Engine Light But How To Fix

mattc · January 13, 2010

Right then had a Engine Management light come on on my IS200 on Friday.

So bit the bult and took it to my local Lexus (Wolverhampton, top service) they diagnosed the fault as

P0420 Catalyst System Efficiency Below Threshold (Bank #1)

The guy said it was nothing to worry about and reset the ecu checked the car over and gave me an excellent report.

Just wondered if anyone knows what can cause this and how/if it can be fixed?

also just to add it made no different to the way the engine reaced/drives at all.

Comments welcome.............

mattc · January 14, 2010

Done a bit of digging around.

The code is possibly related to the difference in reading from the pre cat 02 sensor and the post cat 02 sensor.

Now I had a new centre section of the exhaust (bit with the cat in) fitted just before xmas by kwik fit. Do you recon it could be related to this? Might pop it back to quick fit to ensure its not leaking or anything.

BhangraMan · January 14, 2010

Matt,

I had the exact fault come up on my 2003 Corolla (Pre IS250) and the Totyota dealer was happy to clear it but said that it would most likely come back as it showed the cat was 'on it's way out.' (Just for info they gave me a quote for around £1200 to have a new one fitted!!)

After having it cleared I was happily driving away, but then after about 100 miles or so the Engine Management Light returned. So I had it checked to see what the fault was this time and it was indeed the same Cat efficiency fault.

My point is, even though you have had it reset it may still return. I thought of two things when the light came on:

* If the fault is detecting a discrepancy between the pre and post cat sensor, how do they know it isn't the sensors that are faulty as opposed to the catalyst itself (Obviously

they may want to assume worst case so they get the most of you)

* Secondly, my fault apeared quite soon after I had my M.O.T. done. I thought, if the cat was on the way out then the emissions test must have been close to failing. Checked

it and it had passed with flying colours.

After having the light reset a second time I'd sold the car to purchase the IS250 I have now, so I can't say how it's acting now.

Just beacuse the light comes on though, I don't like the fact that they suggest replacing the whole cat straight away, when it's possible it may be a faulty sensor. (I design the equivalent of cat converters for aircraft for a living so I'd like to think I know what I'm talking about!)

Hope that helps mate :)

mattc · January 14, 2010

Well as said the cat was replaced anyway just before xmas as that bit of the exhaust was knackered.

I recon its a faulty sensor on bank one, will do a resistance check on it to see if its functioning correctly. As if it was the cat I would think it would show 2 faults one for bank one and one for bank two.

Am I right is thinking the front 3 cylinders is classed as bank 1?

BhangraMan · January 15, 2010

I would have assumed that was the case but just to be sure, and to make sure I didn't give you false information, I did some digging on the net and found some info to confirm your theory.

This website, LINKY has the following statement:

'...It depends on the model year and type of engine. On most four and straight six cylinder engines, there is usually a single oxygen sensor mounted in the exhaust manifold. On V6, V8 and V10 engines, there are usually two oxygen sensors, one in each exhaust manifold. This allows the computer to monitor the air/fuel mixture from each bank of cylinders.'

So that confirms that the first 3 cylinders would indeed be classed as bank 1.

flyeris · January 16, 2010

I would have assumed that was the case but just to be sure, and to make sure I didn't give you false information, I did some digging on the net and found some info to confirm your theory.
This website, LINKY has the following statement:

'...It depends on the model year and type of engine. On most four and straight six cylinder engines, there is usually a single oxygen sensor mounted in the exhaust manifold. On V6, V8 and V10 engines, there are usually two oxygen sensors, one in each exhaust manifold. This allows the computer to monitor the air/fuel mixture from each bank of cylinders.'

So that confirms that the first 3 cylinders would indeed be classed as bank 1.

I got the same ECU error on my IS. I am thinking of getting an oxygen sensor spacer for the post-cat oxygen sensor into cheating the car that everything is Ok.

http://cgi.ebay.com/ebaymotors/TESTPIPE-FI...=item20add6420c

..or any other... lots to choose from