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Lowering frame to change rear HO2S, pull on front head bolts?


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Fantastic, good job, and terrific that you didnt give up!

Hmm, I will be interested in what others say, but you may have a leaky injector. Have you used Techron?, if not try a can on a full tank per the directions

How is it running? It may take some time for the PCM to adjust, what do you all think about disconnecting the battery?

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By the way, I can not believe that you can get snow under the hood so badly,

Check the seal along the cowl that contacts the hood to make sure its in place

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It runs great as far as I can tell. I wanted to drive some more before drawing any conclusions, but when I tried to hit the throttle from idle (in neutral) it may have responded more quickly and without any hesitation compared to before. It also used to sometimes shudder slightly once every few seconds at idle, but now it idled smoothly when I tried. But still, I want to drive some more before saying anything definite. I cannot get Techron where I live. ST-1 fuel injector and combustion chamber cleaner is the closest I can get. I have used that before, but that was several years ago. Is there a way to diagnose a leaky injector?

As far as I know, the seal contacting the back part of the hood is in place, including the two soft pieces on the sides. I was also quite surprised, but we did have a real snow storm with lots of snow and strong winds. Since it was also quite cold, the snow was very light and fluffy, and consisted of very small snowflakes. Basically like a powder, which blows into places much easier than "normal" snow. Maybe that was why it got in there so much. I have never seen snow there before (and I do routinely open my hood quite often).

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I have edited my post with pictures above to also include a picture of the tool I used.

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Dont worry about the leaky injector until you see the rich code again maybe that was nothing and a remnant of the O2 sensor problem. Disconnecting the battery to let the system relearn was probably advised

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Glad you got it fixed. Parking the car with the front against the wind can result in the engine compartment getting snow in it.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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When i did mine from up top i didn't remove anything,i rented the tool from advance auto parts and used a long extension.

What kind of tool did you use? If you could use a "normal" tool (i.e., a socket that is deep enough to fit over the sensor, and has an opening cut in one side of it to allow it to be slid onto the sensor from the side), it seems like they improved on the serviceablility of the sensor for the newer cars, which is a good thing (it is more often the other way 'round).

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Unfortunately, I am not done with this job yet :(, and I will try to describe the present status in as much relevant detail as possible. It is a lot of information, but I think it is better to have all of the info available.

I should have read the book more carefully. P0138 means a rich condition for sensor 2, bank 1, in other words for the sensor upstream of the catalytic converter. I have not touched that one, only the two in the manifolds are changed as of now. Going for another drive today, the code and SES light came back. I am now wondering if it is just an unlikely coincidence that this just happened to appear right after changing the oxygen sensor, or if it somehow related. Looking at the oxygen sensor switch times with my OBD Link scan tool and computer, things get even more puzzling.

Sensor 1 Bank 1 (rear manifold, brand new, the one I just replaced): about 20 ms to switch in either direction, lean to rich or rich to lean.

Sensor 2 Bank 1 (pre cat, the one giving P0138, old): about 20 ms.

Sensor 3 Bank 1 (post cat, old): has no value, since it does not switch back and forth (the one after the cat should not).

Sensor 1 Bank 2 (front manifold, almost brand new, replaced about 1.5 weeks ago): about 70 ms -- a lot longer than the other sensors.

The P0138 code appeared after replacing Sensor 1 Bank 1 (rear manifold), which seems to be operating well.

The old Sensor 2 Bank 1 that set the code seems to be working well, at least looking at the switch times.

Sensor 1 Bank 2 appears to be somewhat sluggish, even though it is new. There was no trouble after that one was replaced, if anything the idle quality and throttle response improved already after replacing just that one.

