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Daniel Wilson
Daniel Wilson,
Category: Chevy
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When my 2001 suburban warms up and goes into closed loop it

Customer Question

when my 2001 suburban warms up and goes into closed loop it blows the ecm fuse
JA: Do all the fuses have the correct amperage for the circuits they're in?
Customer: yes
JA: Are you fixing your Suburban yourself? What have you tried so far?
Customer: yes. I disconnected bank one O2 sensor one and it quit blowing the fuse. I replaced the O@ sensor and it is blowing the fuse again.
JA: Anything else you want the mechanic to know before I connect you?
Customer: no, thats it
Submitted: 14 days ago.
Category: Chevy
Expert:  Ron replied 14 days ago.

Hello. My name is ***** ***** I am happy to assist you today. Give me just a moment to review your post, and I'll be right back with the help you need.

Expert:  Ron replied 14 days ago.

Is this the ECM B fuse?

Customer: replied 14 days ago.
ECM B, 20 amp
Customer: replied 14 days ago.
no calls thank you.
Customer: replied 14 days ago.
originally I was told by the dealer it was a bad computer, a new one was installed and flashed and it still blows fuses.
Expert:  Ron replied 14 days ago.

Okay the most common cause for the ECM B fuse to blow is in most cases caused by excessive amp draw from a failing fuel pump . In order to determine if in fact that is the cases you are going to need to do some testing while the problem is present. I have enclosed the steps to do this in the link below.

https://dl.dropboxusercontent.com/u/104923897/ECM%20fuse%20B%20Nov%2026.pdf

Expert:  Ron replied 14 days ago.

Let check the fuel pump first as its a very common cause for this fuse to blow.

Customer: replied 14 days ago.
The fuel pump has been replaced. When I disconnected O2 sensor bank one O2 sensor one it quit blowing the fuse, so that would eliminate the fuel pump.
Expert:  Ron replied 14 days ago.

If you dealing with the ECM B fuse then the HO2S sensors are not on that circuit. Are you sure its the ECM B fuse?

Customer: replied 14 days ago.
no, I'me a disabled Veteran living on a fixed income.
Customer: replied 14 days ago.
it is ECM B fuse, it is the 20 amp fuse right
Expert:  Ron replied 14 days ago.

The HO2S sensors use the ECM one fuse and if thats the fuse that blowing and stops blowing when you disconnect the bank one HO2S sensor then that would point towards a failing HO2S sensor. Need to know for sure which fuse is blowing.

Customer: replied 14 days ago.
Its the 20 amp fuse.
Expert:  Ron replied 14 days ago.

Yes the ECM B fuse is the 20 amp fuse, one other thing on that circuit that could be shorting could be the orange power feed wire to the ECM (computer). That being said, the most common cause for this fuse to blow is a failing fuel pump or the wiring to it.

Customer: replied 14 days ago.
If that was the cause why did the fuse not blow when I disconnected the bank one O2 sensor one.
Expert:  Ron replied 14 days ago.

That I am not sure of but if you have the right fuse and it holds with the HO2S unplugged then perhaps is affecting the ECM and causing the fuse to blow. If its hold with this sensor unplugged then that points to a shorted HO2S. Did you try replacing it and see if the fuse still holds?

Customer: replied 14 days ago.
The fuel pump is powered up when the engine is started, but the fuse only blows when it goes into closed loop.
Customer: replied 14 days ago.
I replaced the O2 sensor and it still blows
Expert:  Ron replied 14 days ago.

Have a look at the enclosed wiring diagram for the ECM B fuse, you will see the only things on that circuit is the ECM, fuel pump and transmission control module. The O2 sensor is not on this circuit.

https://dl.dropboxusercontent.com/u/104923897/ECM%20B%20wiring%20Nov%2026.pdf

Customer: replied 14 days ago.
I see what you mean, I have a copy of this wiring diagram from the dealer. I'm stumped thats why I was asking you.
Expert:  Ron replied 14 days ago.

Okay can you get it into closed loop and pull the fuel pump relay and see if the fuse holds?

Customer: replied 14 days ago.
Will the engine run without the fuel pump relay. If a O2 sensor is disconnected will the computer still go into closed loop?
Expert:  Ron replied 14 days ago.

