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Old 04-03-2010, 03:07 PM   #1
bamboozer
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Upstream oxygen sensor

2001 Focus SE wagon, ZTEC engine.Engine light came on, had it checked at Autozone and the verdict was the Oxygen Sensor closest to the exhaust manifold. I replaced it but the light came back and I could not pass emissions for inspection. I replaced the sensor as a warranty, the light went out and the car passed inspection. Joy was short lived as the after about 200 miles the lights back on, not sure but I'ts probably going to come up as the sensor again. Any ideas?


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Old 04-03-2010, 06:08 PM   #2
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As I'm sure others will respond - it's best to get the 'exact' code from the OBDII for further response and analysis. That will provide the greatest insight with a CEL.
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Old 04-03-2010, 08:19 PM   #3
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what brand of sensor are you buying? mine seems to ear bosch sensors for some reason
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Old 04-08-2010, 10:35 AM   #4
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Code is P0171, I believe that indicates the sensor closest to the head. Both replacement sensors were Bosch. They seem to last a little less than a month. Connections are clean and correctly placed away from the manifold. Thanks!
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Old 04-08-2010, 10:50 AM   #5
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i have a ford sensor for sale for cheap, you may want to give it a try, check the link in my post and pm me if you want, motocraft sensors are the way to go
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Old 04-09-2010, 09:16 AM   #6
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Thanks for the offer but I intend to keep warrantying the Bosch Sensor until I either get mey money back or fix the problem. The trouble code has remained the same thru out, it's got to be the part.
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Old 04-10-2010, 03:19 PM   #7
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i had some probs with my o2 sensors or should i say i pulled one of the codes for the o2 sensors. turns out it was an exhaust leak in front of the upstream o2 sensor. a vacuum leak can cause that too.
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Old 04-10-2010, 03:21 PM   #8
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i just looked up that "P0171" code and it turns out that was the same dtc i was getting. i remember my xcal saying the o2 sensor was stuck/biased lean, causing my zetec to run rich all the time. it just thought it was lean bc of all the o2 getting in the exhaust leak. at first, i just changed my o2 sensor and just like you said, a little ways down the road my CEL came back on.

what kind of exhaust mani do you have?
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Old 04-10-2010, 05:00 PM   #9
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Quote:
Originally Posted by bamboozer View Post
The trouble code has remained the same thru out, it's got to be the part.
P0171 has very little if anything to do with a faulty O2 sensor according to your DTC. It's usually associated with a lean condition as the result of, most commonly, a vacuum leak. This would be consistent with the fact you replaced the O2 sensor and it didn't resolve your problem. Look for induction leaks - unmetered air that is entering the system after the MAF. Full DTC definition and possible causes follow:

P0171 - System Too Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. For lean and rich DTCs:

Fuel system
Excessive fuel pressure.
Leaking/contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Vapor recovery system.

Induction system:
Air leaks after the MAF.
Vacuum Leaks.
PCV system.
Improperly seated engine oil dipstick.

EGR system:
Leaking gasket.
Stuck EGR valve.
Leaking diaphragm or EVR.

Base Engine:
Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2Ss.

A SHRTFT-1,2 PID value between -25% to +35% and a LONGFT-1,2 PID value between -35% to +35% is acceptable. Reading beyond these values indicate a failure.
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Old 04-11-2010, 11:27 AM   #10
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Quote:
Originally Posted by BC_ZX3 View Post
P0171 has very little if anything to do with a faulty O2 sensor according to your DTC. It's usually associated with a lean condition as the result of, most commonly, a vacuum leak.
i agree with^, i would check for vacuum and exhaust leaks first.
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