Diagnostic nightmares and horror stories from the shop

Brandon Harden, field service technician for Cox Automotive Mobility, was no stranger to fuel filter changes. An experienced technician with 10 years of repairs under his belt, he had no reason to be concerned when a 2022 Mack Anthemcame into the shop with a brand-new Mack MP7 engine. All seemed well, until Harden went to test the vehicle, and instead of a smooth engine’s purr, an unholy noise filled his ears.

“There's this brand-new, $100,000-and-some truck that came in to get its fuel filter changed, I changed it, and now the truck doesn't run after—it just made a horrible sound,” Harden recalled.

For the next several hours, Harden and his fellow technicians looked over the vehicle, trying everything from cranking the engine, to shooting it with ether, putting fuel in the filters, and priming the system. But they worked on with dogged determination.

“There are parts changers and then there are technicians,” Harden said. “Parts changers just throw parts at it until they figure out what's wrong. A technician will go through and find exactly what's wrong. If there's something wrong, why did it go wrong? And then we'll fix why it went wrong and what went wrong.”

That's what Harden and his fellows were determined to do for this monster of a truck. Their efforts could have gone on longer until one of Harden’s peers was examining a new fuel filter and Harden noticed that it had something that the one currently in the truck did not: a small, plastic nozzle inside the filter itself.

Willing to give anything a shot to restore the truck, Harden carefully filled the filter up, switched out the filter he’d originally replaced, and within seconds the vehicle was working again.

It turned out that while Harden had been replacing the filter, he’d accidentally broken off the nozzle, which had then gone through the fuel system with little harm but was still critical to the truck’s functionality.

“We had just spent two and a half hours trying to get this truck to start, thinking that it had just blown up, when really all it was was I broke a plastic nozzle off the fuel filter,” Harden said. “That definitely will be the last time [that] happens to me.”

But the incident didn’t come without educational value.

“If I was to go back and tell myself [some advice], it would just be slow down, be a little more careful,” Harden explained. “Just look at things when you run into a problem.”

The curse of the vampiric batteries

Curtis Hart, a technician with Transervice who’d spent over 15 years as a diagnostician, once encountered an entire group of vehicles that would suddenly break down.

Hart’s location once received 12 new 2020 Freightliner Cascadias, but within a month, their office began getting multiple breakdown calls. With clock regularity, the trucks would refuse to start on Monday morning after a weekend in the lot. Once vendors arrived at the scene, they would be able to jump-start the vehicles with no problem, but the following Monday, the office phones would begin to ring again.

When tasked with diagnosing the chronically-dead trucks, Hart began by checking the vehicles with their electronic logging device (ELD) system.

“Every Monday, the ELD system would show that the [trucks’] ignition was in the 'on' position,” Hart said. “[It was] hard to believe that 12 drivers would be leaving their keys in the truck in the on position, but that’s what the data was showing.”

Transervice had their dealer check the vehicles, but they couldn’t recreate the phenomenon. Instead, when the trucks next came in for scheduled maintenance, Hart ran through his basic tests, including those for the battery, alternator, key ignition switch, and ignition relay. He ran a parasitic draw test as well, at which point he made a key discovery while examining the accessory switches on the dashboard:

“When the trailer aux power switch was turned on, the cab courtesy lights would turn on for 10 seconds, which was 'waking' a module,” Hart described. “In turn, it would increase amperage draw, which was evident watching my recordable meter. The lights would shut off after the 10seconds; however, the draw on the batteries would not drop to a ‘safe’ load until the trailer aux switch was turned back off.”

Finding this suspicious, Hart went to check the truck’s fuse box, where he found that the trailer aux circuit was wired to a panel that shared a truck cavity with the ELD and SmartDrive systems. With a little more detective work, he found that the dealer had spliced the trailer aux circuit.

“When the aux switch was in the ‘on’ position, it was back-feeding the fuse panel, which was then providing 12V to the ignition circuits of the ELD and SmartDrive systems,” Hart said. “I made the repair by utilizing a standard relay and wiring it into the circuit, separating key ignition from the aux circuit.”

This repair was disseminated to Transervice locations across the country, allowing all of the defunct Cascadia vehicles to be fixed at once.

