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need help figuring out what the problem is 2000 Deville

10012 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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Would a clogged catalytic converter or bad catalytic converter give me a DTC?
A clogged CAT usually won't. The engine just can't exhale so it will run poorly if at all. A bad (ineffective) CAT should set a DTC.
Yes, a flashing SES light means severe misfire detected.

A clogged CAT would present driveability problems at higher speeds and RPM's as the engine would have trouble exhaling, so to speak.

I don't trust Bosch parts and that causes me some concern.
Have you ever checked for a ripped plenum?
OK, you know that the plenum duct is the rubber coupler between the TB and the manifold. It usually develops a rip on the bottom where it cannot be seen. With the engine at idle, spray some Brakleen or such under the plenum while flexing it with your finger to open the rip (if there is one). If there is, the RPM will increase.

The fuel rail remains under pressure once the engine is shut down for quick starts. Look for the schreader valve on the fuel rail (looks exactly like a tire valve). Remove the cap, hold a rag over the service port and bleed off the pressure (just like letting the air out of your neighbors tire). You may get a about an ounce of gas out of it.
Improvise. Use a screwdriver, dowel rod, anything that will flex it a bit.

Usually a ripped plenum will set a P0171 & P0174.
If you are talking about a cooling system pressure test, that will rarely detect a bad HG unless it is already so bad that it is so obvious that a test is not needed.
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