Car won't start, U0100, Bad ECM?!

[102SS]

Can you turn the fuse box over to inspect the wiring?

It seems like you have narrowed this down.

[Gunn]

Originally Posted by 102SS

Can you turn the fuse box over to inspect the wiring?

It seems like you have narrowed this down.

Spent an hour or two tonight and have a little more info to eliminate some areas, but still have not found the problem.

So I concentrated on the diagram attached and he Powertrain Relay, the 15A ECM fuse that keeps blowing, and the wiring to the ECM. The PNK/BLK wire eventually splits into 3 PNK/BLK wires and go into Pins 3, 5, 6 of the X2 Connector on the ECM.

I wanted to test if the wiring from the fuse box to the ECM connector had the short or not. I kinda was hoping it di as it's pretty short and right in the area of the fusebox in the engine compartment. But I couldn't energize the Powertrain relay without the fuse blowing.

I removed the X2 connector from the ECM. And I removed the relay and verified I had 12V battery power on 30 and 85 of the relay connectors in the fuse box. I then put in a jumper wire from 30 to 87. When I did this, the "left" leg (towards rear of car as looking from passenger fender) of the ECM fuse had 12V power. Cool, now I could check that harness to the ECM pins.

I checked for a short in that harness using an ohmmeter but didn't detect anything. So then I put in a new 15A fuse and crossed my fingers (actually hoping it would blow!). It didn't. It was fine. I then measured 12V power on pins 3, 5, 6 of the ECM x2 connector. I also checked for ground on pins 1,2 and 4 which did have a good ground. So those first 6 pins are all fine.

So that means the harness pertaining to that ECM fuse from battery, through fuse box, to the ECM is just fine.

Now what!??

One more thing. As I mentioned before, as soon as the door opens, the car comes alive and the fuse blows. I had my wife sit in car with the door closed until it went asleep. As soon as she slides the key into the ignition, the fuse blows. That must also wake up the car, same as opening the door. Clue?

And one more thing. With the key in the accessory or run position (fuse blow of course), we can move the power windows up and down. Put it up all the way. When the door is opened, as you all know the window opens ever so slightly. When you close the door, the window does NOT go back up. Clue?

That's all for today. Ughhhh. I'm really wondering if I need some super fancy $$$ scanners or tools or something to find this problem. Not sure where to go from here as I've looked over 120 pages of wiring diagrams and this is all I could find pertaining to this fuse, no other circuits. :(

Thanks all,

Tom

[silversleeper]

Originally Posted by Gunn

Spent an hour or two tonight and have a little more info to eliminate some areas, but still have not found the problem.

So I concentrated on the diagram attached and he Powertrain Relay, the 15A ECM fuse that keeps blowing, and the wiring to the ECM. The PNK/BLK wire eventually splits into 3 PNK/BLK wires and go into Pins 3, 5, 6 of the X2 Connector on the ECM.

I wanted to test if the wiring from the fuse box to the ECM connector had the short or not. I kinda was hoping it di as it's pretty short and right in the area of the fusebox in the engine compartment. But I couldn't energize the Powertrain relay without the fuse blowing.

I removed the X2 connector from the ECM. And I removed the relay and verified I had 12V battery power on 30 and 85 of the relay connectors in the fuse box. I then put in a jumper wire from 30 to 87. When I did this, the "left" leg (towards rear of car as looking from passenger fender) of the ECM fuse had 12V power. Cool, now I could check that harness to the ECM pins.

I checked for a short in that harness using an ohmmeter but didn't detect anything. So then I put in a new 15A fuse and crossed my fingers (actually hoping it would blow!). It didn't. It was fine. I then measured 12V power on pins 3, 5, 6 of the ECM x2 connector. I also checked for ground on pins 1,2 and 4 which did have a good ground. So those first 6 pins are all fine.

So that means the harness pertaining to that ECM fuse from battery, through fuse box, to the ECM is just fine.

Now what!??

One more thing. As I mentioned before, as soon as the door opens, the car comes alive and the fuse blows. I had my wife sit in car with the door closed until it went asleep. As soon as she slides the key into the ignition, the fuse blows. That must also wake up the car, same as opening the door. Clue?

And one more thing. With the key in the accessory or run position (fuse blow of course), we can move the power windows up and down. Put it up all the way. When the door is opened, as you all know the window opens ever so slightly. When you close the door, the window does NOT go back up. Clue?

That's all for today. Ughhhh. I'm really wondering if I need some super fancy $$$ scanners or tools or something to find this problem. Not sure where to go from here as I've looked over 120 pages of wiring diagrams and this is all I could find pertaining to this fuse, no other circuits. :(

Thanks all,

Tom

https://www.ebay.com/itm/25573753317...ke%3AChevrolet


It's not so expensive I'd be tired of all the hours of looking at some point and just try it.

[acutron42]

I agree with silversleeper. We hate just throwing parts @ problems but sometimes there is no other viable option. I am wondering if you have an issue in the BCM. There is alot going on in that little box as well. I would confirm a good ground from the BCM to the center console & trunk as well. Also, look for any corrosion in the connectors.