Night of the (un)living truck

Meanwhile, another technician in another state was also dealing with undead asset problems. Jared Kennedy, a technician of five years for UPS, found himself facing a 2014 Morgan Olson Freightliner with a GM 6.0L engine that would run for a short period before giving up the ghost.

“It would go out for a few days, then come back in with a no crank, no start, no comms on the dash as well,” Kennedy said.

After some examination, he found that the vehicle was losing power to its engine control module (ECM) relay, despite the battery box and the fuse block functioning as normal. With those two culprits ruled out, Kennedy moved to the harness. The splices were sealed and seemed fine, but upon using a thermal camera, he discovered that one of the wires had a hot spot.

“I cut it open and found one of the wires hadn't been properly captured by the crimp and was only being held in contact by the heat shrink,” Kennedy explained. “Once I redid the splice, that car ran fine with no more issues.”

The wailing washer pump

Even when a truck is technically working fine, sometimes it may be haunted by the loss of a single element that keeps it from the road. Michael Johnson, a senior technician for Cox Automotive Fleet Services, found such a ghost in the windshield-washer pump of a 2016 Cascadia Freightliner M2.

In all his 27 years on the shop floor, Johnson had not seen a problem of this ilk. Although the washer pump and the wipers used the same module signal, the wipers were operational while the pump was not. Instead, the dash-light item stubbornly refused to function despite the efforts of three different technicians, each who made three different journeys out to examine the vehicle. If Johnson were to fail, the vehicle would be sent to the dealer.

“We had a guy who replaced the pump itself, we had a guy who replaced the whole reservoir with the pump, we had one guy replace the actual switch in the cab that actuates it, and none of that worked,” Johnson said. “We checked fuses, checked wires, [before] I finally had time to actually get into it and troubleshoot it.”

To begin, Johnson ran a continuity test, finding that one particular wire was grounded, creating continuity where there shouldn’t be. Using his multimeter, Johnson triangulated the voltage irregularity by performing a wiggle test, checking each wire until his tool identified which one lacked the power delivery needed. It was painstaking work, with Johnson spending four hours unraveling the harness, wire-by-wire, to discover the culprit for the fault.

“What I ended up finding was that three wires, one of which operated the pump motor, were actually arcing out on the frame of the truck,” Johnson remembered. “So, I was able to repair the wires, and everything [was] working fine.”

From discovery to repair, Johnson spent four hours with the vehicle, in the end finding that the easiest solution, albeit not the least labor-intensive, guided him to a solution.

“There's that saying, ‘Keep it simple, stupid,’” Johnson recalled ruefully. “We replaced three parts on that truck that didn't have to be replaced because of wires. If we had done the basic checks and known how to use them to locate the problem, it certainly could have saved the customer the money and saved us some time.”

The loping werewolf engine

Although beasts of all kinds roam the land, none want to come across one in their shop. Unfortunately, that’s just what Talon Thomas, a Noregon Systems product management technical engineer and former diesel technician, found in a 1995 Chevy 1500 pickup.

The owner of the vehicle, who was a friend of the shop’s owner, had recently replaced his own engine with a brand-new 5.7L V8 crate engine from General Motors. But despite the novelty of the engine, something was not quite right.

“When the vehicle would sit there and warm up for a minute, it would run fine,” Thomas said. “And then, it would start to lope at idle. It would sit there and hunt. The RPM would go from normal to low and then rise back up to normal and then drop back down to low. And it would do this constantly once the fuel system was in closed-loop operation.”

Mystified at how an otherwise-perfect vehicle had wolf-like tendencies, Thomas and his peers spent two hours, then four, then six looking for pattern failures and faults, but nothing seemed amiss. Eventually, the customer took the vehicle home, and on occasion, he’d bring it back for the shop to look at. They tracked their work, spreading their efforts across two weeks and sometimes even bringing the vehicle home with them to examine.

“We tested everything we possibly could,” Thomas remembered. “Everything from a mechanical perspective looked great. Everything from an electronic perspective looked great. There's nothing that was out of spec. But the engine control module was seeing something that it didn't like.”