When the light came back on, the only PCM code was P0138 when I scanned it using the DIC. When I used my scan tool, I could see not only P0138 as history (it had changed from current to history when I checked the codes), but also P0300 (misfire detected) and P0305 (misfire cyl 5) as pending. I guess that means that the PCM has seen some indication of misfire(s), but not enough to actually set any code yet. I double checked with the DIC, and they did not show up there. After clearing the PCM codes with the DIC, they all disappeared, including the two pending ones that I could only see using the scan tool. Cyl 5 has been misfiring before, setting P0300 but not P0305. That was some years ago, and was fixed by replacing the plugs. Plug number 5 was severely fouled with what looked like oil deposits, and one of the platinum tips was missing. After plug replacement, everything was fine, but I think that cyl 5 may have a worn valve guide that makes it burn oil. It is not visible in the exhaust, but because of the fouled plug I still suspect it. It seems unlikely that this would cause the P0138 however, because I have not noticed any misfiring now (it was very noticeable the last time, and then there was no P0138 code).

Back to today: Fuel trim was 13.0 for one bank, and 13.2 for the other. I do not remember which was which, but since they are very similar, I take that as an indication that they are good. During the very limited driving that I have done, I have not seen any degradation in fuel economy. It seems to be the same as before (a rich condition should result in worse fuel economy).

I do not know if it has any importance, but before replacing the sensor, I had an almost-dead battery situation. When I turned the key, the starter moved very slowly. After a few seconds, things started to flash, and there were sounds similar to static (cracks and such) coming from the radio, even though the radio was turned off. It seemed to happen when the voltage got too low. I had to charge the battery for about 5 minutes with the other car before I could start, and even then only barely. Once started, it ran fine, and I went to the store and back to buy the crow's foot wrench. There were no codes or MIL during that trip (well, some memory loss etc codes from disconnecting the battery, but no P0138). After that, the car has started fine, but I think that my battery is weak, and I am looking to replace it. Opening the doors and trunk every now and then (during my first three-hour unsuccessful attempt at changing the oxygen sensor) should not be enough to drain the battery.

I am now trying to find possible causes, diagnosis methods and ways to fix it. As always, I am thankful for any help I can get.

/Jonas

edit: I thought the first sentence could be misinterpreted, so I clarified it.

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I just went out, disconnected the battery, and replaced the plug in cyl 5. It was quite caked with deposits, so that was a good thing to do. First, I warmed up the engine by idling for a while, reading codes and checking things before taking off. The only PCM code present was P0603 (PCM Memory Reset), but I guess that is expected after having disconnected the battery. After driving about 10 miles, I stopped to turn around and check the codes. I then had

PCM P1139 HO2S Insufficient Switching Bank1 Sensor2 CURRENT, with no MIL lit.

I shut off the car, waited a few minutes, restarted it and continued driving. After a few minutes, the MIL came on, and when I checked the codes I had

PCM P1139 CURRENT

PCM P0138 Circuit High Voltage Bank1 Sensor2 CURRENT, again indicating a rich fuel ratio reading from that sensor.

I continued driving, and when I got back, I had

PCM P1139 CURRENT

PCM P0138 HISTORY

Unfortunately, I did not have my code reader with me this time, so I could not check the switch times.

I am starting to lean towards the pre-cat sensor being the culprit. The only thing that does not quite add up is that it seems odd that it would appear like this now, going from no indications at all to codes and MIL on every trip. Any thoughts?

/Jonas

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I looks like you have got the problems figured out. the sensor will be cake if you ever have to do it again due to the narrow body of the sensor compared to the original. much better. by chance was the hood popped when it had all the snow under there or was it latched tight? just curious because that is alot of snow

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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The hood was latched tight, fully closed. I was also surprised by the amount of snow.

I plan on getting two new oxygen sensors, pre and post cat. I have a theory for what could have happened: maybe with the two new sensors in the manifolds, the PCM can swing the fuel mixture faster back and forth (the faster, the better control), and now the old sensor in front of the cat cannot keep up. At least the two sensors around the cat should be much easier to access. The only problem is that I have to get in under the car, but that is something that I can cope with (probably by renting a lift at a gas station, there is a chain of gas stations in Sweden that has DIY lifts). Do you think it could be a problem if there is a few minutes gap between engine shut-off and unscrewing of the sensors (that they would be hard to get loose)? It takes a little to get the lift up, and it is also indoors, so I cannot really idle very much in there.

