Thought I would pass this info along...I have been chasing an ABS light on the 98 GT sedan with no luck. I bought a scan tool that says it reads ABS codes, and while it will pull codes on the 02 GTP coupe, it will not on the 98. BUT I found the info that you need to effectively diagnose ABS issues without a scan tool.
First stop is the hub bearings. Using a multimeter set to resistance, you should get a reading of between 850-1100 ohms at the pins of the hub bearing connector. No reading means the sensor is bad and the hub needs to be changed. All the hubs on my 98 checked out so the issue was either in the wiring or the EBCM (Electronic Brake Control Module) itself was bad. What I finally found was a wiring diagram for the connector that goes to the EBCM. Checking resistance there checks BOTH the hub bearings and the wiring that goes to the EBCM.
Slide the keeper out and unplug the large harness from the EBCM. When it comes off, the pins are on the EBCM side and the sockets are on the connector. Looking at the connector, you will see 3 rows of sockets and very small numbers embossed in the corners. Pin position #1 is at the upper right and the first row is numbered right to left 1-11. The 2nd row is numbered 12-19, and the 3rd row 20-30.
Using your multimeter, check for the same 850-1100 ohm resistance between the following pin locations:
#2 & #3 pins Right rear wheel
#4 & #5 Right front wheel
#20 & #21 Left Front wheel
#22 & #23 Left rear wheel.
On my 98 I got good readings at all except the LF wheel, which didn't read at all. Since I got a reading at the hub itself, that means there is a wiring issue somewhere in between the hub bearing and the EBCM. The wiring for the sensor bundles in a loom that routes around under the transmission, so rather than check the existing wiring, my plan is to simply run new wiring from the EBCM connector to the LF hub bearing connector. I'll be working this weekend on it and will report back.
If you get good readings for all 4 hub sensors at the connector, then it's likely the EBCM is bad. Go to Cheap ABS and they will rebuild your unit for $99 plus shipping. You only need to remove the electronics, not the hydraulics, so you can drive the car while you mail the unit away for repair.
Here is the ABS wiring diagram, AFAIK it's good for 98-03.
I have been looking for this wiring diagram and pin-out map for a loooong time, it's a huge help is tracking down these ABS issues, so thought I would pass it along.
