I have a 2003 Honda Accord EX 2.4 l they ran and drive perfectly when I left it at my mom's house for storage because I bought a work truck and couldn't drive two cars... After the winter my mom had decided that she was going to buy me a new battery when she went to go start my car and it didn't power up the way that she thought it should and when she got the new battery she hooked it up backwards temporarily but quickly unhooked it within 10 seconds of it being hooked up. Ever since then I've had absolutely no spark whatsoever and any of the spark plugs... I replaced 100 amp fuse/ I replaced the relay for the ignition coils/ I replaced the starter /I replaced the ignition switch/coil packs and spark plugs / and now I have crank but no start no spark.. I'm not really handy with how to use a multimeter for the most part and when I went to test the connectors for the coil packs there was 12 volt on the coil plugs and when I put ground middle hole and red pin left hole I got 12.3V but when I tested the ground middle and red right I got 0V I dont know if that means anything .... I also sprayed starting fluid into the combustion and try to start it and that's when I realized I wasn't getting any spark whatsoever I thought it was a fuel issue but my fuel pump seems to be engaging perfectly fine when I turn it to the on position... I am so lost on how to diagnose this and figure out how to get my Honda to run again I really could use help... My truck is no longer usable the transmission completely went out and it would cost more to get a new one then it would to get a new truck so my Honda is my only hope to hopefully make it work again diagnose what's wrong where I'm losing the power and get it running so I have a vehicle to get to work... I don't know if this matters but when I did the scan tool the crankshaft sensor camshaft sensor we're coming up faulty on the check engine light so I replaced both those and now it comes up with the code p0685 and I have no idea where to start to diagnose the problem with it

 

The reversed battery is obviously bad for the electronics and wiring. The fuses protect downstream electronics against a dead short that happend when the battery was installed backwards. It is posslbe you have multiple blown fuses or a damaged electrical component/wiring. Before installing any new parts on the car, you need to check your fuses. If you still have the original parts, keep them, because Honda parts are typically better quality than the aftermarket stuff you can buy at the parts store.

The quickest way is to use the DC volt setting on your volt meter. Turn your car key to the II position. Touch the volt meter black lead to a good ground. For the engine bay fuse box, use the - battery post. Then use the red volt meter lead to touch the top metal tab on each side of every colored fuse. A good fuse will have 12.? V on each tab. A bad fuse will have 12 V on one tab and no voltage on the other tab. A fuse with no voltage on either tab means you have to figure out why power isn't making it to the fuse.

This is quick and easy to do. Watch a few youtube videos on how to check car fuses in place to see what I'm talking about.

Do this for the engine bay fuse box and the on under the driver's dash. Replace any blown fuses and try to start the car. Recheck the fuses to see if they blew.

Let us know of any fuses that keep blowing or have no power on either tab.

 

I have checked all the fuses and all the relays underneath the dash underneath the hood and all of them have tested out to be okay I replaced the ones that have needed to be replaced and still am not getting any spark whatsoever. the code is p0685 which means there is a circuit open that's losing electricity somewhere between the relay for the coils to the fuse box to the actual coils themselves. I'm not handy with a multimeter nor do I know which settings to put it on in order to test the continuity or the voltage and don't know what to test to tell where the breakage or failure in the electrical is happening.....it's soo frustrating cause I feel so close to having it running again

 

P0685 is an PCM (aka engine computer code), so it isn't a coil code. When you get an error code, the root cause can be a failed sensor, damaged wiring, or how the signal is generated. Looking at the troubleshooting for P0685 doesn't have many tests, so your PCM might be fried. It is possibe you have a missing power supply to the PCM. I do not suggest getting a new PCM just because of the P0685.

Pullling out each fuse tells you that the fuse didn't blow, but the fuse may not get any power. That is why I suggested the volt meter test with the fuses plugged into the fuse box. It is a quick and simple test. You already described measuring for voltage on the coil connector, so I'm suggesting the same meter settings to test the fuses.

 

How do you go about testing the relays ? And on the coils connectors I've tested for voltage ...the very left one had 12v the middle is ground and the right one has 0v ...I will test all fuses again and see what comes of it but didn't know if that bit of knowledge is helpful or not