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When I left the private sector cars had 1 O2 sensor, except for the very few that had dual exhaust. Never heard of fuel trims back then. Jump to today, I have some drivability issues and a CEL. I am working on a 05 GMC Yukon XL Denali wit a 6.0L. I am getting P0171B, Fuel Trim Lean Bank 1, & P1133B HO2 Sensor insufficient Switching B1S1.
Along with this, I have rough idle and misfires ONLY after driving for a while & turning off the engine, ( stopping for gas, pick stuff up at the store, etc.) & starting down the road again and hitting a stop light is when the rough idle happens. Seems to clear itself after 5-10 mile of continuous driving.
This week it has started bog down when accelerating from a stop. I can release the gas pedal and tap it to get it going.
I have access to a really good scan tool. What I am seeing is 3 of the 4 O2 sensors working as they should, (or 3 of the 4 are bad). B1S1 stays around 350mv. The other 3 are around 35mv. STFT & LTFT stay at “0”. Engine stays in open loop.
Any help will be greatly appreciated.
First thing I would do is induce lean and rich conditions to see if the O2 sensors respond appropriately.
If your still in open loop with engine at full operating temp… the O2 sensor heater circuit is not functioning correctly (P1133). You cannot have 0 STFT and LTFT with a PO171. A PO171 is a lean condition, your trims will be positive as system is adding fuel to compensate for extra air. Because of this I would check for proper signals to the O2 sensors. Rough idle when warm would indicate an intake manifold gasket leak. When cold idle is Ok because gasket seals itself but as engine gets hot, the intake manifold and head expand causing the gasket to leak. Don’t work on the gasket leak yet, get the O2’s in closed loop and reporting trims first. O2 signal will oscillate high and low in a wave pattern if working properly. Sounds like a wiring problem.
Thanks for the help. I wish my scan tool would let me share the recordings. It would be a lot easier. Plus, it has bee 30 years since I had any training or real challenges in diagnostics.
I agree, the driveability issues can be tackled after the fuel trims/O2 sensors/open loop issue.
I will not be able to get back into working on this until the weekend, but I can add/update some things now. I recorded the data stream as I was driving home one day. All the fuel trims stayed at “0”. B1S1 was fluctuating, around 350mv average. B1S2, B2S1 and B2S2 were also fluctuating, averaging around 35mv. The readings for the heater circuits were as follows; Both banks, S1 showing .76A. B1S2 was .52A. B2S2 was .46A. I am guessing the O2 fuses are good, otherwise I should see 0A on the heater circuits.
I have readings for MAF, MAP, RPM, speed, etc. One thing I did notice in a snapshot of the readings was the accelerator pedal position indicated angle, 0% and the throttle position indicated angle, 28%. Again, this was a snapshot. Might mean nothing, might mean a lot, I just do not know.
Thanks again for the help. This is definitely an OJT/learn as I go experience for me.
We recently purchased an OTC Evolve. Still learning it. Has built in wiring diagrams, specs, etc. We also have the trial of identifix.
you have access to real time data then… working with the P0171/P1133 codes, you are looking at a problem with the bank 1 02 sensor, most likely the heater circuit.
You have several 02 sensors, but only focus on B1S1 and B2S1 02 data for now. The two sensors are the upstream sensors located just below the exhaust manifold in the head pipe on each side of a V engine. The P0171 code is the B1S1 and P0174 is the B2S1. Bank 1 on GM is the driver side.
Using live data, select a graph mode for the B1S1 and B2S1 STFT and LTFT as well as the voltage for both. On start up your 02 voltage will be high then quickly drop as the heater circuit brings the 02’s into operating/closed condition. Once in close loop, the 02 voltage will oscillate between 150 and 800mv… if they do not drop in voltage or remain high that indicates a problem with that 02 or its wiring. Your STFT and LTFT should show a high (above +10) reading for the B1S1 02. This indicates the lean condition and a P0171 code. A defective heater in the 02 will not allow the 02 to operate correctly and give the P1133 and P0171 codes. Swap the B1S1 and B2S1 02’s and see if you now get a P0172 code. Don’t forget to clear all codes before restarting.
Coolant temp is important. The engine needs to be at correct operating temp. You reported that the STFT and LTFT are always at 0. Either your not reading the data correctly or the engine temp is low which will cause the system to remain in closed loop.
You have a very good scanner and I do not have any expertise in that device, so I could confuse you with attempting to use the scanner for anything more that the basics for now.
If the problem moves to the bank 2 sensor after swapping, I would change the 02. I say this because of the P1133 code. If it was just a P0171 I would do more testing. Remember, the reason for this site is to NOT be a parts changer.
jkreutzer, thank you very much. I guess my diagnostic skills have deteriorated to the point that simple things just do not come to mind. Never occurred to me to swap the O2 sensors and see if the problem moved.
I added a link to a couple of screen shots of the data stream I recorded. Looking at the parameters, this thing should be in closed loop.
“https://drive.google.com/open?id=1fECFrjMd3i9qziLE4nIPrJaKfz4QxwX3”
In case the like does not work, the coolant temp sensor is showing 192deg. I was doing 58mph with engine speed of 1678rpm. When I replay the recording the O2 sensors do fluctuate.
The car is back at the dealer for some other repairs they promised to do. They are “supposed” to take care of the CEL as well. We will see. I will post the fix, when it happens.
I agree about the reason for this site. It would be a lot easier to throw $1500 in sensors,injectors, converters and gaskets. But, I do not like to work that way. Especially when a little extra work leads to a $50 part.
Thanks again for your guidance. You sound like a good teacher.
Credit goes to Matt of Schrodinger’s Box and Paul Danner of ScannerDanner. They are the real teachers. Thanks Matt and Paul.
OK, I got the car back from the dealer. They replaced B1S1. This was the odd one that reading way different then the other three. I did not have the opportunity to speak with the tech. I do not know if he checked anything else or just guessed. The CEL is off. I hook up the Evolve for the ride home this evening. Now goes into closed loop. Fuel trims and O2 sensors are reading normally.This also took care if the misfire after a hot start.
The only thing left is the intermittent hesitation when accelerating slowly from a stop. Narrowed this down to NOT a engine problem. Seems like the traction control/ABS has a mind of its own. I had a yellow ABS light and a red brake warning light, a traction control fail light and a couple of warning in the DIC. Dealer had stated when they see this the problem is the ABS controller. They paid for a used controller the I installed. Seemed to work for about a week. Then started getting the “traction active” in the DIC. No warning lights.
So, now I get to learn how to use a new scanner to diagnose a vehicle system that did not exist when I was in dealerships and now nothing about. The fun never ends.
Thanks to everyone for the help with the drive-ability problem.
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