I believe I have a dead ecu but I am not completely sure. When I hook up a OBD-II code reader the reader displays an error reading connection error but on a different car the code reader works properly.

2003 Honda civic auto dx

Some background:
I switched out my D17a1 for a D17a2(vtec)with an 02 ex ecu and 02 ex auto wiring harness
I did this swap a few months back because the short block went at 40k and might as well go vtec since both complete engines were $400 each for the the 40k mile range.

I also had to replace my alternator and battery and a few weeks after doing so my battery indicator light came on while I was driving. i checked my voltage which was good. 12.something engine off and 14.3 while the engine is running both at the alt and battery

Current problem:

I was at a red light and once the light turned green i gave my car gas and it revved to about 2500-3000 (estimate no rpm gauge) but would not shift to 2nd or go above 5mph at this same moment i noticed my battery light was no longer on(not sure if this is related or not). I was able to get it home since i was just down the street. I first thought it was a blown transmition since i was able to manually put it in d2 and d3 and once in those gears it wouldn’t switch into a greater gear but when i went to check what codes the ecu was throwing with a OBD-II code reader i experienced the reader displaying an error reading connection error but on a different car the code reader works properly. I was told by a Honda Tech that it was either the ecu or the connector/harness for what ever that is worth.

Any insight or knowledge would be greatly appreciated

 

Check whether 10A hood fuse 9 is blown.

 

Im sorry I forgot to mention that I checked all fuses with a multimeter. That is the under the hood fuse box as well as the fuses under the steering column

 

Hi, big fun you've got there. Nothing like sorting out electrical chaos.

For what it's worth ECUs seldom fail, I'm told the only way to destroy an ECU is to adapt in the wrong one, ha ha ha, no, not really, I think they require a fire to effect destruction.

The connections are far more suspect.

1) can you get the dash light to reveal the codes by shorting the connector (or whatever on an 02/03 mongrel) instead of using the scanning tool?

2) I'd start going through all the ecu wires to ensure they are going where they are supposed to go

3) but I'd look at the newer connections you made first

4) before all that I'd look elsewhere, that batt light seems like the key symptom it should not be lit when the charging system is ok, MCU??? But only if the MCU controls the charge light. Otherwise go through the circuit that controls that light. If it's any consolation the solution will be simple yet obscure.

5) one more thought, once upon a time, fords (?) used the unlit charge lamp as a ground path, a burned out charge lamp screwed things up, surely honda is not that dumb?

 

thank you very much for your response.

all the wiring to the ecu from the engine harness is good and i suspect the same with both the cabin harness and the dash harness since i did not make any alterations to those harnesses.

i will start looking into the battery light circuit as well as the MCU which i am not fimiliar with. Does anyone have any insight on the mcu and this circuit?

thanks again

 

Did you check for battery voltage at both top test tabs of the installed fuse?

 

I did not test with the fuse installed ill be sure to check that after work once I reinstall the ecu which i took out inorder to perform a visual inspection (No visual damage).

Also i had a spare engine harness that wires check out in terms of continuity but i have yet to hook it up to the battery or ecu.

 

i just realized while reading up on the MICU that it controls the ac which made me remember that the ac died at the very moment this all occured. i will check the fuse as well as check the MCIU and i will post my results.

thanks for the help so far

 

 

I have 12.7v on both sides of 10a fuse #9 via test tabs