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Author Topic: ECM Fuse Blown  (Read 9813 times)

Offline snagel

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ECM Fuse Blown
« on: January 08, 2009, 05:32:47 PM »
1999 Cadillac Escalade, thinking 5. 7 engine.

Driving down the road the other day and it shut down, gauges went crazy and simply died.   It would crank, but quickly the battery died.   Towed home and found the battery was "bad" (atleast this is what the guy at parts store said).   Battery was 6 years old; so, replaced with new battery.   Still would not start and found the fuse the the ECM blown.   Replaced fuse and started right up.

A week later, wife driving down road and same thing happened.   Rescued her and found the fuse to ECM blown again.   Replaced fuse, it started up and was able to drive it home.

So, now I'm thinking maybe the altenator may be bad.   Will have it checked out this weekend.   Any thoughts?  I'm thinking maybe the altenator is surging or something; which, destroyed first battery and sent a surge through system blowing fuse to ECM.   

If it is not this, not sure where to look next.   Sounds like I have a short somewhere, but strange it is only blowing fuse to ECM.

S.  Nagel

Online nickb2

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Re: ECM Fuse Blown
« Reply #1 on: January 08, 2009, 07:06:10 PM »
Had a similar problem once on a savana van. The problem went as such, The client would come to the shop with ecm #1 fuse blown. I replaced fuse and sent him on his way after checking his check engine light as it said his maf sens was open circuit. New fuse in place, drive around for awhile until engine and all readiness moniters are done. Truck fine! Comes back, 3 days later, same fuse blown, ecm#1. New fuse, same code, maf sensor open circuit. This time check wiring to maf, after fuse replacement. Everything ok. I am not happy at this point cuz I can't find a fault. So I change maf sensor saying it might be intermitent. He comes back a week later, same ecm fuse blown. Maf code. Fu#k!!! Check wiring diagram and locate what this fuse gives juice to. All the O2 sensors, map, maf,egr, and neutral switch. So I put an independant fuse on all these circuits and send him on his way. Comes back a week and half later, Check engine light on, O2 sensor b1 s1 circuit open, my home made fuse had blown. Ok here it is, when this o2 sensor would be on heater mode, and he would accelerate, the engine would lean to right and the heater wire would ground itself on heat shield bolted to body. Replaced o2 sensor as wiring is not repairable and made sure it was routed away from body. Never saw him for that problem again and came back for lots of other buisness after. Make sure what this fuse is feeding and check all related wiring before throwing parts at it. On your cady, sensibly same wiring for ecm. Might be a problem like the one I encountered!! ....x
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Offline snagel

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Re: ECM Fuse Blown
« Reply #2 on: January 08, 2009, 08:36:40 PM »
Thanks for the information. . . . . my worst nightmare is that a wire is grounding itself intermittantly.   This gives me something to look for thanks again.   It does make sense because both times it has stalled out on the highway, it was accelerating up a slight incline.

S.  Nagel

Offline NickD

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Re: ECM Fuse Blown
« Reply #3 on: January 09, 2009, 09:22:36 AM »
Good news is that the fuse is blowing and not the ECM.  Outputs both five and twelve volts, can be anywhere in the wiring harness, some guys don't put those back where they belong if you had work done under the hood, or can be an intermittent component.  I normally end up checking everything.

Offline crunch

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Re: ECM Fuse Blown
« Reply #4 on: January 09, 2009, 10:39:49 AM »

Which fuse box?
Which ECM fuse? 
ECM-B or ECM-1
Crunch
OEM parts only hurt one time Crunch said that.
Cheap after market stuff will bite you many times. My brother in law is learning that the hard way.

Offline snagel

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Re: ECM Fuse Blown
« Reply #5 on: January 09, 2009, 05:52:05 PM »
It's the fust box under the hood by the firewall.

20A fuse, ECM-B

No check Engine or Service Engine light is on.

I crawled under the truck tonight and really can't see any wiring that is looking "burnt" "bad" or "bare".   The only one that looks suspect is going into an O2 sensor on the front passenger side.   A tan wire looks suspect and that it might be shorting out on the casing of the O2 sensor.   Not sure how these things work, but turned key on and tried to short out wire on casing where it looks bad; thinking, if this is it, it would cause the fuse to blow.   However it doesn't.   Is there only voltage on this wire if the engine is hot - maybe.   I'm not saying this is the problem, but the only wire I can that looks suspect.

Snagel

Online nickb2

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Re: ECM Fuse Blown
« Reply #6 on: January 09, 2009, 06:20:50 PM »
Hey snagel, if that wire your talking about is the heater wire for the o2, than it will only short when ecm commands heater on. This heater is there to get the o2 working quicker on start up. ....x
When it don't work, hit it!!!


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Offline crunch

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Re: ECM Fuse Blown
« Reply #7 on: January 09, 2009, 06:40:06 PM »
It's the fust box under the hood by the firewall.

20A fuse, ECM-B

No check Engine or Service Engine light is on.

I crawled under the truck tonight and really can't see any wiring that is looking "burnt" "bad" or "bare".   The only one that looks suspect is going into an O2 sensor on the front passenger side.   A tan wire looks suspect and that it might be shorting out on the casing of the O2 sensor.   Not sure how these things work, but turned key on and tried to short out wire on casing where it looks bad; thinking, if this is it, it would cause the fuse to blow.   However it doesn't.   Is there only voltage on this wire if the engine is hot - maybe.   I'm not saying this is the problem, but the only wire I can that looks suspect.

