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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8622
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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I was replacing the multi fuel injection relay, and now my

Customer Question

I was replacing the multi fuel injection relay, and now my ECU has no power, my diagnostic can not read the ECU.
Submitted: 2 years ago.
Category: Mitsubishi
Expert:  Doug replied 2 years ago.
Hi,
Do you have power on the OBD port on pin 16?
Customer: replied 2 years ago.
no
Expert:  Doug replied 2 years ago.
Thanks please go to the in dash fuse panel and check the following 15A fuse both to see if it blown AND to see if there is supply voltage there:

//f01.justanswer.com/ref/http_i.imgur.com/hTdATsC.png
Customer: replied 2 years ago.
signed up for a phone call. waiting for a response.
Expert:  Doug replied 2 years ago.
Sorry I am not available for a phone call right now. Are you able to inspect that fuse I indicated?
Customer: replied 2 years ago.
there is no power
Expert:  Doug replied 2 years ago.

Thanks. If the fuse I highlighted is good AND has power going through it, please go back and double check the pin 16 (white wire with a black stripe) to see if there is power there. You should have power if the fuse is good and powered, as it is a direct feed to that pin.

Expert:  Doug replied 2 years ago.
Crud, I apologize I misread that.
Customer: replied 2 years ago.
sorry I was saying yes I checked it, however there was no power.
Expert:  Doug replied 2 years ago.
No problem, my fault for reading it wrong :)
Please go to the under hood fuse panel and check link #1 which is a 60A link. Verify power at and exiting the link (the lens pops off the top for better access.

//f01.justanswer.com/ref/http_i.imgur.com/TAP2eDT.png
Customer: replied 2 years ago.
there is power
Expert:  Doug replied 2 years ago.
Hmm.
Lets go back to that fuse #15 and pull it out again and recheck to make certain there is no power there. The reason being there isn't anything in between that should cut power between them.
Nothing else was done except the relay work before right? Nothing else unplugged/dismounted/etc?
Customer: replied 2 years ago.
just rechecked, there is definitely no power at #15, and you are correct, there was nothing else unplugged or dismounted.
Customer: replied 2 years ago.
does the front ECU have anything to do with the MFI relay?
Expert:  Doug replied 2 years ago.
Hmmm.
That is pretty weird... Please go to connector C116 shown below, unplug it and check for corrosion in it, then if it is clean check to see if there is power on pin 15, which is a Red wire in the center of the connector (there is a stack of three larger pins in the center, it is one of those).

//f01.justanswer.com/ref/http_i.imgur.com/bQDGENl.png
Yes, the ecu is powered up by the MFI relay.
Customer: replied 2 years ago.
I'm receiving power from the red wire, also I checked fuse #15, and there is power, but only from one side to ground. When I check both sides of fuse #15, there is no power.
Expert:  Doug replied 2 years ago.
Okay, that changes things. If you put your meter between ground and each pin on the top of fuse #15, does one have power and one does not?
Customer: replied 2 years ago.
That's correct.
Expert:  Doug replied 2 years ago.
Great.... lets get that fuse out of there and put a fresh one in and see if you have power on both tabs now.
Customer: replied 2 years ago.
The fuse is good. When I checked it the first time I remove the fuse that why I was getting reading from only one side.
Expert:  Doug replied 2 years ago.
Oh okay... so both tabs of the fuse do have power then?
We are back to what I mentioned before then, lets recheck pin 16 white/b;ack wire on the obd port.
Customer: replied 2 years ago.
I have power at pin #16.
Expert:  Doug replied 2 years ago.
Okay, so that was a long detour!
Moving on... Please check under hood fuses #9 (20A) and #24 (15A) using my chart below:

//f01.justanswer.com/ref/http_i.imgur.com/JSb0YPM.png
Customer: replied 2 years ago.
Both fuses are good.
Expert:  Doug replied 2 years ago.
Thanks.
When you were changing the MFI relay, are you certain you got it back in the right location?
It should be in the standalone relay panel (the narrow row of relays in its own box underhood), and should be the second from the rear. Starting at the windshield you should have the AC clutch relay, then the MFI, then the transmission relay and the remaining sockets toward the front empty.
Customer: replied 2 years ago.
all the relays are in the right place
.
Expert:  Doug replied 2 years ago.
I'm at a loss then; If all that was done was the MFI relay being replaced and nothing else was unplugged/damaged/etc, your only real possibilities are the relay being bad, being put in the wrong spot, or a fuse failed. All fuses check out and the relay is in the right spot... can we try swapping a different relay in its place (horn relay or other one you can confirm works)?
Customer: replied 2 years ago.
I done that. Do you think the ECU could be bad?
Expert:  Doug replied 2 years ago.
Its certainly looking that way... the way you worded though was that you replaced "relay, now my ECU has no power..." Is it possible you had no power to begin with? As that would definitely change the entire scenario.
Customer: replied 2 years ago.
I had power before because I started it up once I replaced the relay. I pulled the relay out when it was running thinking it was the AC relay. I tried restarting but could not.
Expert:  Doug replied 2 years ago.
Yeah if those fuses are all good the only thing I can see that could have happened was a back feed through the ground signal socket of the relay. This is a direct feed to the ecu, and if 12V happened to go to it, that would burn out the ground driver inside the ecu, resulting in the MFI relay no longer engaging.
I don't really see anywhere else to go with this, given the test results and the order of events.
If this is the case, a new (or used) ecu is the way to go; these are not VIN coded, and being a 2003 it is likely to not have immobilizer either... if the key is flat metal or a "D" shape, it does not have immobilizer and the ecu can be freely swapped. If it is a late 03 with the narrow shield shaped key, then it has immobilizer and requires key programming when changing it out. You may be able to find someone to send it off to for repair as well.
Customer: replied 2 years ago.
Okay, Thanks!! I will look for an ECU tomorrow.
Expert:  Doug replied 2 years ago.
You're welcome, good luck!