Car won't start, U0100, Bad ECM?! - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Gunn · 10-13-2023, 06:31 PM

After replying on another thread, I realized mine took off in a different direction and so warranted a new post.

Camaro was running just fine and then poof, wouldn't start. No clicking from the starter, no nothing. I haven't touched the car in years, other than regular maintenance. Checked and even swapped the battery. No luck. Everything electrical seems to work, lights, interior chime, dash lights, etc. EXCEPT the fuel gauge reads empty (it has just over 1/2 tank). Also shows "Service stabilitrack" errors and occasionally says to "Open, then close passenger window" and same with driver window. Once I open a door and the window lowers slightly, it won't raise back up.

Check engine light flashes like crazy (~5Hz) as soon as the key is turned to the ON position. Code reader shows U0100.

My first thought based on searches in this forum and elsewhere was to check for a bad ground. I downloaded a service manual. I removed all of the ground connections in the engine bay, cleaned them with a wire wheel on a drill and reinstalled (even removed paint from under body mount locations):

G101 - Rt. front lower on body (cleaned)
G102 - Rt. front lower on body, behind G101 (under heat shroud) (cleaned)
G103 - Rt front body, larger under fuse box (cleaned)
G106 - Rt. side engine in front (cleaned)
G108 - Rt. side engine, back (cleaned)

After each one, I tried to start the Camaro; no luck. Then I found that I should check the CAN bus. On the OBDII connector, I checked:

Pin 4 to pin 6 (can bus hi, key on): 2.67V (should be ~2.7V)
Pin 4 to pin 14 (can bus low, key on): 2.31V (should be ~2.3V)
Pin 6 and 14 (battery disconnected): 60.9 ohms (should be 60 Ohms)

So all that checks out good. Then I thought about the fuses. I went through the Service Manual and noted any fuse that mentioned ECM. The very first one I checked, fuse 5 in the engine compartment fuse block, aa 15A fuse for the ECM, was blown.

When I replaced it, I noticed the check engine light was no longer flashing. And my fuel gauge was back! Turned the key to the Start position and it cranked! However, it would NOT start. Bummer. Checked the fuse. Blown.

I found that as soon as I move the key to the On position, the fuse blows. And sometimes, the fuse will blow without ever moving the key from Off. But now my fuel gauge is fine, otherwise same original issues.

The wiring diagram for this fuse doesn't show much. Hot power goes from the "Powertrain Relay", through the fuse and then splits into 3 (J110) and are Pins 3, 5 and 6 of the ECM (labeled IGN VOLT, page 340 of service manual).

Are all signs pointing to a bad ECM? I'm thinking of buying a new one at www.allcomputerresources.com , but don't wan't to just throw parts at it (especially $400 parts0. But not sure what else to try?

I don't know how to test further, any ideas?

Thanks all,

Gunn · 10-13-2023, 06:32 PM

One more thing: Whenever I open up the drivers side door (key out of ignition), I'll hear a 3-4 second series of about 10 clicks from the engine compartment fuse block / ECM area in the front passenger side. I don't recall if I ever heard this before when things were normal. Not sure if it's a relay or the ECM itself. Maybe a clue? What is it? If anyone can tell me what this is, I'd love to hear.

102SS · 10-14-2023, 06:49 AM

My G8 LY7(3.6L) makes those noises.

It sounds like relays/solenoids clicking or something like that.

