EGR cooler issue

Wrap-Up:

SPN 2659 is a warning that your EGR system is failing to meet commanded flow. Ignoring it leads to derates, regen failures, and DPF overloads. The fix may be as simple as cleaning the valve—or may require a full cooler and sensor inspection.

Need the Right Tools?

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