Contour Enthusiasts Group Archives Forums General Troubleshooting Simple question about oxygen sensors...

I'm trying to find the voltage range for the O2 sensors (front or rear, either bank). I'm getting a range of .03-.90 V, and I thought that looked a little funky. Only reason I ask is because I'm still battling the PO171/174 and decided to do a quick test on the sensors. I also got a failure on the DPFE downstream hose test (verbatim from the scanner TestID $41 Fail, ComponentID $12, Fail High, FFOF not<= 0200, Delta Pressure for Downstream DPFE Hose Test ).
I know that the upstream sensors should be switching rather quickly, but should the downstream sensors be switching about as fast? Also, I've heard that the DPFE sometimes gets condensation in it, which causes a short and a bad reading. This stupid code has me absolutely stumped, and I'm out of ideas. Before anyone asks, I have done a full UIM/LIM rebuild, replaced quite a few vacuum lines, gaskets, and haven't found any leaks. I also did the plugs/wires, filters all across the board, and cleaned the MAF. Could bad O2 sensors, along with the failed DPFE cause a PO171/174, or would that come back as an EGR failure?
I'm stumped for the first time on this car, and am asking for any help/suggestions that any of you have! Emissions are due at the end of the month, and as of now, it will most definately fail!
Thanks,
Sean

Sensors after the cat should switch slower than before the cats (less fuel in the mixture, if the cat is doing its job)


I will look for values..


Ray

The oxygen sensors should have a range of 0 to .9 volts. 0 is lean, and .0 is rich. The downstream oxygen sensors should switch much slower than the upstream sensors unless the cats atr dead. The downstream oxygen sensors job is to monitor the cats. A cat that works well will have more even readings or you might say that the cats dampen the readings. When the rear sensors switch at about the same rate as the front sensors, the cat monitor in the PCM will set a code and turn on the check engine light. The cat monitor only runs ocassionally after several conditions have been met.

Fix the EGR problem then retest to see what you have.

Thanks Ray and Jim,
It better not be the pre-cats since they were replaced at 79k (good thing they were done then). I'm going to do some more tests this weekend and see if anything else comes up. Otherwise I may just try the MIL eliminators for now just so I can pass for now.
Ever get those fuel lines sorted out Ray?
Sean

MIL eliminators do not change the ACTUAL emissions of the pipes.

They only fool the PCM in to thinking that the downstream is still working.. (its a fake circuit that switches really slow...so it THINKS it is an o2 sensor). the ACTUAL emissions are still going to be whatever they were.


and re: fuel lines.. I got the coupler off.. I am going to get two replacement hoses with the couplers already on them from a donor car on Saturday, thanks to a couple of good friends from SC forums. (really good guys..)
thanks for asking, btw.. I appreciate it..

Ray

Oh, I already knew that. I just wanted something to turn the CEL off for the time being. New cats should be able to pass emissions (in theory). Thanks for the heads-up though!
Sean

Please let us know what you come up with as a solution. I have the same two codes on my car and it's driving me crazy. Isn't it unlikely that two O2 sensors would fail at the same time? Could the EGR valve be the problem? I've already replaced the IAC valve to no avail.
Thanks,
LLL

I'm working on it tomorrow morning, but as soon as I get any new info on it, I'll let you all know! I put an excerpt from the Windstar forum down below. It seems kinda relevant to the problem you (Louie), and I have. This is what I'm doing tomorrow. As for the O2 sensors, I have no idea since my electrical experience is nowhere near my mechanical experience. Ray, Jim, anything to add?

Windstar Forum

"Posted by wrestler
REMOVE | ALERT | EDIT 31-Jul-03 at 08:51 AM (ET)
@ 577

Please, folks...if you get a recurring P0171 code, or anything pertaining to EGR flow, and the engine is running okay, remove your EGR DPFE sensor, tap it in your hand with the ports DOWN and you will see moisture. This is condensation that gets trapped in the EGR tube. (BAD DESIGN!)

As you start your engine in the mornings (especially humid), you blast all that moisture into the sensor because the EGR valve is closed at idle. It shorts out, giving you a light, and that stupid code.

One remedy, although repetitious, is to spray the sensor innards with computer cleaner. Do that, reinstall it, clear the code (disconnect battery, then reconnect), and it won't come back for a while. This will keep you from wasting any more money on new sensors. There's nothing wrong with them...it's a bad system design problem.

I'm working on my own solution to this, (since Ford is either unwilling or unable to) which will be one or both of these steps...
1) Relocate the sensor with longer hoses, and extended wire
2) Add a small vacuum line directly from the "High" side hose tap to the intake manifold to provide a constant vacuum source which will continuously draw off the accumulated moisture before it makes it to the sensor.

I'll keep you posted on how this works out. In my case, it's the ONLY item that triggers that damned light."

All along I thought us Contour owners had it bad! Those Windstars seem to be plaqued by each of our problems, plus their own unique ones! It's another place to look since I've completely ruled out a vacuum leak (I've put pressure, and vacuum to everything possible). Good luck, and you can expect a reply from myself sometime tomorrow around noon. Goodnight!
Sean

Good Luck, Sean. Jeez, I hope that's the problem.
Has your engine been pinging on hard acceleration like mine?
LLL