Car doesn't start on warm days

If the check engine light does not test when the key is turned to on, this is a good pointer to the main relay being the issue. Obviously, in your case, this would be when the car is warmed up or on a hot day. If you pull the main relay, under the driver side kick panel, it can usually be repaired. I had to do this on two cars, 6th gen 4 cylinders (One LEV and one ULEV) so far and plan on doing it to mine as preventative maintenance. It's funny. I was talking to another buddy of mine on the forum here about doing this yesterday. I can post a procedure with pictures later today if you would like. You will need a common screwdriver and a soldering iron. Soldering iron is $15 at radioshack.

What causes the issues with the main relay is that after a number of years, the solder joints become cold on the pcb but can be reflown quickly with a soldering iron.

I see you replaced the relay but this may not be a bad idea to try with your old relay.

Yup. Key switches relay, relay powers ecu, ecu grounds mil.

Resolder that relay, easy. Did some 4g civics. 10mm, flathead, soldering iron (no solder needed!)

Or replace it.

Yup! In any case, I'll do mine later today and write it up!

While I know you already replaced the relay, I hope this helps...

Obviously to protect myself...

NOT RESPONSIBLE FOR DAMAGE DONE TO YOUR CAR FROM THIS DIY. *SHOULD YOU DECIDE TO DISCONNECT THE BATTERY BEFORE PERFORMING THIS PROCEDURE, YOU WILL NEED RADIO CODE*

So first, lets locate the main relay.



Disconnect it.



You will now have to remove the 10 mm bolt on the main relay bracket and slide the other wire harness off its clip to remove the relay with the brace as previously mentioned by xci.ed6. The harness is connected to the relay in this photo because I took this photo after re-installing the relay. I did disconnect the brake pedal switch to make the bolt easier to see.







Remove relay from housing. I used my knife to pry it open on each side and then slide it out.





Warm up your soldering iron and then reflow each solder joint on the back of the board. Make sure each joint melts fully for the most optimal reflow. I believe there are 26 total.





Put relay back into housing and reinstall in car. Make sure you don't forget to slide the gray harness back into its clip and reconnect the brake light/cruise control switch if you disconnected it to perform this procedure.





Let me know how this works out for you if you decide to go this route!

Replace the main relay, keep the windows down an inch or so to let the heat escape on hot days, that's what I always did during the summer issue never came back after that.. also used a window sun shield thingy I found lying around. That's the poor college student way to fix it

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james'99 said:

Yup! In any case, I'll do mine later today and write it up!

Click to expand...

Thanks for the right up man! But even though my main relay was new (twice) it can still be it? I'm thinking about doing that to my oem one and trying it out.


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bairdandrew77 said:

Replace the main relay, keep the windows down an inch or so to let the heat escape on hot days, that's what I always did during the summer issue never came back after that.. also used a window sun shield thingy I found lying around. That's the poor college student way to fix it

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Click to expand...

Haha that's exactly what I've been doing. On Friday I had to get to work and it decided to not start so I pressed on the gas and left it on about 3-4000 rpm and at first it didn't sound very good but it stayed on.


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Yeah, definitely! If the case is that the CEL doesn't test when you turn the key on and the engine is off, I would definitely say the main relay needs to be checked out. Where did your two other main relays come from?

On a side note, you guys are lucky. Expecting snow here in NY tonight...

james'99 said:

On a side note, you guys are lucky. Expecting snow here in NY tonight...

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I left the windows up at night and when it wasn't hot or when the weather looked bad. You guys are still getting snow in NY? That's sucks, it's been surprisingly nice in utah!

Alright, back on topic now

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This sounds like a similar problem my mom had on her 2004 Odyssey. It would start on really hot days then the engine would die and we would try to start it a couple of times and it either would or wouldn't. I think all it was was a faulty ignition with the key and they needed a new one. I could be wrong though.

EDIT: Never mind it looks like you got it.