Written by the Motorplex Team
Offering fleet repairs in Auburn and Spokane, WA
The gauge says you still have half a tank, but you’ve really been putting on the miles, and it should be near empty. A faulty fuel gauge can cause serious problems and affect route planning, productivity, and safety. If you don’t know how much fuel you have, it’s really easy to run out in the most inconvenient places!
Recently, a 2017 Kenworth T680 came into our fleet service shop in Auburn, WA, with a fuel gauge issue. It clearly wasn’t reading correctly and needed to be fixed. In this article, we’ll share how I handled this relatively simple fix and what can cause a faulty fuel gauge.
Starting With the Basics
Fuel gauge issues can start in several places, so our technician began by testing the most common failure points before pulling anything apart. The fuel level sensor and harness were checked first. Both tested fine, and the voltage at the circuit was within specification. That ruled out wiring damage, poor connections, and sensor failure.
So, the next step was to test the gauge itself. The fuel level sensor was removed from the tank, and the gauge was checked manually by moving the float to simulate an empty, partially full and full tank. Then they could check the reading and see if it was a float issue.
At empty, the gauge dropped about one-eighth below empty. At full, it only read seven-eighths full. That offset confirmed the problem was with the gauge’s instrument cluster. It was an eighth of a tank off, which might not seem like that much, but when you have a 120-gallon tank, that’s a lot of fuel!
Instrument Cluster Was the Problem
In this case, testing confirmed the fuel gauge was faulty. The remaining question was whether the gauge could be serviced individually or if it was integrated into the instrument cluster. On many trucks, gauges are part of a larger cluster assembly, which requires specialized repair rather than simple replacement. Our technician pulled out the dash and cluster so we could take a closer look.
The decision was made to schedule a rebuild of the instrument cluster with Tacoma Speedo, a trusted regional specialist. In addition, we checked the fuel level sender harness overlay to ensure it was sending the correct fuel level signals from the tank to the dashboard gauge. Once we got the cluster back, we were able to reinstall everything and call the job done.
What Can Cause a Fuel Gauge to Read Incorrectly?
Fuel gauge problems are often blamed on the sending unit, but that is only one possible cause. In heavy-duty trucks like the Kenworth T680, inaccurate readings can be caused by:
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- Faulty fuel level sensors
- Damaged or corroded wiring
- Voltage supply issues
- Calibration problems within the instrument cluster itself.
In some cases, aftermarket wiring repairs or harness overlays can impact gauge readings. Or, internal wear inside the gauge causes it to drift over time. Instrument clusters are exposed to constant vibration, temperature changes, and electrical load, which can gradually affect the accuracy of a fuel gauge even when the truck is otherwise running well.
Even If It's a Little Off, It's a Big Problem
An inaccurate fuel gauge may seem minor, especially when it’s only off by an eighth or sixteenth of a tank, but it can create real operational risks. Drivers may run out of fuel unexpectedly, idle excessively to avoid shutting down, or waste time making unnecessary stops. Over time, those small issues add up to higher costs and lost productivity.
From a maintenance perspective, unresolved gauge issues can also mask real fuel system problems. Reliable data starts with accurate instrumentation, and Motorplex by FleetEasy can ensure everything is working as it should.
Partner with Motorplex for Fleet Repairs in Auburn
At Motorplex, we focus on diagnosing the root cause before recommending repairs on anything else that might be impacted. That approach saves fleets time, money, and frustration, especially when dealing with complex systems like instrument clusters. We have fully equipped shops that offer fleet repairs in Auburn and Spokane, WA. We are ready to serve you and ensure your fleet vehicles run smoothly and safely, while giving drivers the accurate information they need to stay productive on the road.