P0420 and overheating
 

I got a used '04 8 a month or two ago now it is throwing the CEL with the p0420 code, but it is erratic sometimes the CEL will go off for a day or two but come back on with the same code. No rotten egg smell or any unusual smells.

Also, any time it gets to about 75 degrees or hotter outside the car overheats. I was going to replace the thermostat but was wondering if the cat would have anything to do with it. I've not checked the waterpump yet, but there is no spots from leaks under the car.

Any pointers or help would be most appreciated, thanks!

i think that code is for the gas cap...

does it stay cool as you drive?

Thermostat, cooling fans not coming on..could be the fan. relay, fuse wiring

Belt OK? PCM not turning on fans ( less likely)

Well when I shut off the car I can hear the fans roaring, but could it still faulty even if it does that? I checked the 40a fuse and it is fine. Any way to check the relay/wiring?
Edit: just checked belt too and it is fine.

The 420 is for the cat.

When you say overheating how do you know? Is the gauge on the dash going high? Or are you monitoring coolant temps some other way?

It would be worth it to flush your coolant and put in some fresh stuff since you bought the car used. Who knows what's in there right now....

If the fans are both running it wouldn;t likely be that..the realys control the fans..so if the fans work the relays are OK

If it is indeed overheating....better check your thermostat...

And replace the coolant while you are at it :)

The gauge on the dash is going up high (i have to stop/turn off the car to get it to go back down).
The coolant is fine, but going to replace it anyways when I do the thermostat.

Edit: I am just being picky and all but is there a howto to replace the thermostat on these things. It is normally straight foward but better safe than sorry! (and yes I've changed thermostats on my MX-5s and RX-7s I've had :p)

Bunch of crap to remove out of the way...but not difficult by any means :)

Coolies. Thank you!

Also could be that the thermostat failed or is failing.

I thought the P420 was the 2nd fan relay was faulty.. Dont have the code section with me.

Bleh, changed the thermostat today (that secondary air control valve thingy is a pain!) but ended up flooding the car. Tried pulling the fuse and cranking it for a bit then putting it back on it caught a few times but didn't start. Pulled out the plugs and cleaned them the best i could and took out the fuse again and cranked it to get all the garbage out... then put it all back together with no dice. Put some windshild washer fluid in there and no dice. I must really have bad luck or something :(

Pull start it....tie a rope to the hook in the front...it will start within a block :)

Yeah if I had another vehicle maybe, could maybe try rolling it down the hill and trying to start it but that would be kinda crap if i can't lol

just wondering cause right before i reset my CEL after changing my sparkplugs i got a code (P0420) and it said "Catalyst efficiency below threshold bank 1".

If your cat is blocked, it could cause overheating. That's what happened to me when I WOT 1st to 3rd since I started having high rev issues and slight power loss. Caught the dummy gauge moving towards first warning zone and i backed off, removed midpipe and found the cat collapsed.