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Discussion Starter #1
Vehicle:
2000 Mercury Sable
3.0 Liter Duratec 24V DOHC


Throughout the past few years I've done a lot of maintenance work. I include this information because that includes replacing old vacuum lines / coolant lines either as they failed or just going to the part store parking lot and swapping out old lines one at a time. Much easier than dealing with intermittent failures. Now, on to my problem.


I'm getting a code P1151. I've had it for a while, and the car is driving fine, but I would like to correct the issue. This seems to be an oxygen sensor lean code on bank 2. I would like to perform the following, and am unsure of the procedure in some cases, or the values I need in others.


Is it mentioned which HO2S sensor this is from the code?


Where is this sensor / both sensors located?


At this point, I am going to examine the wiring harnesses and the wiring for visual signs of defect, and I will repair if necessary. When doing this, can I take a reading across the pins and what value should I expect?


What should I look for next? It is quite likely that the sensor went bad, and I may need to replace it, but I would like to test and confirm if possible. Is there a procedure for this?


If I have to replace the sensor, I've heard they can be a PITA to remove. Are there any tricks for this?


Thanks for the info all!
 

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Discussion Starter #2
It has been a few days. Just a bump, hoping someone can help me get started, or perhaps rephrase the question.
 

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The sensor the code is referencing is the bank 2 (front/radiator) sensor 1 (upstream/pre-cat o2 sensor with a green elec. plug. It can be r&r'd with a 7/8" (22mm) combo wrench, o2 sensor socket or a crowfoot socket. It's the easiest of the 4 o2 sensors to access. I would 1st check its wiring/elec. conn. You may have an unfound vacuum leak causing that code. By the way, welcome from KCK!
 

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^^^^ Agreed. Likely cause is a large vac leak. LTFTs that are high positive at idle and drop toward lower numbers with the engine under load means vac leak.
 

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Discussion Starter #6 (Edited)
The sensor the code is referencing is the bank 2 (front/radiator) sensor 1 (upstream/pre-cat o2 sensor with a green elec. plug. It can be r&r'd with a 7/8" (22mm) combo wrench, o2 sensor socket or a crowfoot socket. It's the easiest of the 4 o2 sensors to access. I would 1st check its wiring/elec. conn. You may have an unfound vacuum leak causing that code. By the way, welcome from KCK!

Hey, thanks for the welcome! You are only a couple hours away from me. Now, for these sensors, is there any diagram that shows the location of the 4? I have not been successful as far as finding them. I think there is one mounted in the exhaust below the oil filter underneath the front. Would this be the sensor?


You really need to look at long term fuel trims to see if you have a vacuum leak before swapping the O2 sensor which is probably not bad.
^^^^ Agreed. Likely cause is a large vac leak. LTFTs that are high positive at idle and drop toward lower numbers with the engine under load means vac leak.

Okay, so I'm willing to do this, but my code reader doesn't read fuel trims like that. Is there a cost-effective device that will do this? Otherwise, is there a way to test that specific sensor? I do have a couple meters, a loop calibrator and an oscilloscope that are capable of reading / simulating the sensor value. Is this a voltage or a current signal from the sensor?


I currently have an Actron CP9575 but I'm pretty sure it can't record fuel trims.


Also, could you please give a concrete example of what I would be looking for with fuel trims? As I understand this, I will let it idle and see what the fuel trim is, then take it out on the highway, and record the fuel trim, then report the results back here for an analysis.
 

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Forscan. Free download for PC and pick up a LM327 for around $25 from Amazon. You will be amazed everything Forscan can do!!

Yes on the fuel trims. Be sure to get the info for both banks.
 

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^ ELM327. No need for a highway run. Note the fuel trims at idle, then depress and hold the accelerator to ~2500 rpm and read. With hood open, look behind and possibly to the right of the hood latch for a green plastic elec. conn. (plug). This will be the B2S1 o2 sensor. Fwiw, the 2 upstream (pre-cat) o2 sensors have green plugs and the 2 downstream (post-cat) o2's have blue plugs.
 

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Discussion Starter #9
Forscan. Free download for PC and pick up a LM327 for around $25 from Amazon. You will be amazed everything Forscan can do!!

Yes on the fuel trims. Be sure to get the info for both banks.
^ ELM327. No need for a highway run. Note the fuel trims at idle, then depress and hold the accelerator to ~2500 rpm and read. With hood open, look behind and possibly to the right of the hood latch for a green plastic elec. conn. (plug). This will be the B2S1 o2 sensor. Fwiw, the 2 upstream (pre-cat) o2 sensors have green plugs and the 2 downstream (post-cat) o2's have blue plugs.

Thanks for the info on Forscan. For now, turns out my scan tool can actually read the trims. I've uploaded a pic (-3.1) of where they are at idle, and the other is with the engine under load.
 

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I am thinking fuel trims don't look that bad but see what others think. You air intake temp is 61 degrees on one shot and 81 degrees on other. Were they done at the same time.
 

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I am thinking fuel trims don't look that bad but see what others think. You air intake temp is 61 degrees on one shot and 81 degrees on other. Were they done at the same time.

The first one was immediately after starting the vehicle and the second one was about 5 miles down the highway (I was traveling down the highway anyway).
 

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The first one was immediately after starting the vehicle and the second one was about 5 miles down the highway (I was traveling down the highway anyway).

Sorry I didn't read the temps right. Looks like both banks are identical on idle and under load which seem either very good or very strange.
 

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They are not always identical, though. They did vary at different times throughout the process. I ran it on a 20 minute drive. I have seriously replaced and checked the vast majority of vacuum components in this system over the last couple years. I have either replaced lines, replaced components, and I have been down to the heads (I have had the upper and lower intakes off twice and replaced the gaskets with new both times and torqued to spec).


That being said, I'm more than happy to follow diagnosis procedures from more experienced techs. I'm an electrician / machine control guy, so I understand how it goes.


So next, is there an expected reading at O2 sensor wiring I can take when performing visual inspection to verify power?
 

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So, I checked out my O2 sensor voltages on the way home. Turns out my scan tool does that as well. What I found was that the sensor in question is giving vastly different readings from the Bank 1 Sensor 1, and from both Downstream sensors. It is also not changing in the same manner as the other three. This doesn't rule anything out, but it does show that the voltage the PCM is reading is off.

Since I have to remove some stuff to check out the wiring, I'm just going to replace the sensor while I'm at it, and treat myself to an ELM327 device. I suppose that if I wanted to, I could check the voltage on the sensor wire itself and compare it to the scan tool's reading, but that would be pretty difficult to do by myself, and since I have to move stuff out of the way, I'll go ahead and replace the sensor.


Does anyone have/know the torque spec?
 

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Thanks for the info. My sensor sits under two metal coolant hoses, and the connector has the main fuse box under the hood mounted on top of it. I had to disconnect the alternator wire, pull up the fuse box and move it out of the way and disconnect a couple engine coolant lines to get access to the connector and inspect it. It took less than 5 minutes, so no biggie. The whole sensor swap only took about 45 minutes. I did give myself a good smack to the face when the sensor broke loose, though. At least it was my hand and not the ratchet directly.


Took it through two drive cycles, and it didn't throw a code. I'll know for sure tomorrow. That being said, the sensor voltage is now varying a lot more.
 

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My 1999 DOHC I cam at it from underneath the radiator. Use plenty of brake free. Still could not turn the sensor even with O2 socket. Ended up having friend hold a Pipe Wrench in place while I VERY slowly applied pressure with my foot. Do not rush the removal. Did half turn off and 1/4 turn on. Repeated to not damage the threads coming off and replacing new O2
 
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Jeff K
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