: Help! Service Emissions Soon and Check Engine



johnyhuh
01-31-04, 05:34 PM
96 STS 188k
Is it time to sell this thing? One thing after another!! Last week I replaced a leaky fuel rail and with help from this forum, its worked great (for a couple days.)

I live in Minneapolis and this week we reached -20 degrees fahrenheit. I am now getting a Service Emission Soon on the DIC and a Service Engine soon light. I ran the codes and they say pc0174 and pc0420. I am confused on what I need to replace to get these taken care of. Could this be a result of the cold?

Anthony Cipriano
01-31-04, 09:43 PM
96 STS 188k
Is it time to sell this thing? One thing after another!! Last week I replaced a leaky fuel rail and with help from this forum, its worked great (for a couple days.)

I live in Minneapolis and this week we reached -20 degrees fahrenheit. I am now getting a Service Emission Soon on the DIC and a Service Engine soon light. I ran the codes and they say pc0174 and pc0420. I am confused on what I need to replace to get these taken care of. Could this be a result of the cold?

PC0174: Left fuel trim lean
PC0420: Catalyst system efficiency low

Could be an oxygen sensor starting to get weak and/or maybe an injector getting some ice in it or something like that due to the cold. I would put some isopropal gas line antifreeze in the fuel for the next fuel tank fulls to see if there is any moisture in the system that is causing a problem - possibly this will help it recover.

With 188,000 miles on the car it sounds like it has been pretty reliable. Those are pretty minor things for 188k. Not something to get too upset over. Of course, with 188k on anything it may be time to sell and get something newer.

johnyhuh
03-01-04, 11:15 AM
Here is the latest...

It's been a couple months since the last post on this but I am still running into this problem! After the last post I did pour a bottle of HEAT (iso propal) in my fuel tank. The car ran fine with no codes for about a week and a half. Then the code PC0420 came up along with the Service Emmision System message on the DIC. The temp in Minneapolis went back to the normal 20-30 degrees fahrenheit and I have gone through a couple of tanks of gas since. So the temp and moisture in the fuel is ruled out. I reset the codes and ran the car again. The car ran fine for another 2 weeks then the same codes and lights came on again. I did another reset and the car ran fine for 2 half weeks and then the codes and light came on again.

I finally have noticed that on every occasion that the codes and lights came on, there was a high amount of moisture in the air. Is this an indication that I need to replace all 4 O2 sensors? Or, is it time to replace the catalytic converter?

The car has 118k miles on it (correceted from the first post.) Even when the codes and Check Engine lights are on the car runs fine.

Another factor that may come in to play here is prior to this, I did replace a leaky fuel rail and accedently hooked up the injectors in reverse order causing the car to run in limp mode. I did drive the car in limp mode for a few miles just to get back home. I fixed my screw up and rewired the injectors. The car ran great up untill I first got the P420 code a week after this. Could this have damaged the catalytic or O2 sensors? :bonkers: :bonkers: :crying:

Anthony Cipriano
03-01-04, 03:05 PM
Here is the latest...

It's been a couple months since the last post on this but I am still running into this problem! After the last post I did pour a bottle of HEAT (iso propal) in my fuel tank. The car ran fine with no codes for about a week and a half. Then the code PC0420 came up along with the Service Emmision System message on the DIC. The temp in Minneapolis went back to the normal 20-30 degrees fahrenheit and I have gone through a couple of tanks of gas since. So the temp and moisture in the fuel is ruled out. I reset the codes and ran the car again. The car ran fine for another 2 weeks then the same codes and lights came on again. I did another reset and the car ran fine for 2 half weeks and then the codes and light came on again.

I finally have noticed that on every occasion that the codes and lights came on, there was a high amount of moisture in the air. Is this an indication that I need to replace all 4 O2 sensors? Or, is it time to replace the catalytic converter?

The car has 118k miles on it (correceted from the first post.) Even when the codes and Check Engine lights are on the car runs fine.

Another factor that may come in to play here is prior to this, I did replace a leaky fuel rail and accedently hooked up the injectors in reverse order causing the car to run in limp mode. I did drive the car in limp mode for a few miles just to get back home. I fixed my screw up and rewired the injectors. The car ran great up untill I first got the P420 code a week after this. Could this have damaged the catalytic or O2 sensors? :bonkers: :bonkers: :crying:


It might have overheated the catalyst. If the injectors were miswired and firing at the wrong time it would put a lot of raw fuel through the engine and directly into the cat. Not something it likes as raw fuel will cause it to get very hot and potentially damage it.

There's really nothing to worry about with the "cat low efficiency" code. Just the nuisance to you of the SES light. It really won't affect the operation of the engine/car and isn't something that idicates a potential breakdown or walkhome.

It's possible that the oxygen sensors before and after the cat are getting weak and/or were damaged by the injector wire swapping. I would probably replace the rear one (after the cat) first to see if the problem goes away.

Have you driven the car on the highway to get it good and hot or is it mostly in the city driving in the cold? If it's been short tripped a lot take it out on the highway to clean it out (see the thread about "pushing the button on the Northstar") and build some heat in the cat to clean it out good. The cat needs to be hot to operate but it can be overheated with too much raw fuel dumping into it.

johnyhuh
03-01-04, 06:17 PM
I have run the car hard to get things cleaned out. I also have cleaned the EGR. The car runs fine except for the light comming on occasionally. I do find it interesting that everytime that I reset the vehicle the codes and the SES light takes longer to come on. Could it be that it takes time to clean out the cataylitic? Does the fact that I get the SES light when there is moisture in the air have anything to do with it? I'll reset the computer and try changing the rear O2 sensor. Are there two of them?

Anthony Cipriano
03-01-04, 09:27 PM
I have run the car hard to get things cleaned out. I also have cleaned the EGR. The car runs fine except for the light comming on occasionally. I do find it interesting that everytime that I reset the vehicle the codes and the SES light takes longer to come on. Could it be that it takes time to clean out the cataylitic? Does the fact that I get the SES light when there is moisture in the air have anything to do with it? I'll reset the computer and try changing the rear O2 sensor. Are there two of them?
There should be an oxygen sensor before and after the cat. Combustion-wise there shouldn't be any correlation to the SES and the humidity but possibly there is an issue with the connectors or insulation on one of the O2 sensors. You might check under the car carefully before you start replacing anything. If it is taking awhile before the code sets I would keep driving it and see if the problem goes away. There is a chance that the cat was damaged by some sort of contaminant and that it is slowly being carried away by the exhaust flow.

How was the fuel rail fixed? Did you use any sort of silicon sealer or RTV or anything like that on the rail? If so, the silicone may have poisoned the cat and it is taking awhile to recover.

johnyhuh
03-02-04, 02:29 PM
I replaced the entire fuel rail system. I did not use any RTV of silicon. I replace the O rings on the injectors. Everything was pressure fit. I'll reset the codes again and hope that it goes away. I don't feel like buying a bunch of O2 sensors yet.


There should be an oxygen sensor before and after the cat. Combustion-wise there shouldn't be any correlation to the SES and the humidity but possibly there is an issue with the connectors or insulation on one of the O2 sensors. You might check under the car carefully before you start replacing anything. If it is taking awhile before the code sets I would keep driving it and see if the problem goes away. There is a chance that the cat was damaged by some sort of contaminant and that it is slowly being carried away by the exhaust flow.

How was the fuel rail fixed? Did you use any sort of silicon sealer or RTV or anything like that on the rail? If so, the silicone may have poisoned the cat and it is taking awhile to recover.