02' Century Codes

Hi, I have a simple but yet complicated question! When I bought my buick from the dealer, some warning lights would come on frequently, but I had their repair shop fix it, to which they told me ended up being a MAP Sensor. Then one day about a month later the "Service Engine Soon", "Anti-Lock", and "Trac Off" lights came on. I took it back and was told of the problem. I don't recall what the code was, but they said it was the ABS Sensor. At the time my car was under waranty, however, this was not covered. My warranty was about to run out in about a month or so, so I decided to wait and just have it fixed by my boyfriend. I went and bought the front wheel-bearings for the side I was told needed the sensor. He took it to his friend's garage (who does mechanical work), and they put the whole unit in. Well, my question/problem is: How the heck do I reset the computer to get these codes out of there for the lights to go out?? We tried disconnecting the battery for several hours, and it didn't work. Do I have to take it to a dealer?? :uhoh: Please Help Me!! Thank You!!

The SES light and DTC error codes can be reset with an odb-ii scanner. Hopefully the bad wheel sensor was diagnosed correctly and it is not one of the 3 others. ABS codes should clear out after a few drive cycles if the part replaced did, in fact, correct the problem.

Disconnecting the battery may clear certain codes but not all and it will not clear a SES light.

I have a field expedient method that works to clear the SES light and you do not need a scanner to do it. Let me know if you would like to try it.

The wheel bearing unit was replaced at least a couple months ago, so it has been driven almost daily to work and none of the lights went out. So I guess it is possible that it was not the right one then? Can you interchange the part or do I have to keep buying the whole unit until I find the right one that went bad?
Yes, I would really appreciate any options of your knowledge to clear these codes rather than use a scanner because we do not have one, and I don't have the $ to take it to the garage! Thank You!! :smile:

The wheel bearing unit was replaced at least a couple months ago, so it has been driven almost daily to work and none of the lights went out. So I guess it is possible that it was not the right one then? Can you interchange the part or do I have to keep buying the whole unit until I find the right one that went bad?
Yes, I would really appreciate any options of your knowledge to clear these codes rather than use a scanner because we do not have one, and I don't have the $ to take it to the garage! Thank You!! :smile:

A good ABS capable scanner or one that can retrieve GM CHASSIS codes is normally required to determine specific wheel sensor/hub. The hubs are not interchangeable and it maybe hit and miss until right hub is found if proper diagnostics equipment is not available.


Here's a field expedient method to reset PCM:

Note: If radio Theftlock is activated make sure you have your codes because removal of battery cable may activate a "LOC" indication on the radio.

Remove only the battery positive cable.

Insert key in ignition and take key to full engine start position and hold there for minimum of 1 minute. (Of course, engine will not start and no instrument lights, etc.).

Take key back to off, however, it will not remove at this time and will be stuck. No problem.

Next re-connect battery positive cable. You will hear relays chatter.

Now turn key forward and back. It will now remove.

Finally, start engine. SES light should be off and all DTC error codes cleared.

Good luck!

Ok, we tried this option today with disconnecting the positive battery cable and turning on the key and it did not work :shakehead Are there any other ways that can be considered? When I took it to the garage for the codes, it came up that it was the frt pass side ABS sensor... so they told me :dunno: and this is what we changed. My boyfriend wanted to know though, how would this work anyway when there is no power source to anything? Thanks again!

Ok, we tried this option today with disconnecting the positive battery cable and turning on the key and it did not work :shakehead Are there any other ways that can be considered? When I took it to the garage for the codes, it came up that it was the frt pass side ABS sensor... so they told me :dunno: and this is what we changed. My boyfriend wanted to know though, how would this work anyway when there is no power source to anything? Thanks again!

It looks like you will need an ABS capable scanner with reset capability because they are Chassis ABS codes. The object to removing power is to get the control modules to reset possibly clearing any fault information stored but it looks like it will not work for the ABS system. The ABS system generates fault codes via an electronic brake and traction control module.

Alrighty then, thank you very much for your time! We understand about disconnecting power to reset electronic components, what he didn't get was the point of turning on the key when there was no power. No big deal anyway since it didn't work. Guess I will have to take it to the garage unfortunately :frown: but thank you again for your help!!

SES lights will clear out after 40 drive cycles if the problem is corrected. ABS codes and air bag codes work differently. When you have an ABS code if the correct part is replaced the ABS light will go off. When you cycle your key on the ABS self-tests and if no problem is found the light will go out. If you have a problem the light will stay on. Air bag codes work the same way so does HVAC and BCM codes.

Since you still have an ABS light on chances are that you still have a problem. I could bet that you have a broken wire to the speed sensor and I would bet I could find it without much effort. Open your hood, look below your air cleaner box you will see a silver cannister for your AC system. Now look close you will see a wiring harnass running right next to the cannister. If the wiring is hitting the cannister you more than likely will find a broken or almost broken wire in the spot.

