04 blue civic

My friend has an ecm from his 04 last three digits of his is a73 where mine is a72. Dbesides having a locksmith program immobilizer does the ecm have to be programmed to car?

ezone

Gauges passed self test, battery light flashed during test?

Disconnect alt plug....key on (engine off)
have 12v @blk/yel wire? (fuse is ok)

Disconnect PCM
Have continuity from wht/blu to PCM-B10?
No continuity to ground on same wire? (no short to ground)

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What I really hate is this is the end of the troubleshooting tree, it sends you into checking the alternator. .....no mention of checking PCM or MICU, not that there's any easy way to check either of those without playing swaptronics.
Here's what I'd be checking at this point:

Reconnect PCM and alternator. Start engine.
Warning light on or off now? I'll assume it's still ON.

Turn engine off.
Disconnect alternator 4 wire plug again.
Key ON (engine off)
Battery Light is still on?
Measure voltage on wht/blu wire in the alt plug....You should see 5v. Do you have 5v on that wire?

Now use a jumper wire to connect wht/blu to ground.... and see if the warning light turned off.


Reasoning: White/blue is the alternator "L" terminal ("L" stands for 'light'), it internally grounds when the alternator is not charging.
In a conventional system that would supply ground to the warning light...but in this car it connects to the PCM instead of direct to the warning light.....so that's why I ask to see if it has 5v on the wire from the PCM, and see what happens when you ground it manually.

Moving on the MICU, did I ask if the car exhibits any other electrical oddities/problems?

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What was wrong with the friends used PCM?
You COULD plug in your friends PCM and see how it responds (I think you wouldn't even need programming for the engine to run for this check, just connect it and see if it will control the warning light).....is it able to correctly control the battery warning light with the alternator plug being connected and disconnected?

04 blue civic

No other lights. After I disconnected battery earlier car ran for ab a minute then light flashes on and off a few times and stayed on. Very weird. His car needs engine was running fine no lights.

04 blue civic

I did take his alternator just to make sure that wasn't the issue and still light on. Reasoning like you said states and end of diagram to check alternator. Lol

ezone

Again:



Disconnect alternator 4 wire plug again.
Key ON (engine off)

Measure voltage on wht/blu wire in the alt plug....You should see 5v. Do you have 5v on that wire?

Now use a jumper wire to connect wht/blu to ground.... and see if the warning light turned off.

04 blue civic

Problem resolved!!!!!

Picked up an ecm had dealer program and no light!! Thanks for the help all!!

Markus_G

Hi -- I have the same issue with the battery indicator light not going off. 2003 Honda Civic DX 1.7L. (It's been on for 3 years and the car's charging fine -- but I need to sell the car now.)
Regarding the white/blue wire from the 4 pin alternator plug -- when disconnected I measure nearly 0 volts. Your post says I should be getting 5v. Continuity between this wire at the alternator (unplugged) plug and the B10 pin to the ECM is good (and there are no shorts to ground either).

In summary:
Turn engine off. DONE.
Disconnect alternator 4 wire plug again. DONE
Key ON (engine off) DONE
Battery Light is still on? YES
Measure voltage on wht/blu wire in the alt plug....You should see 5v. Do you have 5v on that wire? No.
Have continuity from wht/blu to PCM-B10? YES
No continuity to ground on same wire? (no short to ground) No short to ground.

Might this indicate that the ECM is bad assuming the ECM is supposted to output 5v?

Any suggestions welcome. Thanks.

ezone

Yes IMO it sounds like your ecm has lost that 5v

I'd probably try to grab a good used compatible ecm from a junkyard and plug it in to your car, repeat the tests to prove if thats the root cause or not.

The engine will not run until the replacement ecm is programmed and it recognizes the immobilizer and keys though

Markus_G

Thanks so much ezone. I'll try to figure out something and I'll let you know if I get it to work. Either way at this point it looks like I'm going to have to plop down some money to make further progress. Thanks for your interest.

TypeR_ep3

hi there im buying a type R ep3 with this issue, the guy has replaced both altenator and battery, so I'm guessing it's this 'ECM' you mention. I've searched ep3 ECM and all it's coming up with is the main ECU for the car... is this right? What is this ECM? And rough estimate on price of second hand ECM? So I know how much to haggle on price of the car?
many thanks

BrotatoChip

ECU - Electronic control unit. General term for any control module
ECM - Engine control module. Term used in a car with a manual transmission
PCM - Powertrain control module. Controls both the engine and transmission (auto)