My V8 Camaro does not

hesster · 10-14-2023, 09:24 AM

Assuming your Battery is fully charged, it would seem that you have a SHORT somewhere in your wiring, because you are blowing the fuse repeatibly. A PIA, but inspect all wire harness for chafing, rub through, etc. Esp wires at the ECM. There are threads on the forum and I think a bulletin on harness wires shorting due to rubbing on stuff. The ECM ground is a poor design.
I bet if you replace the ECM, it may not solve your issue.
Maybe something in Post #9 may help.
My issue was a crap tune, not any wiring issues. But at least I have clean grounds now.
https://www.camaro5.com/forums/showthread.php?t=618251

Gunn · 10-14-2023, 07:08 PM

Quote:

Originally Posted by hesster

Assuming your Battery is fully charged, it would seem that you have a SHORT somewhere in your wiring, because you are blowing the fuse repeatibly. A PIA, but inspect all wire harness for chafing, rub through, etc. Esp wires at the ECM. There are threads on the forum and I think a bulletin on harness wires shorting due to rubbing on stuff. The ECM ground is a poor design.
I bet if you replace the ECM, it may not solve your issue.
Maybe something in Post #9 may help.
My issue was a crap tune, not any wiring issues. But at least I have clean grounds now.
https://www.camaro5.com/forums/showthread.php?t=618251

Yes, I have made sure the battery is fully charged. In fact, it's on a charger now in trickle mode just to keep it topped off. After charging, I tested the battery which tested good and more CCA than advertised. So it's good. Battery terminals themselves are nice and clean, along with the ground wire on the trunk floor.

I did the same as you and found and inspected all ground wires. I was hoping that was my issue at first so I removed all of them, cleaned them, even removed paint from the inner frame rail where the ground wires were and reattached with some dielectric grease to keep away the corrosion. None of that helped. And then I found the fuse blown. So now my problem is an inadvertent ground, instead of a bad one! Don't know if it's in the wiring harness or inside the circuit board of the ECM.

I haven't really figured out how to test the ECM yet. But there are plenty of people who have had bad ECM's, so I may go that route and buy a new one. Worst case is it doesn't do anything and I can return it for a 30% restocking fee, not the end of the world (www.allcomputerresources.com). Then I'll know it's either a wiring harness issue.

I'm going to keep messing with the wiring harness tomorrow, looking for any issues. But according to the service manual, the pathway from the fuse box to the ECM is pretty short and I haven't found anything obvious.

Thanks,

silversleeper · 10-15-2023, 09:22 AM

Quote:

Originally Posted by Gunn

I haven't really figured out how to test the ECM yet. But there are plenty of people who have had bad ECM's, so I may go that route and buy a new one. Worst case is it doesn't do anything and I can return it for a 30% restocking fee, not the end of the world (www.allcomputerresources.com). Then I'll know it's either a wiring harness issue.

Thanks,

Normally electrical parts are NOT returnable if you have opened them, broken the seals and installed them. Not for any fee of restocking.
I don't think an unprogrammed ecm will start or work I assume you know this?
An ecm from a crashed car might be for you but if you need to use dealer to program then they WON'T work with your used part and want $$$$ for a new part plus plus

gtstorey · 10-15-2023, 10:45 AM

The ECM from the OP link probably comes preprogrammed, if not there are other online places that will program them. But they may not be 100% plug and play. May have to do key relearn, immobilizer relearn etc.

But I doubt that is the problem. More likely to be a damaged harness somewhere.

acutron42 · 10-15-2023, 01:35 PM

Quote:

Originally Posted by gtstorey

The ECM from the OP link probably comes preprogrammed, if not there are other online places that will program them. But they may not be 100% plug and play. May have to do key relearn, immobilizer relearn etc.

But I doubt that is the problem. More likely to be a damaged harness somewhere.

These ones are very difficult to diagnose on a forum & does sound like a harness issue. What happens if you replace fuse 5 & don't put the key in. If it does not blow, maybe its in the switch but still hard to tell. That U0100 is probably the blown fuse loosing communication between the ecm & scan tool. This will stay in history until there are a certain number of successful key cycles.

Gunn · 10-15-2023, 10:25 PM

Quote:

Originally Posted by acutron42

These ones are very difficult to diagnose on a forum & does sound like a harness issue. What happens if you replace fuse 5 & don't put the key in. If it does not blow, maybe its in the switch but still hard to tell. That U0100 is probably the blown fuse loosing communication between the ecm & scan tool. This will stay in history until there are a certain number of successful key cycles.

