kens96 Posted November 5, 2007 Report Share Posted November 5, 2007 A quick question. My 96 Eldo threw this code this morning P0420 - Service Emission System came up on the DIC. I looked it up and it say the code is for "Catalyst System Low Efficiency." What should I be looking for if anything. I reset it while driving into work and it has stayed off. Phantom code ? Bad gas? Ken Link to comment Share on other sites More sharing options...
wiz6728 Posted November 5, 2007 Report Share Posted November 5, 2007 I WOULD START WITH CHECK'N THE O2 READING WITH A SCAN TOOL. IF THEY R WORKING LIKE THEY SHOULD I WOULD CHANGE THE CONVERTR Wiz DRIVE IT LIKE YOU own it!!!!!! 1967 chevy II ( FOR SALE!!!!) 1995 Lexus Es 300 1998 SLS Link to comment Share on other sites More sharing options...
apache13 Posted November 5, 2007 Report Share Posted November 5, 2007 A quick question. My 96 Eldo threw this code this morning P0420 - Service Emission System came up on the DIC. I looked it up and it say the code is for "Catalyst System Low Efficiency." What should I be looking for if anything. I reset it while driving into work and it has stayed off. Phantom code ? Bad gas? Ken What about having an emmision's test? If you don't have a scan tool you can just have the car emmissioned if you have a chance. The test will give you a good picture of your overall emmisions and answer the phantom code/bad gas question... Do you stick to the same gas station when you fill up? (I stick to premium from Shell when I fill up my Eldo)? I tend to avoid Mom and Pop gas stations (even if they are a few cents cheaper than Shell) because of the 'bad gas' issue (the mom and pop stations tend to sell alot of reguluar gas as opposed to premium gas so it sits longer). Link to comment Share on other sites More sharing options...
kens96 Posted November 5, 2007 Author Report Share Posted November 5, 2007 Have been filling it with BP since I bought it. I could switch to Shell. That's what I use in the vette because of the fuel guage sending units. I have searched and read some of the posts on this. I have no loss of power and still get about 20 mpg. We don't have emissions testing in Florida. I think I'm going to watch to see if it comes back and see if it goes to history when I restart the car. Link to comment Share on other sites More sharing options...
kev2 Posted November 5, 2007 Report Share Posted November 5, 2007 If vehicle is STOCK.... NO other codes.... Have not added any suppliments... Suggest you clear (?) code ......sometimes a LONG drive getting Cat hot may MAY help. As mentioned The troubleshooting for this code involves conparrision of pre and post 02 sensors readings, often seeing the shiftiing or lack of will show a bad cat BUT will also eleminate the 02 sensors as cause. Link to comment Share on other sites More sharing options...
Cadillac Jim Posted November 5, 2007 Report Share Posted November 5, 2007 Either one of the two oxygen sensors on your Cat, one before and one after, are disconnected or bad -- probalby the rear one -- or the cat is bad. I would start with checking the connectors to the to oxygen sensors. Cats tend to last forever on a closed-loop DFI system like the Northstar unless there is a problem with the gas or an engine problem. Problem gasolines are leaded gas, gas with too much phosphorus (Conoco TCP of yore) or other octane boosters or other gas additives not certified for catalytic converters, too much alcohol for your system (max of 10% according to the manual but 15% shouldn't hurt anything if it absolutely doesn't exceed that ever), or contaminated gasoline. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
kens96 Posted November 6, 2007 Author Report Share Posted November 6, 2007 Drove home without incident. Actually average MPH is hirer than normal maybe because outside air is in the high 60's than in the usual 80's. I will keep an eye on it but want to prepare for replacing the O2 sensors. Car has 142K on it. How many are there and where are they located ? I see in the posts bank 1 and 2, plus 2 on the cat. Is there 4 total? Diagrams pictures appreciated ! Link to comment Share on other sites More sharing options...
Ranger Posted November 6, 2007 Report Share Posted November 6, 2007 '96? One on each manifold. One pre-CAT and one aft-CAT. Link to comment Share on other sites More sharing options...
kens96 Posted November 6, 2007 Author Report Share Posted November 6, 2007 Thanks Ranger ! I guess I'll go with Jim's suggestion and change the pre and post cat sensors first since I have not had any codes suggesting the manifold ones are the issue. We will keep you posted. Link to comment Share on other sites More sharing options...
Ranger Posted November 6, 2007 Report Share Posted November 6, 2007 But you don't even have a DTC for a bad O2 sensor. Sounds to me like the DTC is pointing at the CAT, no? Link to comment Share on other sites More sharing options...
Cadillac Jim Posted November 6, 2007 Report Share Posted November 6, 2007 A bad heater or sensor on the pre-cat or post-cat sensor will cause a bad cat code. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted November 6, 2007 Report Share Posted November 6, 2007 But if the sensor was bad it should also set a sensor DTC I would think. Link to comment Share on other sites More sharing options...
kens96 Posted November 6, 2007 Author Report Share Posted November 6, 2007 Car is running great. No performance or acceleration issues at all. Wouldn't a bad cat give me poor performance or a rotten egg smell ? Link to comment Share on other sites More sharing options...
Ranger Posted November 6, 2007 Report Share Posted November 6, 2007 Only if the CAT is plugged will it affect performance. Link to comment Share on other sites More sharing options...
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