Snagel

EMC-B fuse feeds fuel pump relay and fuel pump oil pressure switch and the computer.
Stick computer on a seperate inline fuse for testing.
First thing I would.
I would check amp draw on fuel pump and check wiring on fuel pump oil pressure switch.
Orange wire feeds fuel pump relay and oil pressure switch.
That can also be put on seperate inline fuse.

All data online sub will have the wiring diagrams for it if needed.

Let us know how it goes.
Crunch
Oil pressure switch can be unpluged for test.
OEM parts only hurt one time Crunch said that.
Cheap after market stuff will bite you many times. My brother in law is learning that the hard way.

Offline crunch

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Re: ECM Fuse Blown
« Reply #8 on: January 09, 2009, 06:45:17 PM »
Hey snagel, if that wire your talking about is the heater wire for the o2, than it will only short when ecm commands heater on. This heater is there to get the o2 working quicker on start up. ....x

O2 sensor heaters are on ENG-1 fuse.
Crunch
OEM parts only hurt one time Crunch said that.
Cheap after market stuff will bite you many times. My brother in law is learning that the hard way.

Offline snagel

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Re: ECM Fuse Blown
« Reply #9 on: January 09, 2009, 06:50:00 PM »
Thanks Crunch,

Where would I find the fuel pump oil pressure switch?

S.  Nagel

Offline crunch

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Re: ECM Fuse Blown
« Reply #10 on: January 09, 2009, 07:01:50 PM »
Rear center of engine right back of intake manifold.
Good Luck.
Crunch
OEM parts only hurt one time Crunch said that.
Cheap after market stuff will bite you many times. My brother in law is learning that the hard way.

Offline crunch

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Re: ECM Fuse Blown
« Reply #11 on: January 09, 2009, 07:10:51 PM »
Open pdf below.

[attachment deleted by admin]
OEM parts only hurt one time Crunch said that.
Cheap after market stuff will bite you many times. My brother in law is learning that the hard way.

Offline jay

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Re: ECM Fuse Blown
« Reply #12 on: January 09, 2009, 07:43:10 PM »
Had a similar problem once on a savana van. The problem went as such, The client would come to the shop with ecm #1 fuse blown. I replaced fuse and sent him on his way after checking his check engine light as it said his maf sens was open circuit. New fuse in place, drive around for awhile until engine and all readiness moniters are done. Truck fine! Comes back, 3 days later, same fuse blown, ecm#1. New fuse, same code, maf sensor open circuit. This time check wiring to maf, after fuse replacement. Everything ok. I am not happy at this point cuz I can't find a fault. So I change maf sensor saying it might be intermitent. He comes back a week later, same ecm fuse blown. Maf code. Fu#k!!! Check wiring diagram and locate what this fuse gives juice to. All the O2 sensors, map, maf,egr, and neutral switch. So I put an independant fuse on all these circuits and send him on his way. Comes back a week and half later, Check engine light on, O2 sensor b1 s1 circuit open, my home made fuse had blown. Ok here it is, when this o2 sensor would be on heater mode, and he would accelerate, the engine would lean to right and the heater wire would ground itself on heat shield bolted to body. Replaced o2 sensor as wiring is not repairable and made sure it was routed away from body. Never saw him for that problem again and came back for lots of other buisness after. Make sure what this fuse is feeding and check all related wiring before throwing parts at it. On your cady, sensibly same wiring for ecm. Might be a problem like the one I encountered!! ....x

How did you put the independent fuse in all the sensor circuits to find the culprit?

thanks, jay

Offline snagel

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Re: ECM Fuse Blown
« Reply #13 on: January 09, 2009, 08:26:44 PM »
This is starting to get a little over my head (I grew up on the old chevy small blocks with carbs). . . .

The relay is in the fuse block next to the fuse.   It clicks so, I'm assuming it probably is okay.   Not sure how to put an inline fuse to this.

How do you check the amp draw at the pump?  What should it be?

The computer, I'm assuming is under the dash, how do I find the wire going to the fuse block?

I'm not sure I know what the fuel pump oil pressure switch is.   Back behind the manifold is a square box with contacts inside.   It seems to do something kinda makes a pop sound when I put the fuse in and out.   There is also a tall skinny part that to me is an oil pressure switch and next to it is something clipped on the top of the engine that says sensor.   All this looks good, can't seem to find anything wrong with the wiring.

I'm starting to wonder if I have a problem with the pump.   

I hate these problems because I can start it up and everything runs fine.   The fuel pump comes on and delivers fuel (obviously).   I'm not getting any codes (atleast the check engine light is not on).   This is my wifes truck and she is scared to drive it until I find out why it is suddenly stalling out and blowing the fuse.   We drove it for a week with no problems after replacing the battery and fuse the first time.

I hate to just drop the tank and replace the pump and hope for the best.   But, it is kinda looking that way.

I know these are stupid questions, but bare with me.

S.  Nagel

Offline snagel

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Re: ECM Fuse Blown
« Reply #14 on: January 10, 2009, 04:53:47 PM »
I hate chasing ghosts. . . .

I checked the wiring going to the fuel pressure/oil pressure switch and it appears to be in good shape.   I went ahead and changed the oil pressure switch since it is a pain to get to even see the wiring.   (pretty sure this didn't solve much, but what the hell).   Drove it around town and on the highway for about an hour and no issues (made sure I had ample amount of 20 amp fuses).

My only thought here is that I have a wire that is grounding out somewhere intermittantly, but not sure where.   The only other option is that the fuel pump is goofing up intermittantly.   I guess well just have to drive it and see.   Right now it is driving and running fine.

I also drove it down and just for S&G's, had the altenator checked - thinking maybe the diode blew when the battery did and maybe it was back feeding the electric.   Altenator checked out fine.

Anyway, it's a wait and see thing right now.

S.  Nagel

 

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