The Wire Nobody Else Found

How Justin Mertz is defending the road across Cincinnati, one diagnosis at a time. 

The Peterbilt had been stuck in third gear for weeks. Two shops had already looked at it. The Allison was throwing codes, the TCM wasn't cooperating, and the dealer network was quoting a two-to-three-week wait. 

Then Justin Mertz got his hands on it. 

Four and a half hours of chasing wires, cutting zip ties, and pulling harness out of the loom at the transmission control module. One broken wire. A thirty-minute repair once he found it. Truck back on the road the same day. 

"If you get one wire wrong, guess what? It's not gonna work," Justin said. 

He'd applied the same methodology the day before on a Mercedes Sprinter whose leaking windshield had turned the SAM control unit into a green, corroded mess. Four shops had already touched it. Justin hardwired roughly 200 wires, one at a time, over two days. "Now it's fixed. No check engine lights, nothing. They're driving it today." 

Trusted by name

Justin supports Coltrain's Cincinnati market out of Florence, Kentucky, covering roughly 60 to 100 units across several customers. He and his teammate Tito were hand-picked for a high-trust assignment with a major national fleet account. The customer's response after the first rotation: send Justin and Tito back. Specifically. By name. 

"We've set the bar very high," Justin said. "And we're going to continue to set the bar higher." 

Justin came up running a garage, managing 100 to 150 owner-operators as both the lead mechanic and the business manager. Paperwork, billing, parts, customer relationships, all of it. That operational fluency shows up in the way he works a yard. 

"I come in, do my job, fix the stuff that needs fixing, make my customers happy," he said. "That's what I'm here for." 

A PM is not just an oil change 

Ask Justin what a proper preventative maintenance inspection looks like and you get a top-to-bottom tour at the speed of someone who's done it ten thousand times. 

"You look at the springs, the U-bolts, the frame, the airlines, the brake chambers, the brakes, wheel seals, oil pan. You look at everything under that truck. Driveline, U-joints, transmission. Lights, cab, interior, exterior. Top to bottom, inside and out." 

The PM isn't the headline work. It's where the trust is built, and where a trained eye catches the cracked brake drum before it explodes at a hard stop, or the weeping wheel seal before the bearings burn up and the axle fails. 

The math on missing it is where fleet managers quietly lose a quarter's budget. A wheel seal caught during a PM is a routine repair. Let it run dry, cook the bearings, scorch the hub, and suddenly you're calling in an axle specialist for a job that costs several times more, plus days of downtime instead of hours. 

"Call your local shop right now. Ask what the wait time is to get an International in. They're gonna tell you two to three weeks," Justin said. "I can normally fix it in two to three days depending on part availability." 

The shop comes to the truck 

Coltrain's operating model puts technicians directly in customer yards, equipped to execute PMs and follow-up repairs on-site. On one assignment, Justin found the customer had an underutilized Mercedes Xentry diagnostic computer on-site. He used it. The tool pointed him toward the problem area on the Sprinter; his experience found the actual failure. 

At the end of each day, Justin hands the on-site team a list of every truck completed and every part consumed, so inventory stays accurate. It's the kind of detail that doesn't show up on a repair order but keeps a customer's operation running clean. 

"None of the other contractors that have been in there could do that. It's not hard to write a number down on a piece of paper and give it to that guy." 

Building the bench 

Justin's teammate Brad came into the assignment as a trailer technician. Today he's a diesel technician, and he's the guy Justin trusts to cover Cincinnati when the job takes him out of state. 

"Brad said, I don't know as much about trucks as you, will you help me? I said, absolutely. You're willing to learn, I don't mind to help you." 

When Brad has a question from the field, he calls. They work it out on the phone. The customer gets the fix. 

"There's nothing we can't do as a team. Somebody over here might be better at something than somebody over here. But together, we're awesome. That's what makes us successful." 

The team behind the team 

That team-first thinking starts at the top of Justin's chain. His mobile service manager, Brennan Elkins, is the one who placed him on the national fleet assignment and backed him to run it his way. 

"Brennan gives us the freedom to do what we do best. If I need something, I call him and he makes it happen," Justin said. "He trusts his technicians to make the right calls for the customer. That kind of leadership is a big part of why this team performs the way it does." 

It's a philosophy that shows up across Coltrain's operating model. Technicians get the autonomy to solve problems on-site, the equipment to do the job right, and a leadership team that treats the field as the tip of the spear rather than the bottom of the org chart. 

Justin is also quick to point credit at the back office. 

"I'd like to make sure the team behind the scenes that takes care of all of our billing gets some recognition. They're responsible for a lot of this. A thank you goes a long way in our industry." 

Two people supporting a field team that submits multiple repair orders per technician per day, merging orders when multiple techs touch the same unit, making sure every part is accounted for. "They gotta cross all of our T's and dot all of our I's. They're not the face of the team, but they're responsible for a lot." 

That's the Coltrain model too. The technician in the yard is the visible half. The manager who trusts the call, and the operations team that keeps the paperwork clean, the parts accounted for, and the customer's billing accurate, is the half that makes the visible half possible. 

Four kids and a derby mower 

Off the clock, Justin is an outdoorsman, a demolition derby driver, and a proud dad. His middle daughter Caroline is his hunting, fishing, and derby partner. She has her own mower and runs events with him. His son James is, in Justin's words, "a miniature me." 

Ask him what keeps him motivated to crawl under a truck at seven o'clock on a Monday night in eighteen inches of snow and the answer is immediate. 

"My four kids. I want my kids to have a different life than I did when I was a kid. I'm not going to give my kids everything they want. But I will make sure they got everything they need. There's a big difference." 

The work is paying off. A new truck in the driveway. Bigger plans on the horizon. The derby is how he decompresses from Cincinnati bridge traffic. He is active in the community doing shows with Twisted Metal Motorsports, including competing at Kentucky Exposition Center's 18,750-capacity Freedom Hall at the Bourbon Beatdown in the spring on his custom-built derby mower (#213, Splatter) he's put real money into. If you're having a hard time picturing what that actually looks like, check out the 2025 mower class competition.

"You gotta have a little fun in your life and a way to relieve stress. I become a different person on that track." 

Defend the Road 

"Defend the Road means something different to everybody. To me, I want to make sure the trucks are safe to be on the road, and protect what goes on the road so that everybody is safe," Justin said. "My family travels the interstate just as well as everybody else's. That guy driving that truck might have kids. I want to make sure everybody gets to the goal line." 

That's the job. That's Justin Mertz. 

Coltrain Onsite Fleet Care keeps fleets moving with on-site preventative maintenance and repair, performed by technicians who've earned the work.

Looking to join a team that trusts its technicians? Explore careers at Coltrain. 

Got a truck that two shops couldn't fix? Get in touch.