Surge when in closed loop - diagnosis problems [Archive] - Forum


View Full Version : Surge when in closed loop - diagnosis problems

04-16-2008, 05:52 PM
Overview- My 99GAGT has a 200-300RPM surge when going down the highway. It kicks the cruise off almost everytime it does it-if the cruise is engaged. So I started the diagnosis.

Diagnosis- I've used a snap on brick scan tool as well as a GM tech 2 and have discovered that the surge is the torque converter going out of lockup and then engaging again. The torque converter has a brake switch that it goes through that the scan tool shows is working properly. The cruise is also run off of this brake switch.

Problem?- I believe since the PCM has been updated that it is the torque converter clutch solenoid-i can't think of any other thing that it might be? Anyways, the problem is I dont know how to test the solenoid! I cannot find any wiring diagrams that point to what pins on the connector to backprobe to ohm it. I know they are red and tan. Is there any other way to test it? HELP PLEASE THIS HAS BEEN DOING IT FOR 6 MONTHS AND I WANT TO DRIVE MY CAR!!!!!!!!!!!!!

04-16-2008, 05:55 PM
this shouldnt stop you from driving your car unless its constant....

04-16-2008, 06:23 PM
it's VERY constant, were talking every 5-10 seconds not to mention fuel economy is in the gutter because of it. I've been driving my truck everywhere but i need to get the car going now that it's nice.

I should add that there was no codes set.

04-16-2008, 07:53 PM
Did you run a live plot on that TCC brake switch to see if the voltage dropped off? Sometimes the changes are so quick its hard to notice staring at a data list.

If you don't know how to get to a live plot with a Tech 2, hit the "Select Items" soft key, highlight the TCC brake switch and press enter so an asterisk is besides it. Then hit "Done". If you zoom in on the graph you'll notice the resolution is higher. You can also take a quick snapshot with a beginning trigger if you need to.

One other thing to consider is if you're driving up alot of hills or even overpasses, sometimes the TCC will kick off like this.

04-16-2008, 08:28 PM
Also check your plugs and wires - you might be getting a slight misfire.

04-17-2008, 11:26 AM
it's not plugs or wires for sure, we've put new plugs and wires w/in the last 1000 miles and watched misfires on the scantool. I'm going to backprobe the brake switch and watch it on a test drive and see what that's doing.

04-17-2008, 06:49 PM
Other than figuring out if its the brake switch, you might want to call SPS and see if you can get a VCI number to reverse the programming. I'm not sure why you updated the PCM but that issue might return as a result.

Just depends on which is more annoying I guess.

04-17-2008, 09:01 PM
i have a '01 gagt and have also had surges. im not to engine savay so i took it to the local car shop and a dealer. they told me that the codes were tellin' that it was the EGR valve and that it could be stickin'. that got tested and said that wasnt it and it might be in the computer and to get it flashed or rebooted. unfortunatly it was neither. but it could be a consideration for yours. i have been drivin' it for the past month since the auto shops and the past 8 since it started. however, i have never experienced it with the cruise on because i dont use it more that once every two months. well i hope i might have given u a little help. i know u gave me another reasoning for it and to try the solenoid. - bratthauer

04-17-2008, 09:21 PM
Yea that's the hard part is there is no codes and the computer has already been flashed. Everything is pointing towards the torque converter but what exactly it is I cannot pin-point it now.

10-15-2008, 10:35 AM
Yea that's the hard part is there is no codes and the computer has already been flashed. Everything is pointing towards the torque converter but what exactly it is I cannot pin-point it now.

hey i dont no if u got your GA fixed yet but mine ended up being just a dirty mass air flow sensor. that may not be the case with your tho.