Top 5 Common Fault Codes in Commercial Trucks and How to Fix Them

Introduction

Fleet managers and truck technicians encounter the same fault codes repeatedly. Here are the top 5 most common ones and how to address them.

1. P0401 – EGR Flow Insufficient

The Exhaust Gas Recirculation valve is often clogged with carbon deposits. Clean or replace the EGR valve and retest.

2. P1093 – Fuel Rail Pressure Low

This often indicates a failing high-pressure fuel pump or clogged fuel filter. Check fuel pressure with a diagnostic tool before replacing parts.

3. P0087 – Fuel System Pressure Too Low

Common on high-mileage trucks. Inspect the fuel pump, pressure regulator, and injectors.

4. P2263 – Turbocharger Boost System Performance

Check the turbo actuator, wastegate, and intercooler hoses for leaks. Use live data to monitor boost pressure.

5. SPN 3031 / FMI 16 – DEF Quality Poor

The Diesel Exhaust Fluid (DEF) concentration is out of range. Drain and refill with certified DEF fluid, then reset the SCR system via your diagnostic tool.