04 GP GT ABS Activating at low speed

**jaycenk** · 01-27-2012

Hello again, I have an 04 Grand Prix GT II around 134,000 miles on it that I have been having an issue with the ABS system activating at real low speed. My wife drives the car so at first I almost didn't really think what she was describing was actually happening until it did it for me finally after 14 months of trying to understand what was happening. It's been going on for over a year. I changed the wheel hubs in the front due to bearing noise and play in them about 3 months ago and she said this problem of ABS activating did not go away. I read on line that it seems to be a common problem but could not get a real clear answer as to what is causing it. I figure since it was doing it before and after the front wheel hub change that those are fine. I am planning on changing the rear hubs real soon. Anyone have places I need to look for this problem. Tires are all the same size brakes are all in good working order. I get good bleed pressure from all 4 corners so I think the rubber lines are still ok. Any thoughts?

**BillBoost37** · 01-27-2012

A scan tool to monitor the wheels would be great. Say the hubs are not giving the proper or expected reading. or the wiring to them is gaining corrosion causing the incorrect reading. It's all a pain to diagnose.

**jaycenk** · 02-24-2012

Ok so got a mechanic friend to throw a snap on scanner on it and it said the code was communication link fail. he said it has something to do with the can bus. Makes sense if what he said is correct for this car. I also figured out that the ABS is not activating but going through like a start up cycle. He says it's loosing it's link or power and re cycling just like what it dose at start up. It only dose this at very low speed like below 5mph. The pedal stays nice and firm when it dose this cycle. Now he says it can be almost impossible to find since this could be a bad wire or bad module. So is it true for these cars that bus is basically run in a big circle and if any one module in the chain is loosing power or has a bad wire or is going bad in the loop it can cause everything after it to have to go back through it's test/start up procedure once the link, short or power are restored or corrected? Here are the wires and connections I have checked so far. I went through the fuse box and checked all fuses, puled them and added a tad of dielectric grease. I have not pulled any of the relays to test them but I am going to test them all tonight for function and resistance on the bench. The wheel speed sensors I have not had a chance to test or data log. but I inspected the front wires and harnesses they look fine. Still need to look at the rears. I pulled the harness at the ABS module and checked all the pins and added grease to them. There has been no change with the problem. I will say it has been doing this for years. It used to only do it every now and then like 1 to 2 times a month. Now it is doing it 2 to 3 times every time you drive it. Are there any problem areas that I should be looking for wires grounding out. Also where the hell is the PCM located in these cars?

**Fivefingerdeathpunch** · 02-24-2012

pcm is in the air box.

**jaycenk** · 02-24-2012

Found it Thank you for the assist Five finger.

**jaycenk** · 02-26-2012

Is there a good scanner that can scan abs and live stream the wheel sensor data on the market to help me figure this out? I hate to have to pay the local dealer 100+ to hook up a tech 2 if I can just buy a hand held for a little more. I don't have the need for a $3k snap on unit that the mechanic I took it to used but it was nice. Anything worth a crap?

**jaycenk** · 03-02-2012

Update,
So I cut open about a foot of the sensor harness on the left front and took the tape off the wire junction where the left front abs wheel sensor harness meets with a main harness just inside the left front frame rail under the top radiator hose. I did nothing else to the harness inside the frame rail except remove the tape. I did unwind the twisted pair about a foot up from where it plugs into the abs wheels sensor on the left front to inspect for any visual problems. I saw nothing alarming and let it twist back together on its' own looser then it was stock and taped it back up with electrical tape, re secured the harness to the factory clips and plugged it back into the wheel sensor. It has not done any of the low speed activating since. Go figure right. I am going to monitor this for a while and report back again. It has been fine all week with just normal test activating at the normal times as it always has. Usually after backing up and going to drive.
I was planning on data loging it to see what was going on but untill it will do it regularly again I can't do that so we shall see how long this lasts.