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need help figuring out what the problem is 2000 Deville

10013 Views 29 Replies 3 Participants Last post by  Ranger
My Deville just recently went over 100,000 miles and now the "service engine soon" light comes on. Not only that, but the car started like stalling anytime I accelerate from a complete stop. Then the "service engine light" starts blinking. ( Keep in mind I'm not mashing it). I took it to the shop and got the following codes:
Po141-o2 sensor bank 1
Po154-o2 sensor bank 2
po155-heated o2 sensor bank 2
po3000-random misfire
po507-Idle speed high

I got the spark plug replaced, but I didn't get the car scanned again yet. Do the o2 sensors need to be replaced? Or is something causing them to get a bad reading? Where are the fuses for the o2 sensors located? Is all of this related?
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Sounds like you may have CCCCC (Classic case of constipated catalytic converter). A bad cat won't exhaust sufficiently and becomes more obvious at higher throttle settings, ie may idle ok but may load up when you give it gas. I know the PCM compares the downstream O2 sensor to the up streams but don't know what code it would throw. Have you used any kind of solvent around the throttle body? If it contained silicone it will ruin your O2 sensors. You may also need to clean your throttle body using O2 sensor safe throttle body cleaner.

These are thoughts I would have but you may want to post more complete descriptions on the DTCs (codes), hopefully Ranger or Sub will respond, they have forgotten more than I will ever know.
No, cat can't damage the sensors that I am aware of but the computer compares the up stream O2 sensors to the down stream sensor to determine the efficiency (whether it is producing too much back pressure) of the cat. The one thing that will surely kill an O2 sensor is the use of non sensor safe chemicals that can get into the exhaust system. That being said, did they out the chemical in before or after you started getting the O2 sensor codes? If after it was not the problem and if it was a dealer I doubt they would introduce an inappropriate chemical cleaner. Two of the codes ihdicate a problem with the heater portion of the sensors. The heaters are there for cold start up to decrease emissions until it warms up. As I understand it the sensors don't need to be heated once the exhaust has heated them. Do you have a factory (not Clymer or Haynes) service manual? You can subscribe on line to Alldata for an online searchable version or get a set from Helms or ebay. They have trouble shooting procedures for the DTCs, right now I don't have time but maybe later I can see what it suggests in my 00 Deville manuals. It sounds like the heateer circuits are compromised but I doubt both sensors and/or both cables are bad. I would look at the fuses under the hood (passenger side fender well in front of the coolant surge tank and see if there are any fuses or relays associated with the sensors there. I will be working on my car this evening and I will check as well.

I also was thinking about this a little more and it seems that if the heater circuits are the real problem, then once the car warms up if you clear the codes through the DIC the car may run fine until you shut it off again and let it cool off. The instructions for getting the codes and clearing them sould be in a sticky post at the top of this forum page.

I sent a private message to Submariner409 asking him to look at your thread, he is the most knowlegable person I know of on Cadillacs in general and is well versed in things automotive in general.

Keep us posted.
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Jaison, check f 20 a red fuse in the under hood fuse block as described on previous post, it is Oxygen Sensors. Also, how did it go when you took it for a drive? You have a full set of spare fuses in the fuse block and inside the lid is the map to show where each one is, what size it is, and its purpose.

Let me know how it goes.
Here is a picture I took of the front HO2 sensor when I had the cradle out to stud the engine. The diagonal orange jack handle running diagonally at lower left is just below the sensor which is about midway up the jack handle. The aluminum block with the puddles of antifreeze is the ABS block. You can see from the top I think but if I recall you have to remove the air cleaner box and probably push the long radiator hose out of the way. Anyway, the ABS block is one the front driver side corner of the cradle so the sensor will be a little towards the center of the car above the front cradle cross bar. From underneath it looks to be above the point where the aluminum power steering return line crosses over the front cradle cross bar on the driver's side. Be aware that you are going to have AC lines, radiator fans, transmission connector, cradle cross member and numerous cables trying to occupy the same space as your hand when doing this, it will not be as accessible as it looks here.

Also, before you do all this, I would suggest you check the connector to the PCM (located inside the air cleaner box for cooling purposes) and the sensor pigtail to make sure that the connections are secure and undamaged. I would reseat the connectors on the pcm. Also, look for frayed wires from the sensor until they disappear into a wire bundle. The heater is controlled and monitored by the PCM.

Here is a close up of the sensor, I believe it is a 22mm socket or wrench. Be careful not to touch the business end (sensing bulb) when installing/handling the sensor. Don't forget to torque it if you can get a torque wrench in there. I did all 3 of my sensors while the cradle was in front of the car on jackstands, considerably easier than that which you are about to embark upon. Courage matey, there may be scraped knuckles and child inappropriate language ahead but you'll get it done. Before you embark on this I received a private message from Submariner409 that he would think about it and reply on this thread. I told him I wasn't certain I was on the right track (cat converter), you might want to give him a day or so to chime in. If you don't have the torque value I will try to look it up for you later today.

I think this is probably a 1 1/2 six pack difficulty level job when done in the car. May I recommend Heineken?
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Where do you live Jaison, I am in Kansas City.
Well, hopefully it will be nice and warm while you are working on it, beautiful country there.
Sounds like you are home free. How many beers did it take? LOL. Imagine how it would have been without the forum, I really appreciate these guys and gals.

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