Light Duty: Maintaining All-Wheel and Four-Wheel Drive

Whether your fleet is built for rocky off-roads or slick winter highways, AWDs and 4WDs both need TLC.

“What’s really nice about a full-time four-wheel drive system is that what allows it to do that is the center differential,” he says. “Unfortunately in a real severe heavy-duty situation, that’s the weak link, because now you have a third differential in the link that could possibly fail if you’re carrying a lot of capacity; where in your typical four-wheel drive system, the center differential is replaced by a transfer case, which is a much more heavy-duty gearbox.”


Williams says there is not too much extra for technicians to do when troubleshooting and maintaining 4WD systems.

“It’s just a little bit more when you’re doing your (preventative maintenance), that you’re checking the front axle differential level, you’re looking at the u-joints, you’re looking for leaks,” he says. “So you spend a few more minutes looking at the front end, but the maintenance isn’t much more different on them.”

Thompson says the biggest maintenance concern is—surprise—diagnostics.

“(Technicians) need to understand what circuits to look at and when,” he says. “We try to establish the fault codes in the controlling module so that if the ‘service four-wheel drive’ light comes up on the dash, we try to narrow it down for the techs. The quick response sometimes is to replace the module rather than find out why it set a fault.”

“Diagnosing these electronic systems does demand a more adequate diagnostic procedure to be written down for them to follow,” Thompson says. “Back in the days, they could just wing it or it was in the capacity of most technicians to just look at the mechanical linkage and say, ‘Oh, this just isn’t adjusted right’ But now the demand is more on us to get them the information and documentation they need to thoroughly analyze a faulty system.”

Toyota’s Kwong says since they did away with manual-locking hubs, everything is now automatic.

“The only thing you need to do every 30,000 miles is inspect and replace, if necessary, the transfer case and differential fluid, unless you’re doing some really heavy-duty stuff on a regular basis,” he says.

Knowledge of electronics and sensors is very important, says Cavanaugh.

“If they’ve got a broken part and they don’t really understand that it’s broken, they can look at a sensor all day and may not understand that it’s not working properly,” he says. “Just replacing things doesn’t necessarily do it. If you have a good technician, he should be able to read and understand that the actual sensor is not functioning if he follows his checklist, and being able to do that through an OED2 connector and actually going in and reading what’s going on and analyzing; that would help him out a lot and save him a lot of time.”


All-wheel and four-wheel drive vehicles are a necessity for fleets in some regions and conditions, but first you need to make sure you’re not wasting money buying expensive systems your drivers may want but you don’t need.

And since much of the maintenance these days is electronics-based, if you make sure your technicians are up to speed on their diagnostics, your vehicles will have much smoother sailing ahead, no matter how rough the roads they travel.

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