In this series of troubleshooting postmortems, technicians will explain how they fixed a common issue on commercial vehicles.
The challenge
About two years ago, Lucas Coyle, master technician at TravelCenters of America in Gaston, Indiana, was assigned to diagnose an early model Freightliner Cascadia that was in derate mode. The Class 8 truck had been sidelined in the facility’s parking lot with an activated check engine light. In addition, the driver reported that the truck had been having issues completing Diesel Particulate Filter regenerations.
Using the shop’s Noregon JPRO diagnostic software, Coyle began looking into the cause of the problem by pulling all active and inactive fault codes. His initial investigation revealed several active aftertreatment system codes for high hydrocarbon absorption and high engine temperatures.
Following troubleshooting steps in repair information the facility could access as a Freightliner Service Point did not reveal any issue with the truck. Additional troubleshooting for multiple codes still found no apparent cause for the problem.
“I was not as proficient at aftertreatment issues and diagnosis at that point in time,” Coyle said. “I found myself going down a rabbit hole in the OEM’s service literature and it was difficult to focus on being patient about diagnostics.”
The Solution
It was then that Coyle turned to his training and remembered how the company’s manager of technical service once told him that the most important part of the combustion process is air. He had said that engine air filters are overlooked far too often during diagnosis, especially with aftertreatment issues.
Using that knowledge, Coyle determined that the engine air filter on this truck was clean, but the restriction was high after testing. He installed a new engine air filter and retested the inlet restriction—a quick step that eliminated the issue.
Using the JPRO tool, Coyle went on to monitor the temperatures of the engine and the aftertreatment system and noticed that the intake manifold temperature was higher than the turbo compressed air temperature.
His training told him that this unusual occurrence was incorrect, as the air should be cooled across the charge air cooler to the intake manifold. He removed the connector to the intake manifold temperature sensor and found that the connection was tight but the pins had become corroded. He then replaced the sensor and the connection to the sensor and retested.
After taking these steps, the truck completed the regeneration process and passed all verification for active codes. With all codes now inactive, the check engine light went out. The truck was no longer in derate mode and the customer was back on the road.
“One thing that has stuck with me from our training sessions is to not overlook the little things,” Coyle related. “I have learned that an initial overall inspection of vehicle health and operation will go a long way toward finding small issues that could affect the vehicle as a whole.
“I have since made a personal checklist for every truck that comes in the door,” Coyle added. “A quick look at four key areas—Coolant, Oil, Air and Exhaust—has made repairs easier and faster, which is beneficial to me, and to the customer who does not have to spend unnecessary time and money on a diagnosis of a truck that that may need something simple.”
About the technician
Lucas Coyle began his career at TravelCenters of America six years ago as a lube and tire technician. He was 18 years old at the time. Over four years, he attended six one-week classes at the company’s internal training facility. Within his first three years he earned ASE Master Certification for Medium- and Heavy-Duty vehicles, and recently achieved ASE L2 Advanced Level Specialist certification.
Today, Coyle is one of ten technicians in the Gaston, Indiana, TA Petro shop, a five-bay facility that operates 24/7 servicing mainly all makes of over the road Class 8 trucks.
“Once I became familiar with the company and all of the training that was available to me I knew I wanted to make a career out of this field,” Coyle stated. “Now I do some of everything in terms of service and I have regular customers that come to me for Preventive Maintenance and repairs. My favorite issues to work on are check engine light and air system repair challenges.”
Coyle competed in the 2021 TMC SuperTech Competition, earning top spot in the Transmission and Lighting stations, finishing in 8th place overall.
