Foiled Again

[TooManyHobbies]

Went down to Fayetteville this weekend to try to finally get this thing in the 9s. The good news: The traction issues I have been having seem to be solved. I love these new MT P305/45R17 Street R tires. The bad news: Computer/electrical gremlins and a very warm December.

Rick flashed a tune for the new tire diameter. He went to take it for some street tuning and the car would stop scanning. We messed with it for quite awhile, trying a different computer and interface. Same behavior. Went to reflash the tune and it would not write a new tune, would not read a tune. Crap. More debugging attempts and no dice.

The car seemed to run fine, so went to the track to make the best of things. The tires hooked really well and car ran and shifted pretty well. My best was a 10.19 on a 1.55 60'. DA was very high for December, about 1300. It was hooking well enough that he probably could have added some timing back on the launch. He also thought it was still a tad rich. No way to adjust anything though, or even scan to verify anything. Was setting a CEL for an ECU error though that I could reset.

Did multiple runs at the track and drive back to Rick's to swap street tires on and load it back up. No issues. Later that night went to drive to the hotel and $&#*@ it would not shift past 2nd. Gremlins mating and multiplying. Pulled into a gas station, shut the car off, and then restarted it. It would now shift up to 4 which made it possible to drive to the hotel. The next morning it was time to go home. Time to see what the gremlins did overnight. Was able to get into 6 and seemed to be behaving fairly well. Got down the road and on the interstate, and back to only 2nd gear, safety mode. Nursed it to the next exit and pulled over to reset it and go back to Rick's. Tim King was caravanning with me. He was driving his truck. He had left his car and trailer at Rick's. It drove back to Ricks initially shifting nearly normal. The speedometer was bouncing around like crazy though and the CEL/see dealer would sometimes be on sometimes off.

Anyway, towed it to Tim's house and then I was going to drive it the rest of the way to my house. Got it off the trailer and started for home. Initially behaved really well, then started seeing some bouncing speedometer, and CEL was intermittently set. Shifted nearly normal until I was almost home. Made it there and parked it.

Now I have some fun debugging to do. Current plan:

1. System reset - disconnect battery and touch positive and negative cables to completely drain the system. Then see if I can read a tune. If I can, write a tune.
2. Look in and under it for frayed or melted wires.
3. New ECU
4. New TCM

Anybody have any other suggestions to look at?

[Phil@PnP Tech]

Kinda sounds like it's a problem in the gmlan lines... I think it's supposed to be 60 ohm between high and low. I'd also check for a short to ground in either wire. Your triple gauges act normal?

Edit:
Here is the procedure to test it...
Scan_Tool_Does_Not_Communicate_with_High_Speed_GMLAN_Device.pdf

[TooManyHobbies]

Something is up with Communication Bus A, the current codes are P0606 ECM/PCM Processor, P0700 Transmission Control Module (MIL Request), and U0073 Control Module Communication Bus A Off. The one triple gauge that is on the CAN bus is the oil pressure gauge and it is pegged at zero. I did the system reboot by disconnecting the battery and grounding everything out and no change. I inspected wiring a little and did not see anything amiss. Tomorrow night I will pull down the dash panel to inspect where I tapped into the CAN bus for the gauge.

[gr8lover]

That sucks man!!! good luck with it... stuff like this is frustrating for sure.

[TooManyHobbies]

Seems to be fixed anyway.

Tonight I took down the drivers side kick panel to access where I connected the oil pressure CAN bus gauge into the factory wiring. This was tapped into the wiring at the steering yaw sensor. I figured that if the wiring would fail it would be my fault. Since I had already inspected other potential problem areas, this was the place to look next. I disconnected the yaw sensor connector and fired the car up and took it for a spin. Stability control error as expected, but shifted normally, speedometer rock steady, Hptuners logged the entire time. Must be on to something. Where I tapped into the wiring looked very solid. It was a painful splice to make near the connector, but the tape and wrap I used on it was still perfectly in place.

Time to see if it was my wiring or the gauge itself. I clipped the wires running to the gauge, leaving my splices as is. Plugged the yaw sensor connector back in and went for a long drive again. Car behaved perfectly, traction control back on, Hptuners logging the whole time. So, the problem is in the oil pressure gauge itself.

Now I have a functioning car again, but one non-functioning gauge. I shall bitch to Speedhut tomorrow about that. A car brought to it knees by a gauge. I will need a new gauge, but you can bet it will not be on the CAN bus. Independent sensor like the boost and AFR gauge.

Tweaker, thanks for planting the seed that reminded me that I had a gauge on the CAN bus. Otherwise it may have taken longer to track down with more parts thrown at it.

[Phil@PnP Tech]

No problem. I kinda figured it was bus related with all the symptoms.

[kevinm0131]

Dang, the might Blue Beast brought to its knees by a faulty gauge. Though I have a hard time saying that since you still ran a 10.19!
Glad you're on the right trail, electrical gremlins can be a real bitch to track down.

[2lazy4agoodname]

Glad you got it figured out!

[Doug Hilliard]

Great job getting it back up and functioning correctly!

[-Ray-]

It's only a matter of time.