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Oxygen Sensors and CEL Codes...

W

WA2FAST

CEG'er
Joined
Mar 12, 2002
Messages
33
Location
MI
Hey there, so I am getting codes P0171, P0174, and P1151 on my 98.5 Contour SE 2.5L MTX. The CEL used to come on intermittently then go off, recently, it's just on, so I pulled the codes and that's what I got. Knowing cars and especially Fords very well, I realize that the codes suggest something else... like a dirty or bad MAF or vacuum leak. I cleaned out the MAF, checked for vacuum leaks, nothing changed... codes still came right back. I decided to clear the EEC's memory to kill adaptive and start over... well that was a very interesting thing actually. When I started the car, there was a good amount of exhaust fumes (white cloud) coming out and it smelled very strongly of spray paint which means (if I remember this correctly) that the exhaust mixture was ridiculously rich. I was watching the activity of my O2's and the downstreams were completely dead (.000) and one of the upstreams looked normal with quick switching, the other with very slow switching, and not that much change... at this time, the smell and cloud is getting ridiculous, so I took the car out to heat them up (sounds crazy to drive it like that, but heating up the O2's quite often wakes them up)... and sure enough, the O2's heated up at least enough to wake up the sensors. I was watching them and basically both downstreams are shot from the looks of it... one barely reads, the other is VERY slow switching if anything really, and at a very low voltage. The other (bad one) is also extremely slow switching which quite often isn't enough to throw a code but enough to cause issues and contribute to bad gas mileage.

So the bad O2 sensor list looks something like this...
B1S2
B2S1
B2S2
The short term and long term fuel trims are completely pegged out at fattening the mixture up, and as a result my fuel economy is shot. I've had O2's go bad on this car constantly... not sure why or what the design flaw is, but I've never seen a car "eat" O2 sensors quite like a Contour. Mind you, I have stock exhaust too. So my question is where can I get O2's for a decent price... the whole 65-upstream and 70-downstream is going to be quite a big hit here... any advise on where to get a decent price on O2's? Thanx guys, I appreciate it.
 
BTW, I know that these suggest a vacuum leak, but the O2's activity truely does show that 3 sensors barely move, if at all. I will check very carefully when I get home from the office today to make sure that there aren't any real obvious vacuum leaks (broken lines, rotted ends, etc.) but looking at the O2 activity shows that they aren't even trying. Is there a fuse somewhere for the HEGO circuit? I don't know if it's a fuse on this car (which I would assume) or a fusable link, but can someone tell me where I would find this to make sure that the fuse isn't shot for the heaters in the O2's? Thank you.
 
I was going to suggest getting a scanner that will graph the O2 sensor voltage. if they show little change then its a good bet that new sensors are needed.

Also you say it eats sensors, what ones have you been using?
 
They are the direct replacement plug-in type... I hate putting the universal ones together, it's a waist of time for only $5 less. I'll just pick up the Bosch direct replacement ones from Murray's today and slap them in when I get home... I do have a question though for you... do you know where the O2 heat circuit fuse is? I would assume it's in the fuse pannel under the hood by the battery, but do you know which one by chance? This is just in case... I don't like how BOTH downstream O2's were .000v till I drove it... that means that they are both REALLY shot, or possibly the heater circuits aren't working.
 
WA2FAST said:
They are the direct replacement plug-in type... I hate putting the universal ones together, it's a waist of time for only $5 less. I'll just pick up the Bosch direct replacement ones from Murray's today and slap them in when I get home... I do have a question though for you... do you know where the O2 heat circuit fuse is? I would assume it's in the fuse pannel under the hood by the battery, but do you know which one by chance? This is just in case... I don't like how BOTH downstream O2's were .000v till I drove it... that means that they are both REALLY shot, or possibly the heater circuits aren't working.
Click to expand...


I agree about the plug and play vs $5 ...


the heater fuse is in the panel next to the battery. However you would throw a code if it was blown.

also the lower O2 sensor do take time to start reading. On a cold start up they are going to read zero for awhile. Then their voltages should sit on top of the up stream sensors while at idle. off idle they should follow the upstream sensors but they will not be the same.
 
also keep in mind that the downstream sensors shouldnt really be switching if the cats are doing their jobs. they should stay pretty steady, only moving slightly once warmed up.
 
Gotchya... and yes, I know that they do take a few to heat up from the exhaust gas... but the EEC is still throwing codes that suggest both are shot. Maybe I will buy all 3 sensors, just replace the upstream one first, reset the computer, and see what happens. I was just blown away by the ammount of white exhaust (like steam really) that was coming out after I reset it yesterday... until the car warmed up, it smelled terrible and there was a noticible ammount of smoke (steam). Bank 2 was pegged at 99% fuel adder (that's relative to the adaptive range of course) after 5 minutes of driving too... so that's what really got my attention and also explains my fuel consumption.

You are right, I forgot that there is a code for an O2 heater circuit failure (AKA, wire is broken, heater in the O2 has failed completely, or there simply is no O2 plugged in)... thank you for clearing that up for me.

Thank you again for your help... I'll get all of them first and just try the upstream and see what happens, then worry about the downstreams... they are much easier to get to anyway.

Just for clarification, bank 2 is the front of the engine, radiator side, right? I can't believe that my car is making something "easy" (again, relatively speaking) on me for a change... maybe it's getting nicer in it's old age?
 
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replace the upper sensors and reset the PCM again. if its still running lean after that double check for vacuum leaks, check the MAF and IAT sensors.

also, while highly unlikely, a cracked exhaust manifold before the upstream O2s can cause the PCM to think its running lean. i say highly unlikely because both manifolds would have to have cracked.
 
