OBD scanner

Diagnostic fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. We have to know the exact fault code number to figure out where to start. When a part is referenced in a fault code, it is actually the cause of that code about half of the time. First we have to rule out wiring and connector terminal problems.

For a wheel speed sensor, there are multiple ways it can fail. This type of sensor is a coil of very long, fine wire wrapped around a magnet. A voltage pulse is "induced" in the coil of wire when it moves in relation to the magnetic field. That is how all generators work. In the case of a wheel speed sensor, the magnet creates the magnetic field, and a rotating toothed wheel disturbs, or bends the magnetic field when a tooth moves past it. That bending is the movement that induces the voltage into the coil of wire.

You did one test on that sensor. The resistance reading tells you there is no break in the coil, and if you measured it from the terminals on the computer's connector, you included all the wires and connector terminals in that circuit too. It is important to understand when resistance values are listed in a service manual, those are only for reference. If you take a hundred properly-working sensors, a good percentage of them will measure outside that acceptable range. When we check them, we're basically looking for 0 ohms, the wires are shorted together, (typically pinched or laying on hot exhaust parts), or an open circuit, (infinite reading), indicating a cut wire. We also have to check if either wire reads 0 ohms or real low resistance to ground.

If any of those electrical tests fail, it will be detected during the system's six-second self-test when the ignition switch is turned on. The appropriate fault code will be set, and the yellow warning light will stay on.

That all pertains to the electrical tests. You also have to consider the mechanical part of it. Just because the coil of wire is intact and has continuity, you need the tone wheel, (toothed wheel), to be close enough to disturb the magnetic field. A fairly common problem used to be that tone ring would crack. The sensor detected that extra gap and generated a pulse for it. When driving straight and not applying the brakes, the computer expects to see the same frequency, (number of pulses per second), to show that both wheels on that axle are rotating at the same speed. This is where it is critical to have tires with the same outer circumference. At first the computer will assume you are going around a curve to make one wheel rotate faster than the other one, but eventually it will figure out the two speed sensors are indicating different speeds. An appropriate fault code will be set, but the difference here is it could take as much as a mile for that discrepancy to be detected. The yellow warning light will be off until that problem is detected.

Because movement is one of the three ingredients in generating a signal, (coil of wire, magnetic field, and movement between them), the speed of that movement is also a factor. That is why generators are very inefficient at low engine speeds. GM has had a real lot of trouble with their front-wheel-drive front wheel bearings with built-in wheel speed sensors. Those sensors develop real wimpy signals to start with, then, when the wheel bearing develops a little play, which is normal for any wheel bearing, the tone ring can move away from the sensor just a tiny fraction of an inch. That extra gap, coupled with the lower efficiency at lower speeds, makes the signal drop out to the point the computer cannot read it. The common symptom is "false activation" at low speeds. You will feel and hear the buzzing of the system activating when the brakes are applied, below about ten to twenty mph and no wheel is locking up. As the play in the bearing increases, it can cause a total loss of speed signal. Resistance readings will be normal. It is a mechanical problem causing this. The yellow warning light will turn off after the six-second self-test, and it will stay off until the car starts to move. That is when the computer expects to see signals from all four speed sensors at the same time. The fix for this is to replace the entire wheel bearing assembly with its built-in speed sensor. These repeat failures can occur in as little as 15,000 miles. The dealers' scrap metal bins are full of these, but as a point of interest, this is the same bearing that is used on cars without anti-lock brakes. A bearing that has to be removed for a speed sensor issue can be used on any other GM front-wheel-drive car, and will likely last the life of that car. The sensor coil can be pried off and discarded or in most applications it can be left on and just not be plugged in. As a further point of interest, it is common to find this replacement bearing costs less with the speed sensor than it does without it. If you do not have ABS, buy whichever one is less expensive.

Another common GM problem has to do with their trucks. They use a more common and more reliable type of speed sensor. These have a problem with rust forming under its mounting ear that pushes it up away from the tone ring. The increased gap causes a reduction in the signal voltage. Typically the signal is strong enough to be detected at higher speeds, but at low speeds the false activation is the common complaint.

I shared that wondrous story to give you some idea of the things to look for on your car. One other thing to look at is metal filings built up on the tip of the sensor. Since it is a magnet, chips of rusted metal will cling to it too. Any metal in the gap will deflect or reduce the changing magnetic field, possibly to the point almost no signal voltage will be developed. The electrical integrity of the circuit and sensor is still okay, but with no signal, the computer cannot do its job, so it shuts the system down after setting a fault code and turning on the yellow warning light.

Be aware too a lot of people create a problem when they replace a brake rotor or drum, and get one without the built-in tone ring. On the front of front-wheel-drive vehicles, those are usually on the outer CV joint, except for GM cars, but on trucks it is just as common to find them pressed onto the back of the rotor.

As for your scanner question, typically anything that can access an anti-lock brake Computer is going to be expensive. I have a Chrysler DRB3 for my vehicles. A lot of independent shops bought them because with an extra plug-in card, it will do emissions-related stuff on any brand of vehicle sold in the U.S. Starting with 1996 models. The problem is it will not do ABS stuff on other brands, and it became obsolete on a couple of 2004 models, and on all models by 2008.

