Project Undertow #388

Dominicnicklyn

Dominicnicklyn

Active Member
So, found some weird info. We sorted through the pedal and other wires to insure we had them wired/in the correct place. We now have coms with everything except the EPS module.

We determined that the live data that we are getting with tech2win is being transmitted through the low speed GMLAN. As the EPS is the only module that doesn't have a low speed, we think that I have a high speed issue. It seems that none of the modules are talking properly on the high speed.

I don't know if this would be an ECM power/ground issue. Butterfly doesn't move and we have continuity through the high speed bus. Resistance is where it should be.

Help!
 
Dominicnicklyn

Dominicnicklyn

Active Member
Also for some weird reason, my dash only does the light check for the theft light when keyed on. (We disabled VATs already.)
Although when we keyed on and accidentally left the blue conector unplugged on the p12 ecm, the dash worked and all the lights did the safety check.

Even the seatbelt warning and abs lights stayed solid with the ecm plug disconnected. When plugged back in, the dash goes back to the 5 second theft light and only the fuel level works.
 
Dominicnicklyn

Dominicnicklyn

Active Member
So, I go out to the garage today after the long night of debugging. Trickle charger says battery is in the green and I have 13.2v.

I turn the key and with all the modules attached, the dash lights up and the butterfly moves. Awesome! Still no crank

I use tech2win to see that all the modules are communicating how they are supposed to. Then I key off and back on and the dash only displays the theft light for 5 seconds again and the butterfly doesn't move.

Battery dropped to 12.53v and now the car is back to where it was. I charge it back up past 13v and it fixes itself.

Ground issue? Battery seems to hold a charge on the 12v range with my lights and everything on.
 
Dominicnicklyn

Dominicnicklyn

Active Member
Gtstorey said:
I would probably start with a voltage drop test on every ground I could find.
Click to expand...
Any tips? Never done this before.

I'm starting to point my finger at the ECM power/ground. I have a small section of ground showing near the middle plug on my p12 ecm.

I also don't know how to take the plug apart to replace the wire (I will need to repin it due to the exposed wire being so close to the plug.)
 
G

Gtstorey

Goblin Guru
All of the grounds on the later model ECM’s are black with white stripes and all of the black with white stripes are ground. Likely the same on earlier models. So this is likely a problem. But may not be the only problem,

I’m not sure what this would have to do with charging the battery but may be some issue with ECM being asleep/awake instead of actually charging battery.

Those connectors are a serious pain to put back together if they are the same as the BCM connectors. All of the wires will come loose and getting them lined up is not easy. Can you solder an extension on?
 
Dominicnicklyn

Dominicnicklyn

Active Member
Gtstorey said:
All of the grounds on the later model ECM’s are black with white stripes and all of the black with white stripes are ground. Likely the same on earlier models. So this is likely a problem. But may not be the only problem,

I’m not sure what this would have to do with charging the battery but may be some issue with ECM being asleep/awake instead of actually charging battery.

Those connectors are a serious pain to put back together if they are the same as the BCM connectors. All of the wires will come loose and getting them lined up is not easy. Can you solder an extension on?
Click to expand...
I probably can, it will be tough but it's doable. I'll give it a shot
 
Dominicnicklyn

Dominicnicklyn

Active Member
Now If I let the car sit without the charger I can turn the key and get good results. But if I turn it off and try again within 30 sec it will go back to just the theft light check and no butterfly. Really weird.

I'm thinking a module isn't getting good ground.
 
G

Gtstorey

Goblin Guru
Could be a ground or other connection getting warm on first power up and then not passing enough current when warm. But sounds more like an ECM wake up/asleep issue.

Confirm the missing ground is actually a ground. Extend and connect to the lug with the other grounds. And make sure the other grounds are 100% clean and tight, including the post. And then check your ground on the battery end is 100% at the battery and frame connection.
 
Dominicnicklyn

Dominicnicklyn

Active Member
Gtstorey said:
Could be a ground or other connection getting warm on first power up and then not passing enough current when warm. But sounds more like an ECM wake up/asleep issue.

Confirm the missing ground is actually a ground. Extend and connect to the lug with the other grounds. And make sure the other grounds are 100% clean and tight, including the post. And then check your ground on the battery end is 100% at the battery and frame connection.
Click to expand...
Yeah, working on that currently. Just did another t2w test and it failed the ECM but I have coms with the EPS.
Our assumptions are starting to prove themselves.
 
G

Gtstorey

Goblin Guru
Did it connect to the bcm module? If the bcm isn’t getting power it might not wake the ECM up. And the BCM is next in line after the EPS.
 
Dominicnicklyn

Dominicnicklyn

Active Member
Gtstorey said:
Did it connect to the bcm module? If the bcm isn’t getting power it might not wake the ECM up. And the BCM is next in line after the EPS.
Click to expand...
Yes, everything else is working as it should. I did another test and it passed the ecm. Sometimes it fails, others it passes
 
G

Gtstorey

Goblin Guru
If you can see the bcm and eps all of the time, it’s time to get the wiring diagram and/or pin out for your ECM and confirm everything has power and ground everywhere you should when you have key on. If you are loosing both bcm and ECM at the same time, I would start check for a short to ground on the data wires.
Are you getting any trouble codes that tell you anything?
 
Ross

Ross

Goblin Guru
This sounds like some of the issues I was having. The solution to my goblin's issues was
1. poor connection on the connectors under the fusebox, (reseating the connectors fixed this)
2. bad data connector at the power steering (bought a connector from an auto recycle yard, soldered it on)
3. replaced the power steering unit with used one.
I also cleaned every ground wire and retorqued all 3 of my grounding points, which have a bunch of ground wires on each one.

When your data is flowing enough to move the throttle butterfly, I wonder if jumping the starter motor would allow it to run. On my LSJ, I ran the purple starter wire into the cabin, so I could connect it to accessory 12V power, and jump the starter quickly, while in traffic. I had to do this for about 6 months, as it took that long for me to debug my data issues.
 
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