2003 GMC Yukon Dash Cluster

Tiny
LAZARO173
  • MEMBER
  • 2003 GMC YUKON
  • 4.8L
  • V8
  • RWD
  • AUTOMATIC
  • 140,000 MILES
The ABS, Brake Light, Traction Control light have all come on. I had it serviced and was told that the abs wheel speed sensor at the front hubs had to be replaced and were then replaced. Nothing has changed. Before I keep paying for things that don't correct the problem, can you give me some advice? Also, now the temp, fuel and the alternator charging gauges have stopped working, any ideas?
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Monday, March 23rd, 2015 AT 5:53 PM

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Tiny
CARADIODOC
  • EXPERT
For the gauges, start by checking for a blown fuse, both inside and under the hood.

For the ABS problem, how long did you wait between the warning lights turning on and the problem was diagnosed? GM has two real common ABS sensor problems. One affects front-wheel-drive cars and some newer trucks. A different problem affects your truck. The front wheel speed sensors develop rather wimpy signals to start with, then, over time, rust builds up under the sensors and pushes them away from the toothed wheels. That makes the signals get even weaker until the computer can no longer read them. A missing signal will be detected, a diagnostic fault code will be set, the warning lights will be turned on, and the systems will be turned off.

The fix for this is to remove the sensors and clean off the rust, then they can be reinstalled. To verify this you have to know the exact fault code number and description because to the computer there's a big difference between a missing signal due to that rust vs. A missing signal due to an electrical problem.

Where the problem comes in is the computer is constantly comparing a number of signals and operating conditions to each other. In this sad story, it expects to see all four wheels rotating at the same speed when you're not applying the brakes. When one signal goes missing from one wheel, the computer knows it can't rely on that wheel speed to compare to the others, so it suspends those tests. No other fault codes will be set related to wheel speed sensor signals. When you have this problem diagnosed right away, there is typically just the one thing that needs to be fixed.

Since that rust that causes a signal dropout affects both front sensors the same, it can be expected the same thing is going to happen to both of them at roughly the same time, typically within a few weeks or months. If you wait to have the first problem diagnosed, as many people do, there is plenty of time for a second problem to show up, but since the self-tests have been suspended, that second problem isn't detected, and there's no diagnostic fault code set for it. All the mechanic has to go on is the one fault code, and that's what he bases his estimate on.

Once that first problem is repaired, when the mechanic goes out on a test drive is when the self-tests resume, and that's when the second problem is finally detected, a new fault code is set, and the warning lights turn right back on again. He has to start the diagnosis all over again, and that's when he first learns of the new problem. This is real frustrating for mechanics because they hate having to tell you more parts are needed, and it's frustrating for car owners because they incorrectly assume the mechanic is incompetent, didn't diagnose the problem correctly, and charged them for parts and repairs that weren't needed. Better communication would help but even a lot of mechanics don't understand how this can happen.

The other thing you must be aware of is diagnostic fault codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When your mechanic diagnosed the sensor needed to be replaced, that would be due to the fault code indicating an electrical problem with that speed sensor's circuit, typically a broken wire. That problem will be detected as soon as you turn on the ignition switch, and the warning light will turn on right after it goes off after the six-second self test.

A signal that's missing because of a mechanical problem, like that rust under a sensor, will not be detected until the truck has been moving enough for the other three sensors to generate signals. You'll see that as the yellow ABS light goes off after the six-second self test, then it will stay off until you start driving. With this problem there is no electrical defect. The fault code will relate to a loss of signal, but not why.

At this point you need to find out which fault code is set. If it refers to the same wheel as before, the diagnosis likely was incorrect. If it refers to a different wheel or different problem, that may just be due to coincidence that two things happened at the same time.
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Monday, March 23rd, 2015 AT 6:53 PM

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