Now the way the ABS self tests the system is the computer sends 5 volts down the wire and looks to see the voltage drop coming back. If the computer gets back 5 volts the system will see a working sensor. But if you have a break or partial break the computer will see less than 5 volts and turn on the ABS light. Scanners are useless in finding partially or totally broken wires. The ABS computer is faster than the scanner and the scanner will not see a fault fast enough to even register the problem. Only thing you will get is a fault code. I find using a multi meter is the way to find ABS problems.

BTW the PCM stores 4 differnt levels of codes:
Type "A" DTC turns on the SES on the first fault and stores the fault parameter.
Type "B" DTC turns on the SES on the second fault and stores the fault parameters.
Type "C" and "D" stores the fault parameter without turning the SES light on.

Since you still have an ABS light on chances are that you still have a problem. I could bet that you have a broken wire to the speed sensor and I would bet I could find it without much effort. Open your hood, look below your air cleaner box you will see a silver cannister for your AC system. Now look close you will see a wiring harnass running right next to the cannister. If the wiring is hitting the cannister you more than likely will find a broken or almost broken wire in the spot.

Now the way the ABS self tests the system is the computer sends 5 volts down the wire and looks to see the voltage drop coming back. If the computer gets back 5 volts the system will see a working sensor. But if you have a break or partial break the computer will see less than 5 volts and turn on the ABS light. Scanners are useless in finding partially or totally broken wires. The ABS computer is faster than the scanner and the scanner will not see a fault fast enough to even register the problem. Only thing you will get is a fault code. I find using a multi meter is the way to find ABS problems.



Good point Flatrater. A multimeter does come in handy providing the person with the problem has access to one, knows how to use it and is knowledgeable with the circuit. The problems I've had with hub/wheel sensors is some wiring but mainly with aftermarket hub/wheel bearings assemblies like from Autozone. They are either flaky and you wind up with bearing noise or the wheel sensor does not meet specs electrically. I found the GM OEM hubs to be of better quality. In addition to checking input wiring I make it a habit to run a resistance check of the wheel sensor before installing the new hub by ohming it out with a multimeter and see if it's in a specified range of resistance per the service manual. Undo the electrical connector at the hub and go across the 2 pins on the sensor/hub side. Also, it is a good idea to check the wiring and electrical connector to the hub which runs along the control arm to the hub assembly.

I believe these are the resistance specs at 68 degrees F:

Rear wheel sensor (1030 - 1180 ohms)

Front wheel sensor (1020 - 1137 ohms)

Resistance is a good test but may I also suggest that you jack up the suspect wheel. take your meter setting the leads across the sensor and just spin the wheel by hand while you watch the meter on AC volts. Spinning the wheel should produce an AC voltage. The faster you spin the more voltage you make which will tell you that the sensor is working.

Personally I tend to stay away from using a resistance check to find a problem since I have been burned by that test many times. Resistance is a good test as long as you know that the results are limited in what it can find. I like to use a voltage drop check which finds more faults. Don't get me wrong resistance has it's place and I still use it but I prefer different tests.

Whenever I get a new tech in the shop and I see them using an ohm meter to find a fault I pull out my bag of tricks. I get a wire strip the insulation back and cut every strand of copper except one or 2. Next I ask the tech to check the wire and tell me if the wire is good or bad. Every time I get the wire is good till I tell them to tug on the wire. when the wire breaks I say it couldn't be so good.

If you want a nice piece of test equipment that doesn't cost alot get ahold of a sealed beam headlight. Run 2 wires to the headlight and you can plug it into any circuit. If the bulb is dim you know you have a wiring issue. Bulb bright means the circuit is good and the device is bad. It also makes a great short finder. Installing the headlight into the fuse of a shorted circuit the bulb will stay out. Start moving the wiring and when the bulb lights you found your short. I have a headlight in my toolbox and it gets used often. Because you don't have to be near the bulb like a meter you can go all around the car while you look for the problem. The light beam is easy to see. And if the light lights you know you have voltage, amps and your resistance is ok for under 5 dollars in test equipment.

Thank you both so much! I will have him check out these other options as well, before taking it to the garage just yet! Depending on the weather, it'll be this weekend sometime and I will let you know what happens!!

Hello again! I wanted to let you know that my boyfriend finally got the chance to check out the resistance specfications for the sensors,and they all passed with excellent results!
The better part to this is ... he went over the wiring as you mentioned,and he did in fact find the problem there! The wires that run along the control arm ... they came across the A frame and were badly chewed from a metal plate that is welded there. I guess he said the corners of the plate caught the wires and left nothing to them,so he spliced them back together and presto!! Problem fixed!! Thank you so very much!! I highly appreciate your help because you have saved me $hundreds$ THANKS!!