Thank you for the advise striker2. So you are telling me that with those codes and with the activity that I was looking at with the O2's to replace both upstream sensors? Bank 1 Sensor 1 (upstream) looked pretty normal in regards to how it was switching.

I will double check the vacuum leaks for sure, already checked/cleaned the MAF yesterday too... that's freshly cleaned and I obviously verified that the o-ring was in good shape, and it's been re-seated and installed correctly, so I should be just fine with the MAF.

I know what you mean, a cracked or leaky exhaust manifold gasket can do the same thing but I'd definitely hear an exhaust leak, I know that dreaded "tick" from a header... this car doesn't have that at all. I agree... both would have to be cracked, so that's highly unlikely anyway.

Which sides are the banks on again? I can't remeber what side is which.
 
bank 1 is the firewall side. i would replace only the bad one first, then reset and go from there.

its still sounds like a vacuum leak since both banks are lean. double and triple check all the hard plastic vacuum lines as they can become very brittle and can sometimes break from even the slightest movement. also check the valve cover breather tubes and the PCV tube. since they are after the MAF, a leak would cause the engine to run lean.
 
Will do, thank you Striker... I appreciate it. I will once again check the vacuum lines and all vacuum connectors/seals and make sure it all looks good, I do agree, it does sound like a vacuum leak, but I don't hear a hiss or whistle that's usually associated from a manifold gasket (pretty unlikely anyway since it's never been taken appart), nor did I see anything but I will double check again. Thank you again for your help and I'll let you know what I come up with.
 
I slapped the scanner on it at lunch and after 15 minutes of driving, it really revals a lot by just watching the O2's. The downstreams seem to be fine... they look nice and active (in their proper range once everything is heated up to normal operating temp). At first, both upstreams look good too but after the car has warmed up, Bank 2 upstream slowly decreases all of the way down to .030v and just sits there (even with my foot to the floor and the other is reporting the proper rich voltage in the .9xx range). The funny thing is that the rear O2 is picking up the fact that the upstream O2 isn't working on Bank 2. As the upstream stops cycling and starts to just sit and gradually go down, the rear O2 does the same thing, but up. By the time I was done with my 15 minute trip, the front O2 was at .030v and the rear O2 was at .965v. No check engine light yet, but the long term fuel trim is up like 15% at idle or something on bank 2.

Bottom line, I'm going to replace bank 2 upstream and go from there... I'll let you guys know later how everything ends up, thank you all again for your help, I really appreciate it.

I'm still going to go over all of my vacuum lines and make sure that I don't have any leaks too... Although that one O2 is clearly bad, I want to rule out vacuum leaks or gasket issues before spending any more money.
 
Update:

Update:

Okay, so I pulled the fuses to reset the computer, swapped out the Bank 2 upstream O2 sensor (right next to the oil filter), and checked for vacuum leaks. The O2 install went just fine outside of the plug being a PITA to get plugged back in (dumb location for that plug). Once I pulled the top half of the air box off to be able to get to the vacuum hoses better and be able to check everything out, I figured I'd change the PCV for good measure, so I did that too.

I ended up verifying that every single vacuum hose is in great shape, plugged in, no cracks or breaks, rubber is in surprisingly good shape, etc.

The only place that concerns me for a vacuum leak would be the tubes coming out of the intake manifold right on top. The one going to the brake booster seems pretty good but the other one (the smaller one) that gets split for everything behind the intake is pretty shady. I think it's crazy how a hard plastic locking ring thing is supposed to seal against aluminum and another hard plastic connector.

Without a doubt, this is a bad "seal" and is a good source of a leak. It probably isn't real bad, but enough for me to want to replace it. My question is this, where can I get the little plastic locking ring for that vacuum tube? I'd actually like to replace both of them for good measure since the car has 142k on it and they are both questionable, not to mention, I can't believe that this was the final design there.

Can I only get these at the Ford dealership, or can I get them at my local auto parts store?

Thank you again guys, you have been a huge help once again. It's really too early to tell what the car is going to do, but so far, the O2's are all very active and seem to be doing their job just fine now. Hopefully after replacing these little plastic locking rings, I won't have any further issues with this.
 
I pick that stuff up at the junkyard if I find it in good shape and gently pry out with a small hook/pick. At the Ford dealer you have to buy the brass insert with it. Not the cheapest for sure.
 
the plastic clips do not seal the tube there is a rubber O-ring down in the hole that actually seals it. the plastic clips just hold the tubes in. hope that helps you.
 
Haha... okay, well theres a vacuum leak then because all I have is a plastic retaining clip holding both lines in place, and when I remove them, you can see the plastic retainer and machined aluminum... no rubber o-ring.

I don't have any junk yards around me that I am aware of, so does anyone have a part number or an actual name for these parts from the steelership? When you say that they aren't cheap... what kind of price am I to expect?

Thank you all again so much for the help, I really appreciate it, I guess I'm on the road to getting this all buttoned up, but I guess I need those clips/seals from the dealership. Does anyone have a part number or an actual name for them? Thank you!
 
All better

All better

It must have been that one O2 that was causing all of the trouble. I've put over 300 miles on the car since the O2 change and the CEL is nowhere to be seen thankfully. I would still like to replace the seals for the 2 vacuum lines coming out of the top of the intake manifold, so does anyone have a part number on these? I know that if I just walk into the dealership and try to explain it, it's going to take 45 minutes before we find it on the computer... so can anyone help me out with a part number? The larger of the two is the one that I know for a fact needs to be replaced, but I might as well just do both for good measure. Thank you, any help on that would be appreciated.
 
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