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Old 02-06-2007, 16:27   #1 (permalink)
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confused O2 sensor fault code masking another problem?

I am on my 3rd OEM replacement O2 sensor in a few months. The Ford garage can't seem to explain why this is the case. I originally posted this problem under a different thread in September of 2006, and the codes that hEATFocus deciphered in that thread, (thanks again), are the ones that have always come up after the diagnostic again and again.

Presumably my cats are okay, no funny stench, exhaust is solid with no holes and the motor is functioning fine. Other than that, does anyone have any theories and or remedies? Anybody else have this problem? I have owned nothing but Fords, and this is the first chronic O2 sensor problem I have come across. I'm getting frustrated by this super pesky problem and risk punching the light out and causing an accident on my to work in the morning.......

Please help!

Eric
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Old 02-06-2007, 18:31   #2 (permalink)
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Re: O2 sensor fault code masking another problem?

There are a few things that can "kill" an O2 sensor.
Electrical problems that cause the sensor to short out, exposure to lead, if your car is burning oil (high oil consumption) it can contaminate the sensor causing it to fail, if your car is running rich over a period of time it can deminish or destroy the sensor, also antifreeze or oil on the outside of the sensor can harm it.

Is this an upstream (before the converter) or a down stream sensor (after the converter) that keeps failing? If it is a downstream sensor, then the code you are getting maybe because of a bad converter. The sensor is after the airflow from the converter, so if the converter threshold is bad, you could get a code from the sensor because it is reading what is coming out of the converter.

Another problem could be and intermittent sensor ground.

A friend of mine went through 4 sensors before they found out that the voltage going into the sensor is not stable. In this case the voltage comming from the sensor will be too low at times and the check engine light will come on.

Hope this helps a bit, Eric.
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Old 02-06-2007, 18:43   #3 (permalink)
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Re: O2 sensor fault code masking another problem?

It has been the downstream sensor all three times. I definitely agree with the possiblity of oil consumption continually fouling the sensor, yet the car has 55k on it and is in excellent condition otherwise as I am always on top of tuneups and scheduled maintenance.

Cats seem to be good, as I stated above, is there a way to tell if the converter is bad other than the smell or a failed emission test?

Here are the three codes that always come up:

P1000 just means the computer was reset recently and will go away after a few driving cycles. Nothing to worry about there if the computer was reset recently to clear a code or the battery was disconnected.


P0136:
P0136 - HO2S Sensor Circuit Malfunction (HO2S-12) The downstream HO2S sensor(s) are continuously checked for maximum and minimum voltages. The test fails when the voltages fail to meet the calibrated limits. Pinched, shorted, and corroded wiring and pins.
Crossed sensor wires.
Exhaust leaks.
Contaminated or damaged sensor.

P1138:
P1138 - Lack of HO2S-12 Switch, Sensor Indicates Rich See DTC P1137
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Old 02-06-2007, 20:05   #4 (permalink)
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Re: O2 sensor fault code masking another problem?

Here is a link to testing the converter. Catalytic Converter Testing

Quote:
P0136 - HO2S Sensor Circuit Malfunction (HO2S-12) The downstream HO2S sensor(s) are continuously checked for maximum and minimum voltages. The test fails when the voltages fail to meet the calibrated limits. Pinched, shorted, and corroded wiring and pins.
Crossed sensor wires.
Exhaust leaks.
Contaminated or damaged sensor.
The P0136 code that you are getting is usally a wiring issue. The sensors that you have bought so far, did they come with the wiring harness already on it, or did you have to splice it and reuse your old harness? How many wires do you have running to your O2 sensor? If you had the work done at the Ford place then you probally have the one that has the harness on it. Was not clear on if you had it done there or if it was a DIY project.

Concerning P1138 (found this when looking into that code)
Lack Of HO2S1 Switches, Rich (Bank 1, Sensor 2)
These codes usually do not indicate a problem with the O2 sensor. Rather, the O2 sensor is correcting lean due to an overly rich air/fuel ratio. Check Base Engine Idle, EGR, Fuel System and Air Induction System.

I am going to look into this a little more for you and see what I can dig up. Those two codes together and seeing it is the downstream sensor that is picking up a lean fuel mix instead of a rich one makes me scratch my head.
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Old 02-07-2007, 14:13   #5 (permalink)
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Re: O2 sensor fault code masking another problem?

Easiest way to check cat efficiency is via datalogger, monitoring up and downstreamers & with engine at full working temp, hold the revs at 3000 for several minutes, if the downstream hego starts switching as much as the up then the cat is faulty.
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Old 02-07-2007, 19:32   #6 (permalink)
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eek Re: O2 sensor fault code masking another problem?

Just a note! I drove for several weeks on my 02 wagon with a bad sensor @ the cat and it changed the shift on the trans, ford service said it was in the computer and it would relearn by it's self it did 20,000 miles later ,so don't let it go to long! by the way the sensor was bad from running over a branch and streching the harness thus breaking the wire where you couldn,t see it under the heat cover.
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Old 02-08-2007, 11:17   #7 (permalink)
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Re: O2 sensor fault code masking another problem?

Ok guys, Bosch O2's all three times, no splicing or anything crazy like that. Connections are secure, wiring is fine. I don't think it is the O2 sensor, and with everything else presumably okay, what's the deal?

I am tired of getting robbed by the dealership, it's $100 just to hook up and so far no cure.

Thanks for your help!!
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Old 03-02-2007, 21:24   #8 (permalink)
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Re: O2 sensor fault code masking another problem?

Quote:
Originally Posted by Fordtech.
Easiest way to check cat efficiency is via datalogger, monitoring up and downstreamers & with engine at full working temp, hold the revs at 3000 for several minutes, if the downstream hego starts switching as much as the up then the cat is faulty.
Listen to this fella.
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