02 Sensor Issues - MAF, Sensors, What else?

[TheEnder53]

Hello all.

I’ve had some confusing issues with my Tahoe since I bought it stemming from the 02 sensors.

Originally, when it was colder out, I would get a repeated P0157 only if i beat on it. Had to be at or near wide open throttle for it to set. I was able to get it smogged here in California.

Now, it sets all the time, even when i’m not beating on it. It takes a few miles, but it will always set.

Today, after coming to a stop, i realized it had literally no power at all and would rev all the way up to 3-4K with light throttle and then shift very fast (like it had a shift kit) and struggled to hit 55 on flat land. Checked codes, had a code set for P0131.

Cleared it, hasn’t come back since. P0157 is there still however. The B2S2 02 Sensor is new (replaced in March) from Autozone and reads 0V at all times according to my scanner.

Unrelated, or possibly related, today was a very hot day. Around 115°F here where I live. Stopped in traffic because of an accident with my phone hooked up to it the engine was hovering around 225-228°F, which in my mind is overheating. It cooled down if I put it in neutral and revved it to around 1500 RPM. A/C was also blowing maybe 10° colder at best. Sounded like a jet engine once traffic cleared though and it returned to normal temps.

Reading around i’ve heard a few people say it could be maf, or something else. Where do I start?

 

[OR VietVet]

To me, with both codes, sounds like you have a clogged catalytic converter and an emission problem causing it. Before we get deeper, can you share the year and engine size of what you are driving? Mileage? Is it a secret? Not all GMT800 vehicles have exactly the same powertrains in them.

 

[strutaeng]

...multiple issues going on. :-(

Low voltage means lean, right? That may be your issue, it's running lean. Somehow not throwing a lean code like P0171/0174?

Overheating? Not sure, that needs it's own diagnosis by itself. Clogged catalytic converters is very possible. Running a vehicle with misfire for extended amount of time can damage the cats. Did that ever happen to you? Or give us the background on the truck. Are you the original owner, only driven to Church on Sundays? You just bought the truck and are racer car driver on training wheels? We have no idea?

Revving and not going anywhere? Transmission slipping? That needs diagnosis by itself too.

This can get expensive by the DIY throwing parts at it. Probably best to find a local trustworthy mechanic or shop nearby.

 

[TheEnder53]

To me, with both codes, sounds like you have a clogged catalytic converter and an emission problem causing it. Before we get deeper, can you share the year and engine size of what you are driving? Mileage? Is it a secret? Not all GMT800 vehicles have exactly the same powertrains in them.

Yes. 2001 Tahoe LS 5.3 4X4. Has just a hair under 250,000mi on the odometer.

 

[TheEnder53]

...multiple issues going on. :-(

Low voltage means lean, right? That may be your issue, it's running lean. Somehow not throwing a lean code like P0171/0174?

Overheating? Not sure, that needs it's own diagnosis by itself. Clogged catalytic converters is very possible. Running a vehicle with misfire for extended amount of time can damage the cats. Did that ever happen to you? Or give us the background on the truck. Are you the original owner, only driven to Church on Sundays? You just bought the truck and are racer car driver on training wheels? We have no idea?

Revving and not going anywhere? Transmission slipping? That needs diagnosis by itself too.

This can get expensive by the DIY throwing parts at it. Probably best to find a local trustworthy mechanic or shop nearby.

No lean codes at all. Just the P0157 and now the P0131 that hasn’t come back yet.

It hasn’t misfired at all, and without the P0131 setting it drives just fine with no power loss at all. It’s only when that code specifically sets to where it loses all power. I don’t believe the transmission is slipping as it engages all gears without issue.

I’m the 3rd owner from what I can tell on the carfax. No clue how it was driven other than the fact that the engine (from looking at it through the oil filler with a camera) was very clean. I will attach a picture below. I drive pretty moderately. Apologies for not including more, just been a wild day.

 

[Donal]

If you prefer to replace parts to trouble shooting, do this. Replace air filter, catalytic converter, fuel pump, fuel filter, all O2 sensors, thermostat, water pump, radiator and antifreeze.

 

[2006Tahoe2WD]

"Just the P0157". I Googled "P0157 Chevy" This is what comes back.

P0157 stands for “Oxygen Sensor Circuit Low Voltage (Bank 2, Sensor 2).” This code is triggered when the powertrain control module (PCM) detects a problem with the downstream oxygen sensor. A damaged oxygen sensor, exhaust leaks, and a lean running condition are possible reasons why this trouble code is set.

 

[rockola1971]

Its 115deg where OP is? He live in death valley? As soon as that 2001 Tahoe leaves the driveway every morning it is singing the "I think I can, I think can" melody. Good Gawd 115deg! You live in an oven along with your Tahoe bro!

P0131 B1S1 ---Upstream of Cat 02 This is one of the 02's that controls your fuel injection
P0157 B2S2 ---Downstream of cat 02 This is one the 02's that monitors your Cat for performance and that is all. Has nothing to do with control of your fuel injection. It is simply a emissions warning sensor.

You need live data during the poor running event to see what your fuel trims and o2's are saying is going on. But a quick in dirty is get underneath to verify all wiring from o2's are intact and not rubbed up against ground or melted up against something metal also verify wiring harness for ignition coils on that bank as well. Could have an injector on B1 hanging open randomly.

The PCM with its code is pointing you where to start looking by telling you the bank that is having problems. Wouldnt pay too much attention to the B2S2 right now UNLESS you take IR thermometer ($30 amazon, ebay, harbor freight) of the inlet and outlet of B2 Cat. If your Cat outlet is substantially lower in temp than the inlet then Cat is plugged up. While you are under there and engine running go ahead measure both Cats.

