Keep Aftertreatment Systems Performing Strong as Temperatures Drop

Aftertreatment systems on Class 8 trucks are often a source of common faults, and some faults tend to occur more frequently in the winter months due to colder temperatures and increased moisture. Proper precautions and proactive preventive maintenance can keep equipment functioning as temperatures drop.

“Use high-quality diesel exhaust fluid and ensure the diesel exhaust fluid (DEF) tank heaters are working properly to prevent issues in colder weather,” said Chris Hough, vice president of maintenance design and engineering for Penske Truck Leasing.

DEF is Temperature Sensitive

Diesel exhaust fluid, which is required by aftertreatment systems, is one of the most frequent causes of winter issues. It freezes at 12 degrees. Trucks have heaters, but frozen tanks and lines are a common source of delays. It is essential to confirm that tank heaters are functioning correctly before cold weather hits. Additionally, DEF contamination and crystallization caused by improper storage also increase in colder months, clogging pumps and injectors. Bulk DEF should be stored indoors or in heated tanks to ensure fluid remains usable.

Sensors and Exhaust Systems Can Struggle in the Cold

Moisture, corrosion and road salt can wreak havoc on nitrogen oxide (NOx) and exhaust temperature sensors, leading to false readings or failures. Exhaust system components also require close inspection, as cold weather can make gaskets and clamps brittle, raising the risk of leaks. Electrical and battery health are essential since many of the system’s heaters and pumps rely on strong, consistent power. Weak batteries or corroded connections can cause problems in low temperatures, and they should be checked during preventive maintenance. Once trucks are on the road, pre-trip inspections can help drivers spot potential issues early. They should also closely monitor dashboard alerts.

Idling Impacts DEF Regens

Diesel particulate filters (DPFs) collect particulates/soot that build up and must be burned off during a regeneration (regen). Regens can be performed while a truck is in motion, called a passive regen, or forcibly when the driver is stopped. Forced regens can take up to 45 minutes to complete, which can delay drivers. Trucks that spend long hours idling or making short runs often fail to reach the required temperatures for passive regens, which can lead to excessive soot buildup, frequent forced regen requests and, in some cases, derates. Incomplete regens are a common challenge with emissions systems. Managing idling and ensuring drivers complete forced regens as needed can help reduce failures and derates.

Earlier this year, the Environmental Protection Agency announced it will curb DEF shutdowns in new and existing trucks and called on original equipment manufacturers (OEMs) to update their software. “There haven't been enough details released to fully understand how this will be implemented. Some OEMs may be able to complete the update over the air, while others may not,” Hough said.

DPFs Must be Cleaned

In addition to cleanings done as part of the regen process, filters must be removed and cleaned as part of routine maintenance. Penske technicians track soot levels and, using both internal data and manufacturer guidelines, determine when a filter should be replaced. If longer engine warm-up times and increased idling prevent exhaust from reaching the high temperatures needed for effective regeneration, filters may need to be cleaned more often during colder months to avoid performance issues. Penske also operates four in-house DPF cleaning centers. By controlling the process in-house, Penske can clean filters faster and identify potential system or filter issues.

Hough added that good general maintenance habits, including fuel filter and air filter maintenance, can help prevent aftertreatment issues. Penske’s technicians have regular service intervals for key components within aftertreatment systems, and its diagnostic and analytics teams monitor vehicle data to identify and proactively address issues, improving uptime and vehicle reliability.

“Our main goal is to complete needed maintenance and updates without interrupting our customers' operations,” Hough said.