Elgrand E52 CATs - To decore or not to decore

For anyone starting to look at a Nissan Elgrand one of the first things that you will find is a million discussions about cats and whether to have them decored.  Not sure about you, but it was quite confusing when I first began my search.  If it helps, lets start with a quick recap:

On the older model E51 Elgrands, their exhaust system has four catalytic converters, lined up in 2 pairs. There are two front cats and two rear cats, prior to the muffler and exhaust pipe at the rear of the car. It seems that there is a chance that due to ECU errors and excess fuel getting injected, that some unburnt fuel in the front cat can cause it to break down.  When it breaks down it can cause debris which will move from the front cat to the rear cat.  There is then a possibility that the debris in the rear cat could block the cat/pipework.  This in turn will mean the engine cannot expel the exhaust fumes, and some complicated process can then cause the engine to self destruct.  There are quite a number of people who have had the problem and the repair bill is very high as they often need a replacement engine. (There was also a recall by Nissan on the E51's to fix the issue by updating the ECU, but its not clear if that fixed all of the issues.) 

It was very difficult to find out accurate details about the E52 cat system, with people assuming it must be the same as the E51, or just speculating.  The lovely chap who undersealed my car (a must for anyone with an E52 in the UK) took a look while he was there to discover the truth.  The E52 has a three cat system, with 2 front cats and only 1 rear cat (I assume this is the case for all E52s..).  There is no evidence of any ECU bugs for fuel injection, and there is also no real evidence (at this time) of engine failures due to cat failures.  (See the pics below that show the three cat system)

The big question is do you decore the rear cat just to be safe?  Apparently the rear cat is there for initial startup emissions as they are strict about this in Japan.  In the UK we do not have this test for the initial starting of the car, so the decoring of the cats should not cause a MOT emissions failure.  However, it is unclear if it is legal to tamper with them or not, and I believe if a MOT tester finds evidence of a cat being altered then they can still fail the car (could be a myth!).

Fellow E52 owners out there might disagree, but I went ahead and had mine decored.  For me it was a low cost to get it done while being undersealed, and as it isn't going to cause me any issues for MOT tests I decided to play it safe.

With that in mind, I wish you luck pondering the question "To decore or not to decore".

3 cat system on Nissan Elgrand E52


Rear cat on Nissan Elgrand E52



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