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I have removed that sensor a couple of times and as long as the muffler system is warm that is fine, once the car is on the lift before it goes up run it for a few minutes it will help remove the sensor. Use that long breaker bar again with the O2 sensor socket.

I dont understand the different response times between the front and rear banks, that is not just a plus or minus tolerance difference. Are they the same manufacturer?

See this link its pretty interesting

http://www.napaechlin.com/Miscellaneous-02+Sensor+Tips/Content.aspx

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Both the replaced manifold sensors are AC Delco AFS 109, bought from Rockauto, so they should be the same. I am a little suspicious when it comes to those readings, though. It seems strange that the pre-cat sensor (Bank 1 Sensor 2), which is now throwing the slow-response code, would have had the same value as the fastest of the two new sensors. I am pretty sure that sensor has been on the car since new, or almost 170000 miles.

edit: spelling

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Do you have the manual? Ill have a look in my 96 manual to see if they give normal ranges for the O2 sensors and to see what your code means

I dont think we have come across the P1139 in my memory I am usually pretty good at remembering these things. I do not think that code P1139 current is cause to replace the O2 sensor. Dont jump too fast.

You may have a rich condition causing this, the plug if not firing could have caused a rich condition, how are the other plugs?, only that one is fouling? As you know, don't pull plugs and put them back in again, once a plug is pulled it must be replaced as the nickel plating on the threads to prevent seizing is disturbed.

Does your scanner have the ability to read misfire counts? If so, check all cylinders for misfire counts.

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Yep, only that one cylinder is fouling, ant it has been like that for years. I just replace that plug more often. I would fix the valve guide if it was possible without too much work, but as I understand, you have to remove and replace the whole head to do that (and also replace it with a new head, since the valve guides cannot be changed). There were no misfire codes when P1139 set. In fact, P1139 only set after I changed the fouled plug, so there should have been less problems then (btw, I always put back new plugs). When I did have some misfiring going on a few years ago, I could feel it very clearly when it happened, and the engine runs smoothly now.

I have the FSM for 97, and the code description was from there. I only scanned the descriptions very briefly yesterday (it was late), but I think that it pointed towards a faulty sensor. I will have a better look tonight. Also, P1139 does not set if P0135 (slow heater performance for sensor 1 bank 1) is active. I used to have P0135 half-often with my old sensor, but I usually cleared it to not have the light on -- I knew what the problem was anyways, so no reason to have the MIL on while driving. Not sure if it could still have prevented P1139 from setting somehow.

Thanks for staying with me on this. Although I have a FSM, I would still be happy if you wanted to look in yours too and tell me what you think. You may think of something that I would have missed.

Jonas

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I don't mean misfire codes, I mean misfire COUNTS. Can your reader provide that? Or do you mean you have checked misfire COUNTS and only see them on #5?

Long term fuel trim should be 15 to 25

Not much is said about the O2 sensor 'lean/rich' other than varies.

It is interesting that the code P1139 sets when the number of LEAN TO RICH transitions is LESS than 20 in 120 seconds or visa versa RICH TO LEAN. That would certainly suggest that the Pre-Cat O2 sensor is sluggish and therefore bad.

This code is enough to keep the system in OPEN LOOP. The failure data is stored in the FREEZE FRAM and FAILURE RECORDS, can we retrieve that?

Open Loop causes the engine to run rich and that can damage the CAT, and cause the exhaust to run hotter, damaging O2 sensors from what I understand about OPEN LOOP.

The first line of the P1139 circuit description states that the PCM provideds a 0.45 volt reference signal to the O2 sensor on CKT 1665. When the O2 sensor is cold the sensor signal voltage will be around 0.45 and the PCM will keep the system in OPEN LOOP operation. If you want check that voltage, CKT 1665 is the PPL/WHT wire.

