Hi everyone,

I recently was able to see what the check engine light was saying with a friends scanner and I got the following codes:

P0700 - Transm. Control Syst. malfunction
P0420 - Catalyst Efficiency Below Threshold

The car has 97k on it, and I think the P0700 code was set after driving in a big rainstorm. I wonder if the downstream O2 sensor is failing causing the other code. Has anyone replaced there catalyst? What mileage?

Thanks, Rick

The P0420/ECM-5A code indicates a Three Way Catalytic Convertor Efficiency issue and may result in poor performance. Possible sources are uneven compression, air leakage in the intake system, leakage in the exhaust system, fauly fuel pressure and defectve converter. Check all of the hoses in the engine compartment first. There are special tools required to fully check for the air leakage issue.

The P0700/ECM-76 code indicates that there are one or more codes stored in the transmission control module. These must be read and erased before you can erase the P0700 error.

This suggests 50k to 100k miles replacement interval for cat.:
http://home.flash.net/~lorint/lorin/fuel/cat.htm
Top Gear is a great British TV series:
http://searchwarp.com/swa32557.htm

Correction: The link refers to a company called Top Gear, not the BBC TV program called Top Gear. So yes, some of the comments are questionable. But most is correct, like don't drive through water, etc. The BBC TV program is great and rated as one of the top car programs worldwide.

More than likely just a faulty cat and unless it is falling apart and clogging the exhaust you should not have any performance issues. You need to do all of the usual checks and make sure that there are no vacuum or exhaust leaks and then monitor the rear 02 sensor. The front one should fluctuate nicely and the rear one should hold fairly even at about .4-.5 volts. When the rear sensor consitantly bounces around like the front one it tells you that the rear sensor is reading the same thing that the front one is and that means that the cat is not doing it's job, in other words the exhaust content does not change when going through the cat. I had one of these in the shop the other day and had the opportunity to monitor it on Vadis for a day before the repair and a day after it and really get a feel for what a good signal looks like in real world application, not just sitting in your stall, as well as what a bad signal looks like. I drove the car to and from home both days. It ended up being the cat just as I figured, replacement cat was about 730.00 list price for the part alone and it should pay in the area of 2.0-2.5 hours to diagnose and replace the part. Make sure that your cat is not under emissions warranty, it may very well be depending upon your mileage

Mark