TTD2013

My engine light went off, and I found out that I had a miss fire engine about a month ago. I just got new head gasket replace couple days ago. Now my engine light went off again with code "P0420 - ... below threshold band 1". Does anyone know why and how to fix this problem? Replacing the head gasket would not cause this problem, is it?

DeathCougar

iTrader: (23)

Read up here: http://www.obd-codes.com/p0420

Couple of likely issues.

#1, Bad Oxygen sensor. This is going to the most likely and certainly the cheapest option. If you replace it, GET DENSO. Do not get the "cheapest" you can get. Bosch and other related Ebay junk will fail post haste.

#2, Bad Catalytic converter. Hopefully your failed head gasket did not cause issues in your Catalytic converter. Usually they are ok, and just the sensor is damaged.

Certainly replacing the head gasket would not cause the problem, however the head gasket failing could have caused a problem that is just now showing itself.

TTD2013

Thank you for the info. How do I know which Oxygen sensor need to replace? There are four of them around the CAT, right?

DeathCougar

iTrader: (23)

Bank 1 is Driver, IIRC. The forward "O2 sensor" is an Air/Fuel ratio sensor I believe. The one aft the cat is the actual Oxygen Sensor. I would start with an FSM and follow the testing procedures, no sense throwing expensive parts at a problem.

j2the-e

Depends on what engine you have. Bank 1 is passenger side on the GR series(v6) and it is the drivers side on the UZ series(v8) engines.

j2the-e

Unfortunately, with an A/F ratio sensor, there is no real way to test the cat without the ability to manually adjust a/f ratio using a scanner. Odds are good, if you have a p0420, you need a new cat.

streetfacts

I have a 2004 Toyota 4 Runner (120k Miles), that has been running perfect until I took it in to replace a window electric controls switch on drivers side and out of their recommendation we changed the fan belt in Engine. Since that day our 4 Runner has not runned well again and I am certain it all had to do with the engine belt replacement or not and was just a coincidence.

After two weeks at the dealer and the same rookie steps, spark Plugs, injectors, ignition coil, water in tank theories and the latest a a head gasket etc, the car is still in the same position where it started.

The diagnostic is that the Cylinder Head is shot… So a mechanic I found in Angies List, which has the greate’s of ratings asked $5,000 dollars to replace the Cyl Head. I find this quite high, when the actual Cyl. Head is $400.00 cost,

Also, its sounds almost better to change the engine to a completely rebuilt engine with warranty.

Anyways, I am have been showing the following engine code: P0306. It starts a rough idle at start up, especially when cold (in mornings) and then it stops and goes back to smooth as usual.

I would like to know if any of the members have had similar experience with this situations.

Thank you in advance for any replies.