If I replace Fuse 5 and don't put the key in, it's fine, does not blow.

If I disconnect the ECM x1 and x2 plugs, the fuse is fine in all key positions. If I connect the big (98 pin) x1, the fuse is fine in all key positions.

The harness from fuse box to ECM is short. It all looks fine, and I've looked in detail.

Oh and yes, the link I gave is to a fully programmed ECM with no re-learning necessary for anything, including immobilizer. And the 30% restocking fee is even if it was attempted to be used; I assume that's why it's so high.

Thanks,

chevy pilot · 10-16-2023, 02:14 AM

You haven't washed the engine room with a pressure washer ?

hesster · 10-16-2023, 07:28 AM

I considered this as a aid to resolve my starting issue.
https://www.camaro5.com/forums/showthread.php?t=539796

gtstorey · 10-16-2023, 07:51 AM

The problem with the ECM replacement route is it could be something after the ECM that is shorting. At least I've seen something after a BCM cause a power feed to the BCM cause a fuse to shoot.

Gunn · 10-16-2023, 07:52 AM

Quote:

Originally Posted by chevy pilot

You haven't washed the engine room with a pressure washer ?

No, never have.

Quote:

Originally Posted by hesster

I considered this as a aid to resolve my starting issue.
https://www.camaro5.com/forums/showthread.php?t=539796

I had seen that thread and watched the videos when all of this first went down. I'm going to watch again right now, thanks.

Gunn · 10-16-2023, 08:05 AM

Quote:

Originally Posted by gtstorey

The problem with the ECM replacement route is it could be something after the ECM that is shorting. At least I've seen something after a BCM cause a power feed to the BCM cause a fuse to shoot.

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. :(

10-13-2023, 06:31 PM	#1
Gunn 2011 Camaro LT V6 Drives: 2011 Chevrolet Camaro LT (V6) Join Date: Oct 2019 Location: Maryland Posts: 42	Car won't start, U0100, Bad ECM?! After replying on another thread, I realized mine took off in a different direction and so warranted a new post. Camaro was running just fine and then poof, wouldn't start. No clicking from the starter, no nothing. I haven't touched the car in years, other than regular maintenance. Checked and even swapped the battery. No luck. Everything electrical seems to work, lights, interior chime, dash lights, etc. EXCEPT the fuel gauge reads empty (it has just over 1/2 tank). Also shows "Service stabilitrack" errors and occasionally says to "Open, then close passenger window" and same with driver window. Once I open a door and the window lowers slightly, it won't raise back up. Check engine light flashes like crazy (~5Hz) as soon as the key is turned to the ON position. Code reader shows U0100. My first thought based on searches in this forum and elsewhere was to check for a bad ground. I downloaded a service manual. I removed all of the ground connections in the engine bay, cleaned them with a wire wheel on a drill and reinstalled (even removed paint from under body mount locations): G101 - Rt. front lower on body (cleaned) G102 - Rt. front lower on body, behind G101 (under heat shroud) (cleaned) G103 - Rt front body, larger under fuse box (cleaned) G106 - Rt. side engine in front (cleaned) G108 - Rt. side engine, back (cleaned) After each one, I tried to start the Camaro; no luck. Then I found that I should check the CAN bus. On the OBDII connector, I checked: Pin 4 to pin 6 (can bus hi, key on): 2.67V (should be ~2.7V) Pin 4 to pin 14 (can bus low, key on): 2.31V (should be ~2.3V) Pin 6 and 14 (battery disconnected): 60.9 ohms (should be 60 Ohms) So all that checks out good. Then I thought about the fuses. I went through the Service Manual and noted any fuse that mentioned ECM. The very first one I checked, fuse 5 in the engine compartment fuse block, aa 15A fuse for the ECM, was blown. When I replaced it, I noticed the check engine light was no longer flashing. And my fuel gauge was back! Turned the key to the Start position and it cranked! However, it would NOT start. Bummer. Checked the fuse. Blown. I found that as soon as I move the key to the On position, the fuse blows. And sometimes, the fuse will blow without ever moving the key from Off. But now my fuel gauge is fine, otherwise same original issues. The wiring diagram for this fuse doesn't show much. Hot power goes from the "Powertrain Relay", through the fuse and then splits into 3 (J110) and are Pins 3, 5 and 6 of the ECM (labeled IGN VOLT, page 340 of service manual). Are all signs pointing to a bad ECM? I'm thinking of buying a new one at www.allcomputerresources.com , but don't wan't to just throw parts at it (especially $400 parts0. But not sure what else to try? I don't know how to test further, any ideas? Thanks all, __________________ 2011 Camaro LT (V6)

