Impala Forums banner

1 - 2 of 2 Posts
R

·
Guest
Joined
·
0 Posts
Discussion Starter #1
I have an 89 gmc pick up that has sometimes gives me a speed sensor fault code(service engine) or a ABS fault code(brake light flashes) or sometimes the speedometer will not read anything(no codes). I tried replacing the speed sensor on the tail shaft of the transmission but no change. I also heard about a module (DRAC ?) that splits the speed sensor signal to the ABS and the computer but couldn't find in in the dash.
Anyone have a similar problem?
 
M

·
Guest
Joined
·
0 Posts
Discussion Starter #2
I own a shop, and have done extensive work on these systems. Depending on which system you have, the speed sensor is sometimes in the transfer case on 4x4 vehicles. The one you changed may just read the output shaft speed, and not the vehicle speed. When you changed the sensor, did you check the reluctor inside the tailhousing to see if it had came loose? Sometimes they will come off, and spin one day, and not the next. Use a screwdriver to see if you can hold it while spining the driveshaft by hand, if so then the clip has came out of it. Check each wheel that has a sensor, and make sure they are clean, and working properly. Sometimes brake dust (which is metal) can build up on the sensor so bad that it will read eratically. Look at the top of the rear end housing, to see if there is a sensor up there too. The reason you can't find the component that splits the signal to the ABS, it's done on the speedometer circuit board probably. Go to the library and pull a Chilton's Repair Manual to take a good look at the wiring diagram for this circuit. I really don't think these codes are related. Check the connector plugs that goes to the speed sensor for plugs that are spread apart, and not making good connection. Purchase a can of electronic cleaner from the parts store, and clean all connections that you can. The wires that go from the speed sensor to the computer may be bad. If the speedometer stops, then this means you are loosing signal. If the code indicates the speed sensor, then one must inspect the complete wiring all the way back to the computer sometimes to find the problem.
These sensors are generators, and emit an (AC) electrical charge (signal) that can be read with a multi-meter on the mili-volt scale. This means you should be able to use a meter, and spin the wheel with the meter attached to the sensor, and get a voltage reading. The faster the shaft, or wheel spins the more electrical charge is created. If it doesn't read one way, reverse the leads from the meter, and it should work then. Since this electrical signal goes to the speedometer, and the others work the ABS, any loose, or shorting wire to ground can cause all kinds of freaky things to happen. If you have an automatic transmission, the signal from the speed sensor also helps the computer determine the shift points. You really need to know what the code was for the brakes. The speed sensor code, the speedometer not working sometimes, I don't think are related to the ABS. Mess with the emergency brake to see if the ABS light comes on. I have even found one that had a bad switch for the emergency brake make the light come on, but it had no codes set. I think the module (Drac) is probably on the board for the speedometer, and you may even have a bad, cracked board, or what is known as a (a loose connector on the board) cold solder joint that didn't take when the board was made. It will look different from the others, and may need touched up with the soldering iron and some acid core solder.
Glad to help out, Good Luck!!!
 
1 - 2 of 2 Posts
Top