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Discussion Starter #1 (Edited)
2007 Honda Civic EX cranks but no start when hot. Possible heat soak related issue. No clear error codes. Will run perfect all day long (after starting cold) but as soon as I turn the engine off, it won't restart until cold. The first instance happened randomly. Car will crank all day long. Relays and fuses all check out fine. ECU doesn't fail under heat. Relays don't fail under heat. I've replaced both the cam sensor and crank sensor. New engine temperature sensor. New starter. New battery. Good alternator. Didn't fix it. My crank no start Symptoms can be replicated by removing the PGM-FI main relay when cold. If I pull said relay while engine is running, engine dies. However the car will run in "heat soak fault" mode without dying until the engine is turned off, at which point it won't restart until cold. I pulled the ECU and reinstalled to rule out a bad connection. Didn't fix it. Engine and frame are well grounded. My basic code reader won't sync to ECU when under heat soak fault situation. Code reader won't sync to ECU when pgm-fi main relay is removed either. Engine temperature display on dashboard goes dark under fault, and also when I remove the PGM-FI relay. No power to fuel pump and no spark when faulting however if the car was running when the fault began, the car continues to run fine. It's almost as if a start-up/power-up sequence isn't being executed (or is being aborted) under fault. No collisions ever. Car has lived in Arizona desert it's whole life (no major salt or water corrosion). Please help!

Tags: 2006 2008 2009 2010 2011 DX 1.8 R18A
 

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Have you checked the key, immobilizer module and ignition system?

Once the engine is switched off and the key is pulled out the immobilizer gets activated. And once key is inserted it should be deactivated. So, if there is a problem in reading the key code the immobilizer won't get deactivated and the car wouldn't start.

If the issue lies here, then replacing the immobilizer module with or without a new key and fob may help to solve it.

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Discussion Starter #3
Have you checked the key, immobilizer module and ignition system?

Once the engine is switched off and the key is pulled out the immobilizer gets activated. And once key is inserted it should be deactivated. So, if there is a problem in reading the key code the immobilizer won't get deactivated and the car wouldn't start.

If the issue lies here, then replacing the immobilizer module with or without a new key and fob may help to solve it.

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Thanks for the response! I'll look into that some more. I am not getting any immobilizer errors when this crank no start fault occurs and the fault goes away after the engine cools down. I've had to order new keys in the past and have them programmed. Before the new keys were programmed, I had them cut and they wouldn't start the car and I'd see a key icon light up indicating that the keyfob chip wasn't a match. Anyways, I've seen immobilizer errors on my civic and it doesn't appear to be the case this time. Although, it could likely still be an error with it. Thanks again.
 

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Thanks for the response! I'll look into that some more. I am not getting any immobilizer errors when this crank no start fault occurs and the fault goes away after the engine cools down. I've had to order new keys in the past and have them programmed. Before the new keys were programmed, I had them cut and they wouldn't start the car and I'd see a key icon light up indicating that the keyfob chip wasn't a match. Anyways, I've seen immobilizer errors on my civic and it doesn't appear to be the case this time. Although, it could likely still be an error with it. Thanks again.
Since you've already replaced most of the components and you also mentioned that your dashboard display also blacks out when hot, there is a remote possibility that this could all boil down to the ECU even though there are no error codes. In some rare cases I've seen electronic boards develop loose connections or loose contact under heat when used continuously. This happens due to hairline cracks in the PCB tracks or at times some faulty resistors or diodes open up due to heat under prolonged use.

So if you could get an ECU from the same year, try replacing it and check when the engine is hot, before buying.

This may not be the fault in your case but try it if you can.

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Discussion Starter #5
Since you've already replaced most of the components and you also mentioned that your dashboard display also blacks out when hot, there is a remote possibility that this could all boil down to the ECU even though there are no error codes. In some rare cases I've seen electronic boards develop loose connections or loose contact under heat when used continuously. This happens due to hairline cracks in the PCB tracks or at times some faulty resistors or diodes open up due to heat under prolonged use.

So if you could get an ECU from the same year, try replacing it and check when the engine is hot, before buying.

This may not be the fault in your case but try it if you can.

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Yes, I've suspected the ECU from the beginning but what I did to test it was get a heat gun and heat up the ECU to maybe 190 degrees Fahrenheit to see if I could cause/isolate the heat related problem. The car engine was cold when I did this and started just fine with a very hot ECU. I also took out relays and heated them up one by one and tried to replicate the fault. No luck there either. I went as far as trying to open the ECU and inspect the solder joints and motherboard but the thing was nearly impossible to open with basic tools since they are effectively glued shut. I didn't want to damage the thing. And my dashboard temperature indicator light will work just fine until I turn off the car when hot and try to restart. I lose power to the ignition (no spark), fuel pump, and temperature indicator light simultaneously when the vehicle is faulting but only after I turn off the engine and turn it back on. I'm at a loss but might try to buy a used ECU off ebay and see if that fixes it. Thanks for your input!
 

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There's a lot of difference in the way the ECU heats up when power flows through it and is in use to artificially heating it up through an external source.

My suggestion would be to check with your friends and contacts if they've a car from the same year and try using the ECU form it for a day, before spending on ebay or any junk yards.

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Discussion Starter #7
There's a lot of difference in the way the ECU heats up when power flows through it and is in use to artificially heating it up through an external source.

My suggestion would be to check with your friends and contacts if they've a car from the same year and try using the ECU form it for a day, before spending on ebay or any junk yards.

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I think you are right on. After your last suggestion, I thought about it some more and it makes sense that when you run power through circuits and resistors it creates a lot of heat internally on the board itself, especially if they are cracked or damaged. Heating the ECU externally wouldn't have the same heat impact on the circuits themselves. What I've done is removed the ECU and I'm having it shipped to a Honda ECU repair shop to have it inspected/repaired ($90-$180, depending on scope). I've got a spare vehicle in the meantime which has been a lifesaver. In a few weeks, I'll reinstall the (hopefully) repaired ECU and see if that fixes the problem. BTW I really appreciate your time on this one. You've helped me a lot and I'm sure this thread will help many others with a similar situation. I'll definitely post a resolution when I nail this down.
 

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I think you are right on. After your last suggestion, I thought about it some more and it makes sense that when you run power through circuits and resistors it creates a lot of heat internally on the board itself, especially if they are cracked or damaged. Heating the ECU externally wouldn't have the same heat impact on the circuits themselves. What I've done is removed the ECU and I'm having it shipped to a Honda ECU repair shop to have it inspected/repaired ($90-$180, depending on scope). I've got a spare vehicle in the meantime which has been a lifesaver. In a few weeks, I'll reinstall the (hopefully) repaired ECU and see if that fixes the problem. BTW I really appreciate your time on this one. You've helped me a lot and I'm sure this thread will help many others with a similar situation. I'll definitely post a resolution when I nail this down.
I was just sharing my thoughts...

Let's hope that the issue is sorted out soon and you get back to enjoying your car.

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Discussion Starter #9 (Edited)
RESOLUTION: I got a call the other day from the ECU repair shop telling me that my ECU was fried beyond repair. They are shipping the core back to me for a $15 fee. The good news for me is that the real problem was discovered. Fortunately, I found a used ECU on ebay for about $100 that was a part number match to my original. I installed the used ECU and had a mobile automotive locksmith come out and program the unit to accept my existing keys which cost me $185 for the service. The Civic works great now. My car still has the same miles on it as it did with the old ECU. I was surprised that I didn't have to take it in to a dealer but the locksmith said beforehand that ECU swaps weren't a problem and that he'd be able to make it work. He was right. Problem solved!
 
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