Cars a 1998 accord v6 ex at, 150k. Light came on and I went over to auto zone to have them read me the codes. first code is P0401 egr, and P0420 bad cat. before I spend money on a cat. If I change the egr valve and clean the port out will that fix my bad cat code or should I replace all 4 O2s too?

 

Well, first the good news, you don't have 4 O2 sensors.

Fixing the P0402 is unlikely to fix P0420, but certainly start w/ cleaning EGR system. It's a pretty extensive job on V6 if memory serves. Check DIY forum and youtube for videos.

Regarding P0420, vigorously shake the converter by hand. Any loose rattling sound is indicatin that converter matrix has failed. If OK, inspect exhaust system for leaks. Repair any leaks.

Next check youtube video by briansmobile1 for use of IR temp gun to check for catalytic converter function.

good luck

 

ow ok I was told I hand for and it would be $700 plus to change them out. I said f.... this and ill do it myself.

Yes it dose I watch a couple of videos on youtube about cleaning the egr. I have to take a part the whole top of the motor.

ok, I looked for leaks already on cold days and I do not see any exhaust leaks at all.

 

I cleaned out the egr port and upper and lower manifold and tb. they where full of build up. the egr was solid. I did not replace the egr valve it self because I went to and one of the bolts where rounded over I ran out of time. I have to try and get it off this weekend.

I reset the ecu and the car runs better and stuff but the ligths back on. So I was going to go and get a up stream and down stream 02s. What brand is the best for the accord. I want a plug and play. Bosch, Denso, NTK?

I also pulled the plug wires just to see how they where and on the front of the motor all the way to the left, it had oil all over it so did the top of the spark plug. the middle plug had a little oil and the driver side one was dry and just looked white. Is this a bad head gaskit going?

 

anybody? this is what they look like.

 

I would suggest to disconnect the battery and clear the codes. Drive the car until the check engine light turns on. Have the codes scanned again. Maybe the EGR code went away and you can not worry about the rounded bolt for now.

Denso makes the O2 sensors for your car. Check out densoaftermarket.com for the O2 sensor. I suggest checking the codes first before replacing the O2 sensor. I would only replace the O2 sensor that is in the catalytic converter (the P0420 may still be a bad catalytic converter). The primary O2 sensor is not giving you a code, so I wouldn't mess with it.

Oil in the spark plug tubes is more common for the 4-cylinder accords. Haven't seen many posts with this problem on a V6. The V6 may have spark plug tube seals for the valve cover like the 4 cylinder and would be pretty straightforward to fix. I would fix this as well before going to the O2 sensor.