Help Reading CEL Light

Mustang5L5 said:

If you go with the A3M you will definitely need ot check the O2 harness jumper and repin it.

Click to expand...

I’ll look into this, I gave the a3m a shot and after it warmed up I got a check engine light. When I attempt to pull any codes I just get a solid check engine light. Hmm…

Mustang5L5 said:

Not having it pinned correctly fries ECUs. You can’t stick a 5-spd ECU into an original AOD car without repinning it first.

Needs to match the below diagram based on year and ECU.



More info here

Electrical Thread 'O2 harness repin'

Jan 27, 2019

This thread is a HOW-TO for the process of repining the o2 sensor harness to match ECU/Trans, in the event the car is swapped. See post 15 as to what the jumper should be repinned to.

Step one. Remove the o2 sensor harness from vehicle. I find it easier to do on a bench plus it allowed me to degrease and reloom the harness. You can do this in the car if you want...it's that easy.

Here's the default loop setup in my 1988 AOD car


First you need to remove the red clip. Lightly pry up with a small pick


Next, look down inside with a light and you'll see small...

• Mustang5L5

Click to expand...

So I chose to go back with my ecu in the interest of time… I opened it up to see if I could see any bulging caps but everything looked ok.

If I would have read this before I decided to go with the original I would have given this a shot, I’ll try it another time.

Hopefully I didn’t fry the a3m I’ll open it up to make sure I didn’t fry the trace.

Update, sorry it takes so long to do things but im staying focused. I actually tried adjusting my brake booster pushrod and ended up having it to tight and the booster started leaking. i swaped it out for another used booster that turned out to be leaking as well. so i had to replace it with another booster and finally its not leaking.

I decided to repin the o2 harness to get the a3m working but i still had a solid check engine light and a solid light while pulling codes. I feel like i may have burned the ecu. I repinned it back for my a9l and called it a day. I did just get an innova code reader today to pull the intermittent code from my a9l. i got the same 15 and 94 and 44 with the koer. I will check to make sure air is getting to the cats when the engine is warm. I do have explorer heads so i dont have wholes for the thermactor tube. I just drilled and tapped screw wholes just to pass visual.

I am still stumped with the intermittent light at acceleration, and feel like the 15 memory code is way i cant read the codes. I think i will do a base idle reset, smoke test my intake and vacuum lines and maybe check my timing. I need to pass CA smog and would like to do it legit as it has passed smog twice before and the last time it passed with a seized smog pump.

AeroCoupe said:

If you do not have a chip on the ECU and you are getting a 15 it’s time to send it for repair.

Click to expand...

Im open to getting it repaired once i can get my other car up and running, in the meantime has anyone seen a schematic for the a9p or an a3m? to see if i indeed fried the a3m I will try to follow the traces from pin 1 on my a9p to see if i can find the problem on the board.