My man dont need no grill. He just slaps steaks on his porch concrete until done to likeness.

 

[TheEnder53]

Its 115deg where OP is? He live in death valley? As soon as that 2001 Tahoe leaves the driveway every morning it is singing the "I think I can, I think can" melody. Good Gawd 115deg! You live in an oven along with your Tahoe bro!

P0131 B1S1 ---Upstream of Cat 02 This is one of the 02's that controls your fuel injection
P0157 B2S2 ---Downstream of cat 02 This is one the 02's that monitors your Cat for performance and that is all. Has nothing to do with control of your fuel injection. It is simply a emissions warning sensor.

You need live data during the poor running event to see what your fuel trims and o2's are saying is going on. But a quick in dirty is get underneath to verify all wiring from o2's are intact and not rubbed up against ground or melted up against something metal also verify wiring harness for ignition coils on that bank as well. Could have an injector on B1 hanging open randomly.

The PCM with its code is pointing you where to start looking by telling you the bank that is having problems. Wouldnt pay too much attention to the B2S2 right now UNLESS you take IR thermometer ($30 amazon, ebay, harbor freight) of the inlet and outlet of B2 Cat. If your Cat outlet is substantially lower in temp than the inlet then Cat is plugged up. While you are under there and engine running go ahead measure both Cats.

My man dont need no grill. He just slaps steaks on his porch concrete until done to likeness.

Apologies for not responding sooner. Been a bit rough here, that and the fact I got a new phone and didn’t know how to log in for a bit. lol.

I can confirm at least according to data PIDs it’s running lean. It’s adding around +25% fuel trims on long terms and short terms for both banks. Yet doesn’t have a code for running lean, but the P0157. It was also retarding to spark according to HP tuners due to spark knock.

It’s been a while, and it still hasn’t set a P0131 again. And yes, where i was was quite close to death valley, lol. It was hell in the heat wave we recently had here.

Only thing to note, i’m not sure if the fuel filter has EVER been replaced in this. Same with the regulator valve. Everything under the hood appears to be completely original. I’m debating switching to e-fans as the clutch just cannot cool it down in temps this high.

It also is now starting to have a hard time starting occasionally. It’ll crank for a few seconds, catch a little bit, then crank for a few seconds again, then finally fire up.

 

[rockola1971]

Apologies for not responding sooner. Been a bit rough here, that and the fact I got a new phone and didn’t know how to log in for a bit. lol.

I can confirm at least according to data PIDs it’s running lean. It’s adding around +25% fuel trims on long terms and short terms for both banks. Yet doesn’t have a code for running lean, but the P0157. It was also retarding to spark according to HP tuners due to spark knock.

It’s been a while, and it still hasn’t set a P0131 again. And yes, where i was was quite close to death valley, lol. It was hell in the heat wave we recently had here.

Only thing to note, i’m not sure if the fuel filter has EVER been replaced in this. Same with the regulator valve. Everything under the hood appears to be completely original. I’m debating switching to e-fans as the clutch just cannot cool it down in temps this high.

It also is now starting to have a hard time starting occasionally. It’ll crank for a few seconds, catch a little bit, then crank for a few seconds again, then finally fire up.

Id replace that fuel filter immediately. It could be your cause of fuel starvation. The hard starts could be your fuel filter or your fuel pump is getting ready to die. But being that you are in a oven, that could just be vapor lock. Fuel regulator is cheap and easy to replace, but i can be checked for a torn diaphragm.

 

[nonickatall]

So I would start logically.

The fuel system works as follows.

You accelerate and the throttle opens.

The engine sucks in more air and therefor oxygen, this is measured by the MAF. Based on this measured value, the engine control calculates the corresponding injection quantity with the help of other parameters, e.g. the engine temperature.

The point of the whole thing is to inject so much fuel, that all fuel molecules can react with all oxygen molecules and produce optimal combustion.

But since this is never really possible because, for example, the amount of oxygen at sea level is greater than in the mountains and on a dry winter day it is greater than on a humid summer day, the o2 sensors measures the residual oxygen content in the exhaust gas.

Based on this values, the motor control adjusts and tries to reach lamda 1. In order for this system to function, it is essential that the intake line between the cylinders and the MAF is airtight.

For example, if your vehicle is drawing incorrect air, the MAF measures less air than actually reaches the engine.

Therefore, the very first step is to check whether you have a false air problem. It only makes sense to check this with a smoke test.

A false air problem can arise, among other things, from a defective intake area between the throttle valve and MAF, but also from a leaky oil cap or even an oil dipstick seal, but also from the intake manifold seals or a defective evap system. The hose between the PCV and the intake manifold may also be defective.

If it's not a false air problem, it could be a sensor problem and of course the MAF, the o2 sensors and the temperature sensor are suspect.

Since your engine doesn't show that it is much too hot or much too cold, the sensor for the coolant temperature gauge and the ecm are the same, and the o2 sensors have been changed, then of course the MAF remains.

Of course, it can also be the case that the amount of fuel injected is not correct because, for example, the fuel pressure is too low.

Since it mainly happens at full throttle, this can also be a cause if, for example, the fuel filter is tight and too little fuel reaches the engine at full throttle, which can also lead to the engine running too lean.

Not all of our vehicles were equipped with a fuel filter. I don't know what it's like with yours. You can measure the fuel pressure with a pressure gauge. In order to be able to measure this properly at full throttle, you would have to place a pressure gauge so, that you can observe it through the windshield when you accelerate at full throttle.

Fazit:
First do a smoke test., them check fuel pressure also at full throttle, while driving, clean MAF, if all does not help, swap MAF.

A defective cat has other symptoms...