7 Common Aftertreatment System Problems in Freightliner 114SD Plus

7 Common Aftertreatment System Problems in Freightliner 114SD Plus

If you run a Freightliner 114SD Plus, you’re operating one of the most reliable vocational trucks in the industry. Yet every truck, including the 114SD Plus, encounters aftertreatment system issues. In Circleville, Ohio, where temperature swings from humid summers to frigid winters put extra strain on diesel emissions systems. Keeping your aftertreatment system healthy is a necessity. 

Let's walk through seven common aftertreatment system problems in Freightliner 114SD Plus trucks, and how to spot and fix them before they sideline your operation.

1. Frequent DPF Regenerations

If your truck constantly demands manual or forced DPF (Diesel Particulate Filter) regens, that's a big red flag. The DPF is designed to burn soot buildup through a natural regeneration cycle, but excessive or frequent forced regenerations usually indicate:

• Clogged or restricted DPF filter due to soot accumulation
• Faulty exhaust gas temperature (EGT) sensors
• Poor fuel combustion, leading to rapid soot buildup

In Circleville’s busy agricultural and industrial sectors, frequent idling or short trips can exacerbate this issue. The fix often involves cleaning or replacing the DPF and repairing underlying issues—like fuel system adjustments or sensor replacements—to restore normal regen cycles.

2. DEF Pump Failures

Your Freightliner 114SD Plus relies on Diesel Exhaust Fluid (DEF) to break down harmful NOx emissions. The DEF pump ensures precise fluid delivery, but failures are common and frustrating. Symptoms include sudden "Check Engine" lights, reduced engine power, or countdowns to derate mode.

DEF pump issues can occur due to:

• Internal pump corrosion from contaminated or aged DEF
• DEF crystallization caused by temperature extremes
• Electrical failures, like bad pump relays or wiring issues

Replacing or cleaning the DEF pump and ensuring quality DEF fluid can help prevent costly downtime.

3. DEF Injector Clogging 

The DEF injector sprays DEF fluid into the exhaust stream, creating the chemical reaction that reduces NOx emissions. But injector clogging happens frequently, especially when:

• Low-quality or expired DEF is used, leaving crystalline deposits
• The injector is exposed to freezing temperatures without proper DEF heater function
• Trucks experience frequent short trips or low-speed operations, causing buildup

Regular inspection, cleaning, and ensuring your DEF fluid meets ISO standards can help avoid clogged injectors and prevent emission system warnings.

4. Faulty NOx Sensors

NOx sensors measure nitrogen oxide levels in the exhaust, allowing the aftertreatment system to control emissions accurately. In Freightliner 114SD Plus trucks, NOx sensor failures can trigger derates, fault codes, or continuous check engine lights.

Causes include:

• Sensor contamination from oil, coolant leaks, or carbon buildup
• Excessive exhaust temperatures due to aggressive driving or exhaust restrictions
• Internal electronic failures from vibration or corrosion

Because NOx sensor faults mimic other aftertreatment issues, professional diagnostics are crucial to avoid unnecessary part replacements.

5. Exhaust Gas Recirculation (EGR) Valve Issues

The EGR valve recirculates exhaust gas back into the engine, lowering combustion temperatures and reducing NOx emissions. But over time, EGR valves become clogged with soot or fail to open and close properly.

Common signs include rough idle, decreased fuel economy, and frequent regenerations. Drivers around Circleville, OH, often see EGR issues from excessive idling or stop-and-go hauling, creating conditions for soot buildup.

Repair typically involves:

• Cleaning or replacing the EGR valve
• Checking the EGR cooler for leaks or restrictions
• Adjusting engine idle times or using fuel additives to reduce soot

6. SCR Catalyst Failure

Selective Catalytic Reduction (SCR) catalysts are vital for reducing NOx emissions. But these catalysts can degrade or fail over time, resulting in increased emissions and potential derates. Here are common causes:

• Excessive oil or coolant leaks contaminating the catalyst
• Repeated overheating due to prolonged heavy loads or incorrect exhaust temps
• Prolonged exposure to high sulfur fuels or poor-quality DEF fluid
• Age and mileage, leading to natural catalyst degradation

Catalyst replacement can be costly, but early detection of leaks or contamination can help avoid total SCR system failure.

7. Exhaust Leaks and Failed Clamps

An often-overlooked source of aftertreatment issues is exhaust leaks, usually from failed gaskets, cracked flex pipes, or broken exhaust clamps. These leaks disrupt the proper operation of the aftertreatment system, causing inaccurate sensor readings and increased soot buildup.

Symptoms include loud exhaust noise, soot streaks around joints, and mysterious regeneration failures. Exhaust leaks are more common in trucks that haul heavy loads or frequently encounter rough terrain, conditions common in Circleville’s agricultural and construction sectors.

Regular visual inspections of exhaust pipes, clamps, and gaskets can prevent these leaks from escalating into expensive repairs.

Keeping Aftertreatment Systems Healthy in Ohio’s Climate

Ohio’s seasonal extremes, humid summers, icy winters, put extra stress on your Freightliner’s aftertreatment components. Keeping your system healthy involves:

• Regularly scheduled aftertreatment system inspections and cleanings
• Using high-quality, certified DEF fluid and fuel additives
• Limiting unnecessary idling and performing proper warm-ups during cold starts
• Conducting emissions system diagnostics at the first sign of trouble

Preventive care goes a long way toward keeping your Freightliner 114SD Plus reliable year-round.

Keep Your Freightliner Running Clean

Aftertreatment systems in Freightliner 114SD Plus trucks are complex, but understanding common issues like frequent regens, DEF pump problems, sensor failures, and SCR catalyst degradation can save significant downtime and expenses. Staying ahead of these issues through regular inspections, quality DEF fluid, and proactive maintenance is the smartest strategy.

At Diesel Truck Repair in Circleville, OH, we specialize in diagnosing and solving aftertreatment issues for Freightliner trucks. We help fleets and owner-operators avoid downtime, stay compliant, and ensure their trucks run clean and powerful through every Ohio season. For more info about truck repairs, read our article on diesel electrical diagnostics. 

Don’t wait for aftertreatment problems to shut you down. Stay proactive, and keep your Freightliner 114SD Plus hauling strong.

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