joshua.mills

TLDR - alternator mount bolts break>car stalls from dead battery>fixed alt bolts and remounted>car enters limp mode w/ key light flashing>replaced ecu> new one programs, but still will not start the car, key light cont. flashes> now old one wont start the car either> any suggestions? I know you guys have solved similar issues before but this seems pretty specific in my sit.

I am a newbie here with the electrical problems in hondas, so I'm here for some expert advice on what hopefully is a common enough problem this forum has dealt with. Well here's my situation.

I have a 2005 honda civic hx auto, and recently the alternator mount bolt stripped and shook out of its mount. It kept falling out when I remounted it it would keep falling out. leaving it out made the alternator shake around annoyingly. Because I ignored it, the bottom bolt sheared off and the car stalled on the road because the battery died. When I got it home I remounted the alternator and tried to jumpstart it. The car started but it entered what seemed like limp mode, where a glovebox relay would click and engine light would flash in sync with the clicking, and the rev and temp gauges would also jump as well. Eventually it stopped after 10 clicks and the engine light comes on, the two gauges died, and my car didnt sound right at all, like it was running rich. the key light was also flashing i believe. It would not rev past 2500, and wouldnt move without reving it up to that point.

I got a used ecu from the exact same model car as mine and had the keys synced up with used ecu and now the car will turn over but will not start. the key light continues to flash. The locksmith showed that my car was indeed learning and storing the keys. Im guessing i caused some sort of issue changing the ecu without disconnecting ground, and since the alternator failed i could have done more than just fry the ecu but why exactly is this still happening? the old ecu wont even start the car now with both keys programmed to it as well, when before i changed it would start it but enter limp mode. The CEL also blinks around five times then goes away at this point.

Any advice would be great because I would like to solve this and get back in my civic! Thanks everyone

ezone

You mean disconnecting the battery?
I kinda doubt that's the issue, but I suppose anything is possible.
The typical failure is limited to the PCM, from what I've seen.
How weak is the battery? Check all the fuses? Might be time to dig into troubleshooting.

Has the alternator problem been corrected? You don't want to burn up another PCM...
You mean like after leaving the key turned on for about 20 seconds it does this? That's normal until all the OBD monitors have run and passed.

joshua.mills

Thank you ezone, this problem is throwing me for a loop! I tested the alternator when the car was in Limp mode and i determined that it seem to function normally, putting out 14.5 volts, even under electrical load. The alternator just shook loose and broke off its mounts, so I fixed it with a bolt that passes through the whole top mount bracket w/ a nut at the end so it couldnt shake loose again, and a new bolt at the bottom where it had sheared. I made sure it worked and was charging the battery at this point.

After solving this problem and discovering the limp mode issue, i didnt go any further than switching the computers and having a locksmith program the new(used) computer, only to find that after each successful program, the key light still comes on everytime i tried to start the car and would only turn it over, but not start.

At the current moment, i have checked all the under dash fuses, under-hood fuses, and all are good. The current battery voltage is 11.5, so im gonna see if chrging up quite a bit will help. Possibly driving for around 30 min on just battery power when i failed to realize the alternator was not operating could have shot the battery. I feel troubleshooting is all ive got at this point. Thank you for your input.

ezone

Yeah, low battery voltage can cause the immobi to not read or communicate correctly, along with many other possible computer issues.
Charge it up and see what happens.

If no joy.....Without actually being able to test anything or plug in my scanner to see what everyone is thinking..... I might guess at trying another immobi control unit....but then you would have to do the programming all over again so it recognizes the keys and the PCM also can recognize the new immobi CU.



I'd get out a wiring diagram and commence with some circuit testing first though.



^Immobi CU.^