Rep Power: 0

I have a 2009 civic LX coupe that will start fine in the morning and then around two or three in the afternoon in the heat of the day it will not start. The green flashing key will come on at that time and it will not start. When you try to start it will crank but won’t run and you can do it long enough to where you have to jump the battery. If you wait later on in the day when it starts to cool off then it will crank and run. It will strand you in the middle of the day when it’s hot. If it’s an overcast day it will start all day long but if the suns out and the hottest part of the day the green light appears and it will not start. We’ve got four keys and have changed the immobilizer and they have been reprogramed so they match and still the same issue. Any help would be greatly appreciated. Frustrated in Florida!

 
Rep Power: 367

something to do in between the immobilizer and the ECU.
heat also drops electric conductivity of the wires.
What, i have no idea.
Have you taken it to the dealer? They are the best to deal with the green key given they have a good tech

 
Rep Power: 0

Thank you

I’ll try that. I’ve changed the battery cables both ground and hot completely. Can’t figure out what else to do.
I guess I’m taking it to the dealer. 😩

 
Rep Power: 0

I'm no mechanic obviously but check your fuel relay and main relay circuit boards for cracks on the soldered points. Heat will cause them to expand and if they've been there awhile the intermittent heat and cold will crack the contacts. Reflow with a soldering iron. Also check temp control sensor, could be reading cold not hot. Does it crank or does nothing? If nothing check your starter solenoid, if it's copper it could just be hot which is a bad solenoid. You will know if you can jump across the solenoid. I had a Chevy and a Ford truck both do that. The Ford was easy to diagnose, the solenoid was separate from the starter on the firewall but on the honda its right with the starter on the left side of the engine. With the air breather apparatus off its easy to see and access.

 
Rep Power: 222

Green key flashing is immobilizer issues, the computer is preventing it from starting.

 
Rep Power: 0

If it’s below 20F it may cause the immobilizer to malfunction. Warm the key and keyhole area with a blow dryer or a ziplock baggie full of hot water.