[102SS]

I think Acutron is on to something.

It seems to be on the Retained Accessory Power side of things causing your fuse to blow.

Electrical gremlins are the worst...good luck.

[gtstorey]

You could check and confirm no connection to any of the wiring that feeds the BCM from the shooting fuse, but the wake up is telling the ECM to come alive, so it could still be the ECM. I was doubtful at first, but I'm leaning that way now. I spent some time looking at wiring diagrams last night and didn't see anything downstream of the ECM that it is supplying primary power to.

[silversleeper]

I'm too lazy right now to fully think of all the diagrams. I would take a look at drivers door inout wiring at the hinge area as someone said just in case its broken shorted as related to bcm and all, however...
In general terms I'm feeling communication wiring even if shorted from the ecm to bcm I wouldn't think could BLOW a 15a fuse. Communication wiring I'd think carries little current. Just like when someone in this thread said they didn't suspect sensors shorting causing it. I'm in agreement. Sensor or their wires...
So I don't really know sooo much on all this but I'm in just guess mode that when the ECM gets a wakeup some internal diode sorta like a relay energises the computer and something really shorted to blow it.
The problem is I don't know sooo much so I can't really say for sure even if I study the heck out of the wiring. If it was me I'd look at those into door wires then start buyin' parts. That's also if the pulling relays I mentioned didn't find a bad circuit somehow related to this. With all these interconnected circuits, oh boy.

[gtstorey]

Very doubtful it's a com line issue. The voltage would be pulled to zero and they look good in the original post.

Most (probably all) of the ECM sensors reported can be shorted to ground without doing anymore than setting a DTC. You might consider confirming the various 5v references are actually at 5v and not pulled to 0. Unplug one of the sensors the diagrams indicate are tied to each of the 5v references and confirm voltage is correct. You only need to check one on each of the 5v circuits. I think there are 3. But I doubt that the 5v shorted to ground would shoot the fuse.

[acutron42]

That makes sense gt. This one is a head scratcher for sure.

[Gunn]

Alright, thanks for the all the comments and suggestions guys. I've been able to get out to the car and mess with it a bit more. More clues, but still no fix.

I've looked at the driver and passenger door wiring but it all looks very nice and clean. Plus, the driver door window, locks and trunk release all work. So I don't think there's a problem there.

I can't check for a 5V reference on any sensors since the ECM won't power up! Once the ECM tries to come alive via the powertrain relay and that 15A ECM Fuse, it immediately blows.

Since the powertrain relay is trying to energize the ECM when I either open the door or put the key into the ignition, I decided to go mess with the BCM circuitry and fuses based on some suggestions. First I removed ALL fuses, circuit breakers and relays from the Instrument Panel Fuse Block (driver side dash).

Put in a new 15A ECM fuse, all good. But of course, the car is basically dead. No power anywhere. In looking at the fuse diagram, there are fuses labeled BCM 1 - 8. BCM6 is in the underhood fuse box and is still there and is fine.

I figured those fuses should go back in first since all of the other accessory stuff probably wouldn't even work without them. So I started with "BCM 1" in position F25. Boom. The fuse immediately blew (I had the door open). Well that was fast. I removed it, replaced the ECM fuse and then was able to add BCM 2, 3, 4, 5, 7, 8 all without any problems. I re-added the relays and circuit breakers, no problem. At this point I decided to add in the rest of the accessory fuses (without F25, BCM1).

When I got to the very last one, F1 DLIS fuse ("Discrete Logic Ignition Switch"), a 5A fuse, boom! It blew again. I removed ALL of the fuses again, replaced the ECM fuse that blew in the engine compartment and then just added F1. Boom, it blew.

Bottom line, if ALL fuses are out and I add EITHER F1 DLIS or F25 BCM1, the ECM fuse blows.

I came back in, poured over the wiring diagrams but really couldn't find any real link. Obviously, either of these two fuses is triggering the ECM to ground out pin 86 on the powertrain relay (yellow wire, pin 58 of the ECM X2 connector) on the trigger side, which then tries to energize the load side containing the ECM fuse, which is then shorting out to ground. So I don't know how much help this is, since my issue must still be in that load side, of which the wiring diagrams show the wires ending up in the ECM (and I've proven the harness from fuse box to ECM is good for these wires in my previous post).

Attached are some wiring diagrams I found of these two fuses. I can't see anything helpful. I hope someone else can!

Thanks,

Tom

[gtstorey]

I think all you are getting is that the ECM is shooting a fuse every time it powers up.

[Seth21]

Originally Posted by Gunn

Understood. So you think that the ECM fuse blowing could be caused by something downstream of the ECM? I was kind of thinking it had to be something upstream of the ECM (harness to fuse box, and upward to battery voltage). If it's downstream, I'm not sure how to figure out what to look for. At that point, it could even be a sensor grounding out, and then...you're looking at a crap ton of stuff. Maybe a scanner could dig deeper (although if it can't communicate with the ECM...).