No it will not but if the fuse holds then that points to a failing fuel pump and or the power feed to it. If the fuse blows with the relay out then I would have a look at the orange power feed from the fuse to the pin 57 at the computer.

Customer: replied 14 days ago.
I'm convinced the fuel pump is good because when it goes into closed loop the fuse blows. I replace the fuse and I can drive it all day and it does not blow again until it sits overnight and I start it the next day and blows again when it goes into closed loop.
Expert:  Ron replied 14 days ago.

Well it has to be something on that circuit. Its just a matter of narrowing it down.

Customer: replied 14 days ago.
I'm back to square one. I don't know any more than I did when we started this conversation.
Expert:  Ron replied 14 days ago.

Okay I will open the post back up for you, perhaps someone else has something new to add.

Customer: replied 14 days ago.
I'm not satisfied at all, I was never told anything I did not already know and my problem was never solved.
Expert:  Tim's Auto Repair replied 14 days ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you.

it always blows the same ecm fuse?

Customer: replied 12 days ago.
Sorry Tim, since we have not communicated yet I can not rate you. Ron tried to help but could not, he only told me what I already knew and kept asking the same questions over and over, it was as if he had not read my post at all. I hope you can do better.
The problem began early this year on my 2001 Suburban 5.3 that has over 225,000 miles. When I drive the vehicle for the first time each day, at the instant when all the parameters are met, IE the engine reaches operating temperature and signal is received from the HO2 sensors and the appropriate amount of time has elapsed and the computer goes into closed loop, the 20 amp ECM B fuse will blow. At that time I replace the fuse, the engine starts and I can drive it all day running errands, shutting off the engine, restarting and so on for the rest of the day without the fuse ever blowing again. Only after ant the end of the day I get home park the Suburban let it sit overnight then the next day it starts all over again. I went to the Gunn Chevrolet dealership in Schertz Texas and the service technician said it was the computer. I bought a new computer and had them install it and flash it. This did not solve the problem. Ron said it was the fuel pump, I already replaced the fuel pump. If its the fuel pump how do you explain that after the fuse blows when it goes into closed loop and I replace the fuse it runs all day long and never blows again until the next day.
Expert:  Tim's Auto Repair replied 12 days ago.

it does sound as if you have a bnad fuel pump,,the pump is pulling too many amps,perhaps the pump motor is just bad..

if you have just replaced the pump it should be under warranty..

replace that pump with another one

thanks

Expert:  Tim's Auto Repair replied 12 days ago.

the pump is getting hot and pulling too manyamps when hot,that is why it will run for a while after you replace the fuse

Expert:  Tim's Auto Repair replied 12 days ago.

If you are satisfied with my answer, Please Rate my answer by clicking the rating button so I can get credit for my work. I’m not always going to be giving you good news, so please don't let this stand in the way of you accepting my answer. .it does not cost you more money and we will still be able to communicate, ,.please understand, i can not see, hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated.. if you are not satisfied with my answer, please do not leave bad feedback ,i will gladly opt out and let another expert handle the question. .if i have sent any diagrams, please print them. .sometimes you may need to right click the image [,then save picture as]to save it to your computer so you can open it with your picture program...Please ask if you need more help.

Customer: replied 11 days ago.
No I'm not satisfied with your answer. I do not believe in troubleshooting by replacing parts. I halfway expected you to at least recommend checking the amperage on the pump before replacing it. I tested the amperage draw and it is 5.47 amps, hardly enough to blow a 20 amp fuse. To remove all doubt I installed a ten amp fuse in the pump circuit. The 20 amp fuse blew and the 10 amp fuse in the fuel pump circuit did not. In my original post I explained in great detail how the fuse will blow when the computer switches to closed circuit and does not blow the rest of the day. I hardly think you are qualified to be giving automotive repair advice, I would like to recommend a career in flipping burgers or perhaps delivering pizza. I'm not satisfied and expect a full refund..
Expert:  Tim's Auto Repair replied 11 days ago.

ok

Expert:  Daniel Wilson replied 11 days ago.

Hi My name is***** see you got a lot of free pizza. Thank you for your service. I hope you get this resolved.

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