3 Common Diagnostic Issues in Heavy-Duty Trucks and How to Address Them

Heavy-duty trucks are beasts of the road, designed for long hauls, carrying loads across vast distances. Yet, with their complex components and nonstop operational demands, these machines inevitably face mechanical challenges. Diagnosing these issues can be tricky, especially with modern diesel engines, advanced electronics, and after-treatment systems. Here, we dive into three common diagnostic issues in heavy-duty trucks and offer solutions to keep them running smoothly.

1. Engine Overheating

One of the most alarming sights for any truck driver is the temperature gauge creeping into the red. Overheating is a common but critical issue in heavy-duty trucks, often caused by issues within the cooling system, including the radiator, coolant levels, water pump, and fan clutch.

Low coolant levels are a primary reason for engine overheating. When coolant levels are low, the engine may not receive adequate cooling, which can cause it to overheat. Often, coolant leaks are the underlying issue, caused by damaged hoses or loose connections. Another common culprit is a faulty thermostat. The thermostat controls the coolant flow to the engine, and if it’s stuck in the closed position, coolant circulation stops, causing the engine temperature to rise. Additionally, the radiator can become blocked over time by debris and rust, reducing its efficiency in dissipating heat and leading to overheating.

Preventive Steps Against Overheating Engines

To address overheating, make checking coolant levels part of your routine maintenance, especially before long hauls. Look for visible signs of leaks under the truck or around the engine bay, as this can indicate damaged hoses or other issues. Radiator maintenance is also crucial. Cleaning the radiator regularly, using a soft brush to remove accumulated debris, helps prevent blockages while avoiding damage to its fins. If overheating issues persist, consider testing the thermostat and replacing it if necessary to ensure proper coolant flow and avoid unexpected engine shutdowns.

2. Transmission Malfunctions

Transmission issues in heavy-duty trucks have various symptoms of damage like slipping gears, hard shifting, or even grinding. They’re a complex mix of mechanical and electronic problems. Ignoring early signs can lead to costly repairs and significant downtime.

One of the most common causes of transmission malfunction is low or dirty transmission fluid. Transmission fluid lubricates the system, and when levels are low, it not only increases wear on gears but can also cause the transmission to overheat. Manual transmissions and a worn-out clutch may prevent proper gear engagement, while automatic transmissions can experience torque converter issues that make it difficult to engage the transmission properly. Regular transmission fluid checks and replacements according to the manufacturer’s recommendations are essential for maintaining optimal transmission function. 

Common Transmission Symptoms & Solutions

If you notice dark, burnt-smelling transmission fluid, a complete flush and replacement may be necessary. Additionally, use a diagnostic tool to scan for sensor errors in the transmission control module, as faulty sensors are a frequent cause of erratic shifting. It’s best to inspect and adjust the clutch as needed for manual transmissions as the wear and damage typically depend on the driver’s proficiency with manual vehicles. Replacing a faulty torque converter in automatic transmissions can help restore smooth, reliable gear engagement and prevent further damage.

3. After-Treatment System Failures

After-treatment systems like Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) have become integral in heavy-duty diesel engines for reducing emissions. However, these systems come with their diagnostic challenges and can lead to significant performance issues when they fail.

A major cause of after-treatment system failure is a clogged DPF. The DPF is designed to trap particulate matter from exhaust gases, but it can fill up over time, requiring a regeneration cycle to burn off the particles. If the regeneration process fails, the DPF remains clogged, which reduces engine performance. 

Additionally, the SCR system relies on a Diesel Exhaust Fluid (DEF) injector to introduce DEF into the exhaust stream, reducing nitrogen oxide emissions. A malfunctioning injector can lead to increased emissions and may trigger warning lights. In addition to these components, sensors are crucial to the after-treatment system’s functionality. If any of the multiple sensors fail, the system may receive inaccurate data and not operate as intended.

Clogged DPF & Aftertreatment Damage

When the DPF becomes clogged, initiating a manual regeneration cycle is often necessary, especially if automatic regeneration fails. During manual regeneration, ensure that the vehicle is driven at appropriate speeds, as short hauls can hinder the regeneration process. To maintain SCR function, inspect the DEF injector and supply lines, replacing clogged or damaged parts as needed. Using high-quality DEF can prevent contamination of the injector. Lastly, employ diagnostic tools to identify faulty sensors within the after-treatment system and replace them promptly. This will ensure that the system runs correctly, reducing false error codes and maintaining compliance with emission standards.

Preventive Maintenance Tips for Diagnostic Success

A little prevention goes a long way in heavy-duty truck diagnostics. Here are some tips to minimize these common issues:

• Regular Fluid Checks: This applies not only to coolant and transmission fluids but also engine oil, DEF, and other critical fluids.
• Schedule Periodic DPF Cleanings: DPF cleanings every few months or as recommended by the manufacturer can prevent clogs and increase longevity.
• Software Updates: Many diagnostic issues, especially those related to the transmission and after-treatment system, can be solved with an ECM (Engine Control Module) update. Keep software up-to-date to improve performance and troubleshoot potential issues before they become problems.

Optimal Performance with Regular Diagnostics

Texas Truck And Trailer Repair knows how to address common diagnostic issues and can keep heavy-duty trucks on the road to perform their best. Engine overheating, transmission malfunctions, and after-treatment system failures are among the most common issues. However, these challenges can be managed effectively with regular maintenance, quality components, and prompt diagnostics. By staying proactive with preventive maintenance and investing in regular diagnostic checks, you’ll not only reduce downtime but also extend the life of your truck. For more information about heavy-duty trucks, give our article on fuel efficiency a read.