Many truck parts fail earlier than expected, fleet managers say

Failing truck parts got you down? You’re not alone, and statistics prove it.

A recent survey of fleet managers indicates that parts common to modern heavy-duty trucks – especially sensors – break sooner than expected, taking trucks out of service and costing time and money to replace.

Sensors in exhaust emission control systems appear to be the weakest items, lasting less than half as long as managers expected. On the other hand, some parts – starter motors and pads and rotors of disc brakes – lasted somewhat longer than expected.

The survey was done in April of this year by the Technology & Maintenance Council of the American Trucking Associations, and it included responses from eight for-hire and private fleet members of TMC. That was a small sample, TMC’s report said, so “one must caution against drawing too many conclusions based on the data collected.” But the results seemed to mirror word-of-mouth stories of early failures, especially of exhaust-system sensors.

The accompanying charts list the 14 types of components that fleet managers commented on and the percentages of expected life realized. Expectation figures are what managers said they were, TMC explained. The stated percentages and mileages were averaged among all responses.

The worst part named in the survey was the DEF quality sensor that continually analyzes diesel-exhaust fluid, which chemically breaks down exhaust gas into harmless molecules. The sensor detects when the special fluid is diluted or replaced by plain water or some other substance that’s cheaper than DEF, and it reduces engine power or shuts down the engine. This sensor attained only 38.64% of expected life: 161,667 miles vs. 418,333 miles managers thought they should get.

Sensors that measure particulate matter, or PM, and nitrogen oxides, or NOx, also failed earlier than expected, at 40% and 44.23% respectively, the survey found. Those equate to 266,667 miles attained vs. 666,667 miles expected for PM sensors and to 191,667 attained vs. 433,333 expected for NOx sensors.

Another category of disappointment was automated manual transmission parts: Clutches lasted 57.49% of expected service life, and clutch actuators needed replacement at 73% of their expected lives. Shifter controls – the stalk mounted to a truck’s steering column – failed at 58.49% of expected life. However, these items lasted two to three times longer in miles than the troublesome exhaust system sensors, the survey found.

Some of the comparatively fragile parts are expensive, and prices vary among the types and brands of parts. One builder’s DEF quality sensor, for example, ranges from $300 to $400 to replace. If it incorporates a fluid-level probe, as does another maker’s, the cost is $1,200 to $1,500 per unit.

Happier news involved the air disc brake parts: 12.5% greater than expected life for pads and 23% more than expected life for rotors. These results jibe with claims made by manufacturers who have long touted the maintenance benefits of disc brakes compared to traditional drum brakes. And starter motors lasted 37% longer than managers anticipated. Crank’er over! LL