Hi, I am new to this post. thank you for the support!
I have 2004 honda civic LX 1.7 - history of the car is major overheating problem (on and off for about 2 years) / it was seen by 4 different mechanics and could not find the Issue. finally temp stayed on normal temp - head gasket replaced/ new water pump / new radiator / new hose / new temp sensors./ new thermostat.... after 2 months car looses power doesnt go over 50mph cannot go uphill it takes about 20 seconds to reach 20mph from a full stop. key light is blinking / temp is all the way down to C / check engine light is on / I took it to autozone to test batter and alternator it all passed the test. I plug by OBD2 reader cannot link to my computer. please help thank you!!!

P.S. I saw the belt for alternator is very loose but I already fixed that Issue but still no improvement!

 

Is the check engine light just on or is it flashing? Was an alternator bolt loose causing the belt to come loose? Since you cannot connect to the computer it may be a bad ECU.

 

Check engine light is solid light. alternator bolt was missing I got a replacement bolt and fixed it. I tried connecting over 20 times no luck. and tested my OBD2 on my corolla it works just fine.

 

Yeah since you cannot connect with your OBD2 my guess would be the ECU is fried. The alternator bolt coming loose is a common problem, this effects the grounding of the alternator and ends up frying the ECU. I've read about the same thing happening quite a few times.

Did the bolt work loose before or after you had the HG replaced? The alternator needs to be removed to pull the head off.

Just get a salvaged ECU off eBay, they run around $100, easy to replace. You will need to match your transmission and if you have side air bags or not. You will also need to drive the car to the dealer and swap the ECU in the parking lot, then have them re-program the key so it'll start.

 

Thank you! It might be the ECU. Head gasket was replaced like 8 months ago. alternator bolt missing and belt loose just happen couple days ago. I will get an ECU replacement tomorrow and will let you know next. Only a Honda dealer can re-program my key start with the new ECU? do they charge? how much? thanks again!

 

ok,I brought it to my mechanic to have it double check! He went to the shop where they sell ECU they said if the ECU is toast the car wont start! and thats also my mechanic told me. he said my ecu is fine. he think the problem is the key and the immobilizer. it sends to the computer that I am using a wrong key so the gas wont give 100% when I step on it.
thats why the car is accelerating really slow and wont run over 50mph. we'll see today what my mechanic will say. any adddition? or think whats wrong with my car please help!!!!!!! thank you!

 

Yes if the key light is on you need to take it to a dealer and have the car re-synced to the key chip, or maybe the chip in your key is not working. The anti-theft feature is kicking in and reducing performance.

 

I thought a messed up immobilizer would prevent the car from starting? That's the point isn't it? It's an anti-theft feature, wouldn't do much good if the car would still start.

There are threads out there where a loose alternator bolt fried the ECU yet the car would still run, just pooly (like in limp mode) with weird problems. Here's an example:
2004 Honda civic ex 5 speed. wierd issue...limp mode? - Honda-Tech

and another:http://www.civicforums.com/forums/21...al-issues.html

What really gets me thinking its the ecu is you cannot connect to it. That's a tell tale sign there's something wrong with it. Maybe take it to Honda and see if they can flash it.

 

thank you very much for the link!!! sounds very similar!! let me try this one and il let you know how it work out. now i just need to look if where the ECU is located at the passenger side.

 

ok we can close this thread now! I bought a combo (ECU,immobilizer and the key)
just to make sure immobilizer is not broken too! and to avoid towing my car to the dealership! car works just fine and runs great and back to normal !!!! otherwise just buying the ECU alone should be fine too but i have to tow my car to honda which cost money and re-program the key cost another money.