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  #1  
Old 06-20-2015, 11:51 PM
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p0171 1999 grand cherokee

Quick question
I have a 1999 WJ GCL with 4.0 that was running well but oozing oil out of rear main seal, and obviously stinking and smoking from engine compartment due to oil leaking onto tail pipe that runs under rear of engine.

I just replaced rear main seal and oil pan gasket. Since, been having idle issues. It doesn't idle steady and occasionally idles roughly.
Today p0171 just popped up. It is the only code, and I have checked it multiple times. My question is if i could have messed up the wiring to o2 that is causing lean run?

I do have a scan tool capable of live monitoring, what should I be looking for?

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  #2  
Old 06-21-2015, 07:18 AM
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Re: p0171 1999 grand cherokee

P0171 is indeed the code for a too lean bank 1. It means that for some reason too much oxygen is measured at the 1-1 oxygen sensor. Since the upstream O2 sensor is used for the fuel trimming, it is a good idea to check the wiring of this sensor for damage (cut isolation/isolation resting against hot exhaust part).
If the wiring seems to be ok, then I would put the scanner on it and check what the 1-1 sensor is doing in live data. It should jump up and down between 0.2-0.8V and the faster this change the better. With a lean mixture, there is too much oxygen in the gasses and the O2 sensor will read in the lower range(0.2-0.4V). But if the PCM sees this, he will uptrim the fuel injector pulse until a certain maximum. I'm not sure at which point the P0171 code will be set, but when you look at the fuel trim figure STFT (short term fuel trim) for bank 1, you will probably see a figure of more then +20. (While it normally should be below +10 and infact you should see it go from +4 to -4 more or less).
If the O2 reading is fixed at 0.2V or if its even shorted and reading 0V, then there still must be a shorted wire to ground, or the sensor itself is bad
If you don't find anything special till now, then some other problem is happening. Could be an exhaust leak before the sensor (cracked manifold) or problem with MAP sensor.
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Old 06-21-2015, 11:28 PM
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Re: p0171 1999 grand cherokee

I am not going to have a chance to check wiring till Tuesday some time. I can and will further check live data with scanner. I briefly looked at it this AM and saw the stft at 1/1 as going between 21 and 35. I didnt write down voltages. I know the cel was on last night, off this morning, then came on again on the way home from work while waiting for a coffee.
Just to be clear, o2 1/1 is the upper closer to the front of the engine?


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Old 06-21-2015, 11:43 PM
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Re: p0171 1999 grand cherokee

Yes, the 1-1 sensor is the sensor closer to the engine exhaust manifold. Your jeep only has 2 sensors?
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Old 06-21-2015, 11:45 PM
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Re: p0171 1999 grand cherokee

Actually it has 4. With ca emissions there are 2 cats right up close to manifold.


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Old 06-22-2015, 02:30 AM
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Re: p0171 1999 grand cherokee

Ok, then the O2 sensor above the forward cat is the 1-1.
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Old 06-22-2015, 07:19 PM
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Re: p0171 1999 grand cherokee

So inspected wiring to o2 #1, nothing looks hinky.
Cel has gone off and come on a couple of times in last couple of days.
Hooked up scan tool after driving to work the other day ( 20 minutes mostly highway) and st ftrm showed around 20 + - . Hooked up scan tool today after driving home from work ( again, 20 minutes mostly highway) and all numbers were what you listed as normal.
Voltages were popping from 1-8 constantly changing this time. I didnt write down what they were doing the other day.
As this issue seems to be with bank 1 o2, and the wiring runs no where near the oil pan or anything that i was working around while doing oil pan gasket and main seal, i dont believe it has anything to do with work that i did 2 weeks ago unless i somehow bumped into wires while wrenching on something below.
Correct me if I am wring, but, from what you have said so far, it would seem that i need to look into replacing the first o2 sensor.

Thoughts??



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Old 06-22-2015, 07:47 PM
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Re: p0171 1999 grand cherokee

It would be nice to see what the 1-1 sensor is showing when the problem is there. If the voltage still bounches up and down, or that it stays at a fixed voltage.
You will have to be carefull driving with this problem, because if the PCM sees a lean mixture, then it will add fuel to the normal injection schedule. You can see that at the + sign in the STFT figure. If it is a real lean mixture, then the added fuel will not harm, but if its wrongly seeing a lean mixture, then it will add too much fuel and that will be burnt of in the cat, which could damage the cat internally.
Since only bank 1 is showing a lean mixture, the problem should be related to a sensor from bank 1 only. If you didnt see any cracks in the exhaust manifold or any opening where fresh air could enter the exhaust, then it probably is a good idea to change the 1-1 sensor. Many say that when one sensor fails, you better change both upstream sensors, because the other sensor will probably give problems soon as well, since it most probably is as old as the other one.
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Old 06-22-2015, 08:43 PM
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Re: p0171 1999 grand cherokee

I have had exhaust manifolds with cracks, and there is a definite sound to an exhaust leak. There is none of that.


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Old 06-22-2015, 10:18 PM
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Re: p0171 1999 grand cherokee

I am finding 56041212ae as the oe part number. Are both upstream sensors the same? And am i really better off buying a chrysler/mopar part?


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Old 06-23-2015, 02:38 AM
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Re: p0171 1999 grand cherokee

Both sensors are the same, however the connectors and wire lenghts are not. So they are not interchangeable.
The OEM sensors are from Denso, so you can buy much cheaper Denso sensors online. I paid around USD 26 for each sensor, but donīt remember where i bought them from.
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Old 06-23-2015, 08:40 AM
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Re: p0171 1999 grand cherokee

I have to say, the denso sight to determine correct part is not super clear.
I am seeing 4 part numbers with no definite description.
234-4076 / 4077 / 4079 / 4115

They dont say which goes where or what length wire. And only 4079 has different connector.

And i am also finding sites saying that ntk is oe part.


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