A refurb ECM is currently $420.00, and a 30% restocking fee if it doesn't work out and I need to return it. Return policy simply states "...part is in its original condition. Returns will undergo testing once received in our facility to confirm functionality." I may make that gamble...just to eliminate the ECM if it doesn't fix my problem immediately. :(

Hi I am Seth and I am new here forgive that, I have a extra core ECM that I am not using but you will still have to flash it with GM Software. The main issue your facing is the fact that not a single NEW ECM is available in most parts of the USA due to age. Recently My dad gave me two of his older toys 2010 and a 2011. Both had similar issues and the 2010 Lt shorted the Ecm and it was no longer readable by meter. Please let me know if your Ecm shows any codes still? If its not please don't rip up the dash any seeking the BCM. On both years there is a panel not very well known that harbors the communication Box on the left side dash in the very entrance to drivers side.
You will find some large relays there that are most likely your issue. Check the relays and very by meter that those big Fuses still ohm out. Most F-bodies have an additional two Fusible areas other than the obvious 1. Rear Right quarter panel inside the trunk 2. If you check the positive cable on the battery on the cable it self you will find a single Battery fuse "Looks like part of the cable but is removable and replaceable in the circuit. If you can find a ECM Great if Not let me know the number of your ecm and I will send you one just pay shipping ok . I can not flash your Vin but its a new core we bought from a seller online refurbed and I doubt I will ever use it. Problems with these cores as they use a NON GM software in an effort to save money and it may work for you the way it is but mot likely will need to be re flashed.

Let Me Know

Seth

[Seth21]

Originally Posted by Gunn View Post
Understood. So you think that the ECM fuse blowing could be caused by something downstream of the ECM? I was kind of thinking it had to be something upstream of the ECM (harness to fuse box, and upward to battery voltage). If it's downstream, I'm not sure how to figure out what to look for. At that point, it could even be a sensor grounding out, and then...you're looking at a crap ton of stuff. Maybe a scanner could dig deeper (although if it can't communicate with the ECM...).

A refurb ECM is currently $420.00, and a 30% restocking fee if it doesn't work out and I need to return it. Return policy simply states "...part is in its original condition. Returns will undergo testing once received in our facility to confirm functionality." I may make that gamble...just to eliminate the ECM if it doesn't fix my problem immediately. :(

Forgive my post as I had no idea the extent of your knowledge and most of my questions were answered, I just wanted to help because I have had the same experience and no one would help out, so I leaped before looking. BTW
The fuel rails are another bad source for a short. I wish you well

Seth

[Seth21]

Originally Posted by Gunn

Spent an hour or two tonight and have a little more info to eliminate some areas, but still have not found the problem.

So I concentrated on the diagram attached and he Powertrain Relay, the 15A ECM fuse that keeps blowing, and the wiring to the ECM. The PNK/BLK wire eventually splits into 3 PNK/BLK wires and go into Pins 3, 5, 6 of the X2 Connector on the ECM.

I wanted to test if the wiring from the fuse box to the ECM connector had the short or not. I kinda was hoping it di as it's pretty short and right in the area of the fusebox in the engine compartment. But I couldn't energize the Powertrain relay without the fuse blowing.

I removed the X2 connector from the ECM. And I removed the relay and verified I had 12V battery power on 30 and 85 of the relay connectors in the fuse box. I then put in a jumper wire from 30 to 87. When I did this, the "left" leg (towards rear of car as looking from passenger fender) of the ECM fuse had 12V power. Cool, now I could check that harness to the ECM pins.

I checked for a short in that harness using an ohmmeter but didn't detect anything. So then I put in a new 15A fuse and crossed my fingers (actually hoping it would blow!). It didn't. It was fine. I then measured 12V power on pins 3, 5, 6 of the ECM x2 connector. I also checked for ground on pins 1,2 and 4 which did have a good ground. So those first 6 pins are all fine.

So that means the harness pertaining to that ECM fuse from battery, through fuse box, to the ECM is just fine.

Now what!??

One more thing. As I mentioned before, as soon as the door opens, the car comes alive and the fuse blows. I had my wife sit in car with the door closed until it went asleep. As soon as she slides the key into the ignition, the fuse blows. That must also wake up the car, same as opening the door. Clue?

And one more thing. With the key in the accessory or run position (fuse blow of course), we can move the power windows up and down. Put it up all the way. When the door is opened, as you all know the window opens ever so slightly. When you close the door, the window does NOT go back up. Clue?

That's all for today. Ughhhh. I'm really wondering if I need some super fancy $$$ scanners or tools or something to find this problem. Not sure where to go from here as I've looked over 120 pages of wiring diagrams and this is all I could find pertaining to this fuse, no other circuits. :(

Thanks all,

Tom

Please find picture reference's I hope this will also help The old one smells so bad I have to keep in a bag in the garage, The new one that I will donate has the generic software and you now can see the error you can expect by buying a refurb. You can use it but you must have someone like a locksmith reprogram your keys to bcm even though they previously worked. This will start the car but will most likely give you the generic coding error still but the car will start. If you trust your nose detach the ECM from Terminals and Slide and take a good WIFF :))