My 2005 Subaru Forester is showing a P0420 code with blinking green cruise light and solid orange check engine light sometimes on start up or will be off on start up and will randomly come on when driving down the road. Scanned it with a THINKOBD 100 OBD2 scanner. 1st - Replaced gas cap and erased code. 2nd - cleaned CAT with a CAT cleaner from Advanced Auto Parts and erased code. 3rd- cleaned mass airflow sensor and throttle with mass airflow sensor cleaner and erased code. No luck. Trying to do easy inexpensive fixes first or just leave it alone.
Any help would be appreciated.
Thanks.
How much oil usage? Any coolant loss?
Around a quart every 1k miles. I change it every 5k miles. Coolant is fine no leaking.
@LiamH
Typical and not bad for that boxer but you have a cat going bad. A new downstream O2 may help. You can get a bung to space the sensor a little out of the exhaust stream and may resolve the code being thrown. Tricky tho because of flow dynamics. Also find/fix all intake air leaks (smoke test) and get your ltft to zero (+-4 realistic). Here's how it works so the above will make more sense... upstream O2 measures O2 in exhaust for feedback to computer to adjust for proper a/f ratio (hence importance of knowing all intake metered air (no leaks adding air)). Now the EPA software programed into the ecm intentionally makes it rich from time to time, the downstream O2 picks up this change and utilizes a lookup value in the ecm to determine how long the cat takes to burn off the excess fuel. If it takes too long, throws the code. Coder is simply there and implemented to check the cat... funny thing is... this degrades it (albeit minimally). So moving the downstream O2 a little out of the exhaust stream can change this value/time (usually to your benefit). Hope this helps and keep us posted.
@hillbilly Okay I'm going to use some spark plug non foulers to space the 02 sensor out. Do I need to disconnect the battery to work on the 02 sensor? I've seen people disconnect the battery to replace 02 sensors but I'm just using the original.
Fixed it. Thanks.
Hi. I just bought these o2 sensor spacers from Amazon. It came with 2, so I put both on my oxygen sensors on my 03 Honda CRV. Should I only install one on the downstream sensor and leave the upstream sensor as it is to clear code P0420?
From what I know that worked for me is you install the spacer on the downstream 02 sensor (the one towards the end of the car where the muffler is) and I put just a little steel wool in the spacer just enough so you can still see through the spacer and then install it. Clear the code and you should be good.