When the O2 sensor is warm above 200 degrees C (392 F) the sensor will swing from rich to lean RAPIDLY, if the PCM is in good control of the AIR/FUEL mixture.

Given that you are fouling a plug with OIL, that sensor is probably gunked up.

My inclination is that if you have been in open loop, once you get her into CLOSED LOOP you will see a performance and fuel consumption improvement.

Read the diagnostic chart in the manual (96 manual page 6E-254) and see if your reader can provide the O2 sensor voltage and does it give you open or closed loop status?

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Yes, I meant counts. I have history counts for cyl 5 somewhere in the 500 range, and there were also maybe 10 for cyl 2 (hmmm, same coil), however, after resetting the codes and going for a drive, I still got P1139 (first) and P0138 (a little later). I then checked the current misfire counts, and they were zero for all eight cylinders (and the history counts numbers were unchanged), so there had been no misfiring during that drive, but I still got the two codes for the HO2S circuit. When the codes set this time, the MIL did not illuminate.

Yes, I can see open/closed loop. Will check.

There is an option for retrieving freeze frame data in ScanXL, the program I use, however, when I try it, it seems to scan several hundreds of PID:s (data values from the PCM) at the time of the scan, and not what was stored earlier. How much data should be in the freeze frame?

The two sensors from the manifolds looked very similar (see the picture in one of my earlier posts), so I think that the oil issue of cyl 5 does not propagate to the O2 sensors (or the one in the rear manifold should have looked worse than the on in the front manifold). Maybe the oil has time to burn before going into the exhaust.

I do not think that I can see the O2 sensor voltage with my reader.

I wonder why I get P1139 Insufficient Switching and not P0139 Slow Response. A sluggish sensor should set the latter one (which I do not get), but then both of them have the same descriptions, that they are designed to set if the O2 sensor is slow to respond.

I do have one major concern: is there any chance at all that something got damaged when I tried to start the car with the battery drained and then jump starting? I don't think that should hurt anything, but it did precede the problems. Is it normal that the displays flicker and the radio produces static noises while trying to start with a very drained battery (when that happened, I let go of the key, and the flickering and crackling sounds stopped).

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You have mentioned this a couple of times about jumping the car with a dead battery, I dont think you caused any problems as long as the cables were not accidently swapped positive to negative.

I will read your post above later, I am running out of the house for a bit

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I was a bit worried because of the flickering, but the cables were correctly connected (no swap positive to negative), so there should not have been any problems. My working theory at the moment is that when all sensors were old, everything was a little slow, and the pre-CAT sensor could keep up with the rest of the system. Now, when the main regulating sensors are fast (the ones in the exhaust manifold), the one in front of the oxygen sensor can no longer keep up. I do not know if that makes sense, because I do not know in enough detail how the feedback loop works -- for example, if the PCM will switch between enrichment/leaning faster when the manifold sensors are new.

edit: typo

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I extracted the freeze frame data with a different program (same OBD II interface). OBDwiz worked, where the ScanXL did not (although the latter is supposed to be more powerful, and can extract more PID:s).

Below is the freeze frame data:

PID Description Value Units

0x02 Freeze frame DTC P0138

0x03 Fuel system status Closed-loop, using oxygen sensor feedback to determine fuel mix

