2002 Civic EX
To make a long story short, my immobilizer/green key light stopped coming on when I turned my key on, so I was getting crank but no start, after I checked every fuse and wire and cleaned and checked all my ground wires and doing tons of reading and research with no luck, I bought another transponder (the ring with green plug in the steering column that actually reads the chip in the key) once I got the new one and installed it my green light started coming on once again and would continue to blink, which I knew was supposed to happen so I figured at this point my old one was faulty and now I just needed to reprogram my keys to match my new one, yesterday the locksmith came by and has the best equipment Ive ever seen and it was saying my 2 keys were now stored to the car, the computer was communicating with my car, everything looks like it should, but as hes packing up thinking hes done, the green light is still blinking. He does everything again, same thing, he clears all the keys and even cut me a brand new virgin key and tries it and my 2 original keys one at a time, still blinking green key light. We even put my old transponder back in, no green light , no nothing, it wouldnt communicate with that one, put the new one back in, tried it all again, nothing, still flashing green key light. Any suggestions would be greatly appreciated, the only component that was changed was the transponder in the steering column, theres no after market alarm on the car no extra wiring at all to anything. Thanks in advance for any help or advice.

 

1. To clarify the definitions to avoid confusion in relation to your original post and the following information I will post.

• The 'transponder' is embedded in the ignition key.
• The unit at the steering column you replaced is the 'immobilizer control unit-receiver.'

2. There could be different causes for what you're experiencing. Some of which may be caused by the following (but, not limited to):

• Short or open (break) from the ECM/PCM to the immobilizer unit
• Low car battery voltage (check car battery and make sure battery connections are clean and tight)
• Interference by noise with communication between immobilizer unit and ECM/PCM (some aftermarket device, etc.; causing noise interference)
• ECM/PCM failure

3. Some things to check:

• Car battery and connections as previously indicated.
• Is there a Honda CarLink Interface Module installed (located behind the middle of the console) or some other aftermarket accessory plugged in nearby? These may cause interference noise.
• Disconnect the 7P connector at the immobilizer unit (steering column) and Connector E at the ECM/PCM (located behind glove box). Check for continuity between Immobilizer Unit side connector terminal no. 1 (Brn/Yel wire) and the ECM/PCM Connector E terminal no. 3 (Brn/Yel wire). Also check for continuity between Immobilizer Unit side connector terminal no. 2 (Red/Blu wire) and the ECM/PCM Connector E terminal no. 27 (Red/Blu wire).

Brn/Yel is a brown colored wire with a yellow stripe running through it. Red/Blu is a red colored wire with blue stripe. No continuity would indicate an open (break) in the wire or connectors that go between the immobilizer unit and ECM/PCM.

 

Thank you very much, the locksmith is supposed to come back on monday after he did some research himself, it was such a bummer my car has been down for almost 5 months now and I thought yesterday was finally gonna be the day, Ive had some new parts and hadnt installed them yet because I was waiting til it was back on the road again, so I even installed my new brakes and rotors while I was waiting, got my hopes up and then bam! Denied..anyway Im gonna check for continuity on those 2 wires and try to get a new battery also because mine was weak for sure but the locksmiths fancy OBD computer was showing my cars voltage output on the top corner of his screen and it was low at first (10 volts or so) so I connected a battery charger up to my car and then his computer was showing 12+ volts the rest of time and once he was done cycling the keys and made me a new one also, it showed all 3 keys were programmed and stored, the green key light was doing long slow flashes and rapid flashes while his computer was communicating with my system, but as soon as it indicated everything was done and I went to start my car the green light aid come on, go off for about a second or two, then return back to flashing.. anyway ill check those and try to come up with some money to get a new battery. Ill continue to post the progress on my never ending civic saga... Oh and what if I took a good battery from a different car, the one in our ford focus is slightly larger than the little battery in the civic (its the small kind that is slightly larger than a lawn mower or power wheels lol) but would the bigger battery have any ill effects on it if I just hook it up to the civic while the locksmith does the key programming?? Thanks again

 

I know this sounds stupid but maybe your locksmith was trying to program the ECM instead of the receiver unit?

http://www.hondalac.com/service/Bulletins/x01-053e.pdf

 

Im not 100% sure, he definitely seemed to know what he was doing and I saw on the computer screen it was showing "communicating with immobilizer" and i saw it read 3 keys stored

 

Im still stuck, checked the brn/yellow wires and red/blue wires for continuity they were good so Im hoping the battery is the problem, I read a post from 2014 on civic forum and a guy was talking about the locksmith he called warning him that he would still charge him for coming to him even if it doesnt work because it could be a bad ecm, and the guy mentioned his green light was off and the replacement immobilizer control unit from the junkyard made the light start working again so it couldnt be the ECM, I dont know how accurate that is but hopefully he was right, the reprogramming worked for him, but anyway I would still like to know if I use a regular size battery (bigger than the tiny one in my car) just to hook up for the programming process if that would have any ill effect

 

Ok I'm happy to report that my civic is alive and well! After the professional lock smith came and had no luck, a friend of mine was finally able to borrow a high dollar obd computer from his work and bring it by for us to try. It looked very similar to the one the locksmith had but this time I sat in a watched everything because he told me he wasn't very familiar with the computer so after we hooked a fully charged battery to my car (I don't think the battery was the problem when the locksmith was here) we were getting the same result when trying to add keys but this obd computer was giving us suggestions as to what might be wrong, and they were similar to what was suggested above (another device causing noise or interference, a break in the wires, a low battery) but it also gave a suggestion that said something about the immobilizer control unit not being original or something, I wish I would have documented better, but it said something about programming the ecu) So, on the first menu after selecting 'Immobilizer' from the main menu, there was a few options, add a key, all keys lost, and one that said something like reprogram ECU, and there may have been more, I dont know if the locksmith's had this option or not but my friend's did. After a few attempts of trying to just add keys and the green light continuing to blink, we tried the reprogram ECU option, it asked for the VIN number, it communicated for a few seconds, and after that we added the keys again and bingo, the car fires right up. I don't know if the locksmith had that option or not, I would think if it did then he would have tried it, even though at first it looked like something I would want to avoid, after one of the trouble shooting suggestions mentioned it I was willing to try and it worked. So I guess even though I have read other accounts of immobilizer problems where people changed out their immobilizer control unit and added keys and off they go, mine required the immobilizer control unit to be matched to my ecu, then the keys added to the immobilizer control unit before it worked. I hope if anybody else has this problem they don't have to go through all the crap that I did and maybe my struggle can help them. Thanks to everyone for the help and tips.

 

Do you know the name or brand scanner y’all used