Just got these errors. Recently replaced the O2 sensors on the driver side and fixed the exhaust leaks with new gaskets. But now seeing these. Is this an O2 sensors or something else?

 

Seems both those codes could be caused by a vacuum leak (among other things). Maybe the new sensors uncovered a pre-existing problem.

What are your long and short term fuel trims? Can you view real time O2 sensor voltages for both banks, pre-cat?

obd-codes.com has lists of possible causes

 

Thanks John. I did some trending for the O2 sensors for my recent commute. Here is the data. First trend is bank 1 and the second is bank 2.

 

that bank 1 sensor in red looks low if it is the rear

 

Bank1 Sensor 1 is the front - correct? It was like that last year and I replaced it because I thought it was low. It hasn’t changed even though it replaced it.

 

Can you read the long term fuel trims (LTFT) for both banks? If up in the 25% area (maximum limit) for bank 1, then you might have a vacuum leak or low fuel pressure/flow problem. Long term fuel trims less than 5% are normal for good running engines, according to my mechanic.

Bank 2 looks normal. Good modulation of the blue trend. So, how could a vacuum leak or fuel delivery problem effect only one bank? Maybe try swapping the pre-cat sensors to see if the problem swaps. That will prove the new sensor.

Having said that, there are a couple things that are confusing. Bank 1 shows lean (too much air, low voltage) pre-cat (B1S1 red trend), but rich post-cat (B2S2 green trend) for most of the time. Then there are a couple events at the beginning that show B1S1 rich pre-cat (was that idle at a stop sign?) If it was at idle (maximum plenum vacuum), that can be a clue. It also looks like there are intermittent periods where both sensors read zero on both banks (that's not normal), maybe an open circuit or ECU fault (hope not). Maybe it's something to do with your scanner. If you can, watch short term fuel trims as you drive, along with the O2 signals. STFT at idle vs under load can clue us in to the nature of the problem.

I spent a lot of time chasing O2 sensors on my 96 4.0 D1. Lot's of plugging and unplugging and swapping and such. Finally got it all together and was able to identify some serious engine vacuum leaks. Now it runs great. Hopefully we'll get yours straightened out too!

 

Thanks John - I appreciate the analysis and help. Here are my STFTs from the same trip. I will keep an eye on them on my way home. I will also check for any obvious hose or vaccum leaks. LTFT for bank 1 was 21.88, For bank 2 it was 1.56.

 

^^^^ Excellent assessment in my opinion (referencing JohnZo's post). The bank 2 graph is ideal and Bank 1's looks suspect (referencing the initial O2 graphs posted). Swapping sensors (assuming they've been out in this decade) is a simple way to see if this is a sensor problem or an actual engine condition. Here's a chart of mine for comparison, I believe we're both using OBDFusion. Mine are grouped differently, I did the fronts as they compared to the rears so it's not exactly the same graph however the behavior is the important part, the constant cycling (aka dithering) over the full voltage range. Just to say it, the fronts are used to trim the fuel maps and the rears simply alert the ECU that the cats are no longer doing their job. I have a handful of spare BOSCH ECUs from 03s and 04s if you're looking to troubleshoot.

 

Fantastic info Ahab. I may take you up on that. I will swap the front sensors tomorrow morning and see if I can rule out a bad sensor. Just replaced this with a walker a couple of months ago because the old one had frayed wires. Will post when I get new info.

 

OK. Now we're getting somewhere.

LTFT way up on Bank 1 means ECU is trying to add fuel, because the O2 signal says Lean.

So, if it really is lean, we have air leaking into that bank, or low fuel flow (e.g. a weak injector or other blockage could do this). Or, it's not really lean but the O2 sensor is sending a low voltage signal. The swap will tell us which option is true.