0x04 Calculated load value 12.55 %

0x05 Engine coolant temperature 194 F

0x06 Short term fuel % trim - Bank 1 3.12 %

0x07 Long term fuel % trim - Bank 1 28.91 %

0x08 Short term fuel % trim - Bank 2 3.12 %

0x09 Long term fuel % trim - Bank 2 14.06 %

0x0B Intake manifold absolute pressure 9.86 PSI

0x0C Engine RPM 1646 RPM

0x0D Vehicle speed 5.92 MPH

0x10 Mass air flow rate 3.79 lb/min

0x11 Absolute throttle position 9.8 %

I also discovered that I can see oxygen sensor voltages. The two in the manifolds changed erratically on the screen, which is to be expected if they swing back and forth and the sampling rate of the scanner is too low to resolve those swings. In other words, they looked OK. The pre-CAT sensor stayed mostly around 0.6-0.7 V, which is too high. I think the average should be about 0.4, and then it should also swing back and forth. I did, however, see it swing down to as low as 0.12 V occasionally, but it mostly stayed high. The post-CAT sensor stayed high like it should, although it sometimes dropped after the pre-CAT sensor dropped. Those drops could be several seconds long, indicating that the engine was running lean for a while (I think that a faulty CAT should result in fluctuations on a much shorter time-scale, and 10 seconds would probably be enough to saturate/deplete even a new CAT with/of oxygen).

edit: formatted the table for readability.

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The long term fuel trim is something to look into Bank 1 is 28.91 and Bank 2 is 14.06. Where as the short term on both is 3.12. What do you think the long term difference is related to?

You are also getting this code correct? >>> P0138 - Heated Oxygen Sensor (HO2S) Circuit High Voltage Bank 1 Sensor 2, that is the pre-cat

Bank 1 Sensor 1 - right bank (rear) manifold

Bank 1 Sensor 2 - pre-cat

Bank 1 Sensor 3 - aft-cat

Bank 2 Sensor 1 - left bank (front) manifold

It certainly looks like your pre cat O2 sensor is suspect. But what causes High Voltage, that is indicated by the code and by your snapshot...

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When I look at the long-term fuel trim during a test drive today, I can see that it started out at 3.1 for bank 1 and 4.7 for bank 2. Then, after a short while, it started to change a lot. Below are values for short and long term fuel trim for both banks, extracted during a short time of my test drive. The data is organized as a time stamp (in ms) followed by a value. There is about 3 seconds between each row (a bunch of other parameters were recorded in between).

edit: the values come from a portion of driving at approximately 55 mph, but the engine load was varying between 50 and 100 Nm (68 - 136 ft-lbs), so it was not steady-state.

Time	Sh 1	Time	Lo 1	Time	Sh 2	Time	Lo 2
1560187  -2.3   1560234   3.1   1560281  -9.4   1560328   4.7
1563546  -1.6   1563593  20.3   1563640  -7	 1563687  12.5
1566765  10.2   1566828  20.3   1566875   2.3   1566921  12.5
1570093  -6.3   1570125  20.3   1570171  -6.3   1570218  12.5
1573312 -12.5   1573359   1.6   1573406  -9.4   1573437   4.7
1576671  -7	 1576703   3.1   1576734  -8.6   1576765   4.7
1576671  -7	 1576703   3.1   1576734  -8.6   1576765   4.7
1580156  -0.8   1580187   3.1   1580218  -6.3   1580250   4.7
1583671   3.1   1583718   5.5   1583765  -6.3   1583812   4.7
1587078   3.9   1587125  18	 1587171  -0.8   1587218  12.5
1590500 -10.9   1590546   4.7   1590593 -13.3   1590640   3.1
1593765 -10.9   1593828   1.6   1593875 -10.9   1593921   2.3
1597109  -4.7   1597156   5.5   1597203  -4.7   1597250   3.9
1600437   8.6   1600484  25.8   1600531   7	 1600578  13.3
1603937   0	 1603984  25.8   1604031   1.6   1604078  13.3
1607406   2.3   1607453  21.1   1607500  -1.6   1607531  10.2
1610734 -10.9   1610781   2.3   1610828 -12.5   1610875   1.6
1610734 -10.9   1610781   2.3   1610828 -12.5   1610875   1.6
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  1. Bank 1 keeps reverting to the 20's while bank 2 is reverting back to 12 to 13. I wonder why. Maybe members familiar with this will comment. I need to look the manual over when I get a chance, but I am running in an out right now

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