Having trouble with the fuel gauge on your 2003-2006 Chevy Silverado or GMC Sierra? You’re not alone.  In recent years, we’ve read dozens of reports from Silverado and Sierra owners whose fuel gauges have just up and quit.  The result, of course, has been a lot of unnecessary stress and more than a few drivers getting stranded alongside the road because they didn’t realize they were running out of fuel.  Why is this happening?  Here are the two most common causes.

Now, the Silverado and the Sierra are, for practical purposes, basically the same truck, which is why we’re discussing them together here.

Silverado (and Sierra) Fuel Level Sensor

If you were to send a tiny camera deep inside your fuel tank, you would find your fuel pump and fuel sending unit, swimming in fuel and quietly doing the jobs their names would suggest.  Embedded among this happy apparatus, you would also find a fuel level sensor, which, also, would be doing the job its name suggests. Unless, as is all-too-common, it wasn’t.  In that case, and likely in your case, if you’re reading this article, the fuel level sensor has just gone out.  It has stopped sensing the fuel level or stopped letting the fuel gauge in your instrument cluster know what it’s sensing, leaving you to try to guesstimate how much fuel you have.  When this happens you’re left guessing how many miles you have left on your tank of fuel while your fuel level gauge bounces around from empty to ½ a tank  to ¼ of a tank to full and back again.  If this is the trouble you’re having, you’ll need to get your truck to a local mechanic for diagnosis and repair.

Silverado and Sierra Fuel Gauge Problems

The second and what seems to be the more common cause of Silverado fuel gauge or Sierra fuel gauge trouble is a faulty instrument cluster.  In fact, this is,unfortunately, a  common problem among most GM vehicles built from 2003-2006 – various gauges in the instrument clusters of these cars and trucks tend to fail as the mileage starts to get into the “high” zone.  This problem is caused by defective drive motors that were used on the circuit boards of these instrument clusters.  The defective motors have been linked to more than 30 different GM models and, though they have sometimes been covered by warranty or recall agreements, this is generally only the case for vehicles with less than 70 or 80 thousand miles on them.  This is often before they hit the “high mileage” zone where they tend to start experiencing problems.

How Do I Tell Which Problem I Have?

If your fuel gauge has stopped working and another gauge in your instrument cluster has stopped working, then you would probably be best off just having your instrument cluster rebuilt.  This is the less expensive of the repairs and something you are likely to have to do eventually anyway.  If only your fuel level gauge has stopped moving or is giving erratic readings, then it will be best to have the problem diagnosed by a local mechanic to determine if the fuel sending unit is the issue.

Who Can I Contact For Instrument Cluster Repair?

Contact Fred at Dr.Speedometer or call toll free 1-800-405-1056.

 

Has the fuel gauge in your 2003-2006 Chevy Trailblazer stopped giving you accurate readings?  Does it tell you you’ve got half a tank one minute, a quarter tank the next, then a full tank half an hour later?

Well, you’re not the only one.  Over the past few years, more and more owners of Trailblazers and other GM cars and trucks have had  trouble with faulty fuel gauges as well as other instruments.

Most often the failure of a fuel gauge in your Trailblazer will be caused by one of two things:

Fuel level sensor

If you were to dissect your fuel tank, you would find inside a fuel pump and a fuel sending unit bathed in fuel and doing, well, pretty much what you would expect something called a pump or a sending unit to be doing.  But built in with these two indispensable bits of machinery is another little something called the fuel level sensor, and this is where the arrangement gets buggy.

Fuel level sensors, which sense how much fuel you have and send that information to the fuel gauge in your instrument cluster, are, most tragically, prone to failure.  When this happens, it is left to you to try to estimate (or more often guess) how much fuel you actually have left in your tank because the gauge is bouncing around like popcorn.

If your fuel gauge is behaving erratically but the rest of your instrument cluster seems to be functioning normally, it may be best to visit your local mechanic to get your fuel gauge problem diagnosed.

Fuel level gauge

The second and, perhaps fortunately, more common cause of Chevy Trailblazer fuel gauge failure is a fault in the instrument cluster.  This problem is a result of defective drive motors that were used on the circuit boards of instrument clusters in some 30 or so different GM models.  Though this was covered for a time under warranty and recall agreements, few vehicles still fall within the 7 year, 70,000 mile limit.

The fortunate part of this is that it is a fairly straightforward problem that is relatively inexpensive to fix, if you find the right service.

How Do I Tell Which Problem I Have?

If any gauges besides your fuel gauge have also failed, it’s pretty likely that your problem is an instrument cluster one.  In that case, you can simply remove the instrument panel (we can give you detailed instructions on this) and send it to us – we’ll pay the shipping both ways – and we can replace the motors with new ones that won’t break down.

If, however, you haven’t had any trouble with any of your other gauges, though you may benefit from a cluster rebuild, you may want to have a local mechanic diagnose the problem first.

Thinking of changing the tires out on your Silverado or Yukon for some over sized off-road tires or maybe switching to some 20’s or bigger on  your Trailblazer or Suburban?  Something to consider is how it will affect your speedometer reading, read this great article to understand what affect  your change in wheel/tire size will have on your instrument cluster.

Speedometer Accuracy

No speedometer can be 100 percent accurate. In fact, most manufacturers build speedometers so they fall within a fairly narrow tolerance range, no more than 1 percent to 5 percent too slow or too fast. As long as a car is maintained at factory specs, its speedometer should continue to register vehicle speed within this range. But, if a car is modified, its speedometer may need to be recalibrated.

Changing tire size is one of the most common things car owners do that can affect speedometer accuracy. That’s because larger tires cover more ground in one complete revolution. Consider the example below.

Your car comes with factory-installed tires that are 21.8 inches in diameter. That means the circumference of each tire is 68.5 inches. Now let’s say you want to replace the stock tires with new tires that are 24.6 inches in diameter. Each new tire has a circumference of 77.3 inches, which means it travels almost 10 inches farther with each complete revolution. This has a tremendous affect on your speedometer, which will now indicate a speed that is too slow by almost 13 percent. When your speedometer reads 60 miles per hour, your car will actually be traveling 67.7 miles per hour!

Speedometer Calibration

All speedometers must be calibrated to make sure the torque created by the magnetic field accurately reflects the speed of the car. This calibration must take into account several factors, including the ratios of the gears in the drive cable, the final drive ratio in the differential and the diameter of the tires. All of these factors affect the overall speed of the vehicle. Take tire size, for example. When an axle makes one complete turn, the tire it’s connected to makes one complete revolution. But a tire with a larger diameter will travel farther than a wheel with a smaller diameter. That’s because the distance a tire covers in one revolution is equal to its circumference. So a tire with a diameter of 20 inches will cover about 62.8 inches of ground in one revolution. A tire with a diameter of 30 inches will cover more ground — about 94.2 inches.

Calibration adjusts for these variances and is done by the manufacturer, which sets up the speedometer gear to correspond with the factory-installed ring and pinion ratio and tire size. A car owner may have to recalibrate his speedometer if he makes changes that make his vehicle fall out of factory specifications (see the sidebar below). Recalibrating a speedometer can be done by manipulating the hairspring, the permanent magnet or both. Generally, the strength of the magnetic field is the easiest variable to change. This requires a powerful electromagnet, which can be used to adjust the strength of the permanent magnet in the speedometer until the needle matches the input from the rotating drive cable.

Harris, William.  “How Speedometers Work”  10 July 2007.  HowStuffWorks.com. <http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/speedometer.htm>   09 September 2010.

If you are in need of instrument cluster repair for any GM vehicle made between 2003 and 2006 contact Dr.Speedometer at http;//drspeedometer.com