Also be aware there is a big difference between a scanner and a simple code reader. The scanner is equivalent to all the equipment in a hospital. The code reader would be the doctor's stethoscope. Since almost forever, code readers could only read codes in engine computers. Those were what they used at auto parts stores where they will read codes for you for free. In the last few years, there are some code readers that can read codes in other computers. The problem with these is they tell you which circuit needs to be diagnosed, but that is all. A scanner will display sensor information, show which switches are on or off, and most importantly, they're "bidirectional", meaning you can talk back and tell a computer to do something. As a practical example, to take voltage readings in a dead radiator fan circuit, you would need to run the engine long enough to get it hot enough so the fan should be turning on, but how do you know when you have reached that temperature? With a scanner, you simply command the computer to cycle the fan relay on and off while you take measurements in the circuit.

One word of warning if you look on eBay. If you find a new "scanner" for less than a hundred bucks, it is not going to access every computer on every car. There can be up to 47 computers on a late 1990's Cadillac. Also, the update rate is extremely slow. You will get your sensor information, but instead of seeing ten readings that update multiple times per second, you might only see four or five readings that update as little as once every five seconds. If you are analyzing a throttle position sensor, you would have to hold it open, then wait to see if the reading finally jumps to what you expect it to be. You will get the information, but it is agonizingly-slow once you are used to using a professional tool.

Given the age of your car, you might consider visiting some local independent shops to see if they have a scanner they are considering selling. Also, they are visited once a week by the guys who drive the tool trucks. Those are good places to find new and used scanners. Ask to "see what's in the 'used' drawer". A shop may not be happy with what the tool truck guy is going to give them for trade-in, so they might wait to buy the new scanner. If they can sell it outright for more money, they might appreciate the chance to do that. A real popular scanner used to be the Snapon MT2500. It was called the "red brick" because of its shape. You need to plug in two cartridges, and you updated it by buying a newer cartridge. Those are all over eBay and are pretty cheap. I have a Monitor 4000 for my older cars. It was built by the same company that built Chrysler's older DRB2. They look very similar, and both use a plug-in cartridge, but they are not the same. The latest Chrysler cartridges cover all the models through the 1995 model year. The monitor cartridges cover GM and Ford, as well as Chrysler models, at least through the 1995 model year. I never looked for newer cartridges than that since I use the DRB3.

Also consider there is a dealer version for your car like the DRB3 is for mine. GM's scanner was the Tech2, and I think that was used for Toyota's too. It does the same things on GM products that the DRB3 does on Chrysler's. Both were issued to the dealers, and were often in constant use by someone.

For aftermarket scanners, some of the popular names are Matco, MAC, Genysis, and Snapon. A few years ago a lot of mechanics preferred the Genysis. I did not use them enough to know much about them, other than they worked fine. Today probably one of the most popular is the Snapon Solus Edge. My friend has one, but a word of warning. Snapon is extremely proud of their equipment and they charge accordingly. I will never buy one because it has to be updated every year by the tool truck driver, and I have heard those software updates cost anywhere from $900.00 to $1,500.00. Worse, you cannot skip any years. If you find one of these on eBay, it will be dirt cheap if it has only been updated to say, 2008 or 2010. A new scanner costs around $3,900.00, which is not bad, but just like with expensive ink for cheap printers, you'll go broke buying the updates, if you need them. Those updates would not be of much value for a 2001 model, but in later updates there could be some corrections to the software that applies to your car. I looked at getting one of these for my 2014 truck, but if I bought one updated to 2010, it could cost $4,000.00 to update to cover my four-year-newer truck. Might as well buy a new one. Instead, I will use my friend's and let him pay the outrageous cost of the updates. This scanner would probably be my recommendation for you as long as you are aware it will have a low value when it comes time to sell it. Last time I looked on eBay, there were a few for around $700.00.

For my final comment of value, be aware the computer language used for computers to talk back and forth to each other has gone through changes over the years. Between 1983 and 1995, every manufacturer had their own software and their own computer language. A scanner had to have the ability to communicate with each brand it was meant to be used on, but the capabilities were quite limited compared to what scanners can do today. Starting with 1996 models, the language was standardized and the diagnostic connectors were all mounted under or near the steering column. This is referred to as the "on-board diagnostics, version 2", (OBD2) emissions system. Along with being much more sophisticated, it includes oxygen sensors after the catalytic converters. Instead of a few dozen fault codes, this system can detect up to around 2,000 defects, each with its own fault code. There can be a couple of dozen codes that all refer to oxygen sensors, but mean very different and more specific things. This system would include your car.

The OBD2 system was replaced by an even more sophisticated "CAN BUSS" system that turns every switch and other electrical item into a small computer module. The claim is it makes diagnosis easier, but in fact, all this unnecessary electronics causes more problems than before. The moisture, dust, and vibration in a car is the worst possible environment for electronics to live in. This is why there are so many electrical problems people are looking for help with today. If you find a scanner that does not work on CAN BUSS vehicles, it will have lower value to buy it and when it comes time to sell it. But you also want to be sure if you find one that does CAN BUSS cars, it has to also have the capability to do your OBD2 car. The CAN BUSS system first showed up around 2003 or 2004, but not on all models. Some models did not switch to it until around 2008.

If you find a scanner you like on one of the tool trucks, ask if you can plug it into your car to be sure it works. Most of them are powered through the diagnostic connector. The ignition switch has to be on, then you do not want to see a message on the screen referring to an inability to communicate. That can be caused by a blown fuse on the car, but I would not expect to find that since some other scanner worked on it recently.