10-13-2023, 06:32 PM	#2
Gunn 2011 Camaro LT V6 Drives: 2011 Chevrolet Camaro LT (V6) Join Date: Oct 2019 Location: Maryland Posts: 42	One more thing: Whenever I open up the drivers side door (key out of ignition), I'll hear a 3-4 second series of about 10 clicks from the engine compartment fuse block / ECM area in the front passenger side. I don't recall if I ever heard this before when things were normal. Not sure if it's a relay or the ECM itself. Maybe a clue? What is it? If anyone can tell me what this is, I'd love to hear. __________________ 2011 Camaro LT (V6)

10-14-2023, 06:49 AM	#3
102SS waiting at the tree Drives: SIM 2010 2SS/RS A6 Join Date: Apr 2013 Location: Niagara Falls Posts: 3,132	My G8 LY7(3.6L) makes those noises. It sounds like relays/solenoids clicking or something like that. My V8 Camaro does not __________________ 2010 2SS/RS A6 ZL1 Rims 60ft 2.03 13.08 at 107.82 (4/28) 2009 Pontiac G8 3.6L the DD

10-14-2023, 09:24 AM	#4
hesster Drives: '10 C5 SS, '77 Bandit T/A Join Date: Dec 2015 Location: Michigan Posts: 633 View My Garage	Assuming your Battery is fully charged, it would seem that you have a SHORT somewhere in your wiring, because you are blowing the fuse repeatibly. A PIA, but inspect all wire harness for chafing, rub through, etc. Esp wires at the ECM. There are threads on the forum and I think a bulletin on harness wires shorting due to rubbing on stuff. The ECM ground is a poor design. I bet if you replace the ECM, it may not solve your issue. Maybe something in Post #9 may help. My issue was a crap tune, not any wiring issues. But at least I have clean grounds now. https://www.camaro5.com/forums/showthread.php?t=618251

10-15-2023, 10:45 AM	#7
gtstorey Drives: 2010 Camaro SS2,L99, LSA SC Join Date: Aug 2017 Location: Huntsville, AL Posts: 2,147	The ECM from the OP link probably comes preprogrammed, if not there are other online places that will program them. But they may not be 100% plug and play. May have to do key relearn, immobilizer relearn etc. But I doubt that is the problem. More likely to be a damaged harness somewhere.

10-16-2023, 02:14 AM	#10
chevy pilot Drives: 2010 2SS/RS A6 Join Date: May 2019 Location: Hki.Finland Posts: 949	You haven't washed the engine room with a pressure washer ?

10-16-2023, 07:28 AM	#11
hesster Drives: '10 C5 SS, '77 Bandit T/A Join Date: Dec 2015 Location: Michigan Posts: 633 View My Garage	I considered this as a aid to resolve my starting issue. https://www.camaro5.com/forums/showthread.php?t=539796

10-16-2023, 07:51 AM	#12
gtstorey Drives: 2010 Camaro SS2,L99, LSA SC Join Date: Aug 2017 Location: Huntsville, AL Posts: 2,147	The problem with the ECM replacement route is it could be something after the ECM that is shorting. At least I've seen something after a BCM cause a power feed to the BCM cause a fuse to shoot.