Need help - 01 Tahoe 02 Sensor Woes

[TheSavage4.7]

Hello all.

I’ve had some confusing issues with my 2001 Tahoe 5.3 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?

 

[ctechbob]

Isn't that the vintage of GM where the MAF misreporting can cause all kinds of problems, up to and including a burned up trans?

@clinebarger probably knows, he's the resident expert on that kind of stuff.

 

[TheSavage4.7]

Isn't that the vintage of GM where the MAF misreporting can cause all kinds of problems, up to and including a burned up trans?

@clinebarger probably knows, he's the resident expert on that kind of stuff.

Yes unfortunately.

When it works, and it worked without setting the P0131 the entire way home, the trans didn’t shift nearly as fast either. Back to its sort of sluggish shifts.

 

[clinebarger]

A underreporting MAF would affect both banks.

I would need to know is it has Delco or Denso O2 sensors to give good diagnostic info, Delco would have flat connectors & Denso uses square.

Hopefully it's just a dying upstream bank 1 sensor.

 

[TheSavage4.7]

A underreporting MAF would affect both banks.

I would need to know is it has Delco or Denso O2 sensors to give good diagnostic info, Delco would have flat connectors & Denso uses square.

Hopefully it's just a dying upstream bank 1 sensor.

That would be a denso then from what i recall replacing the B2S2 sensor.

 

[Rhymingmechanic]

The temperature event is probably unrelated. It's very similar to something that happened to my '01 Silverado in a school pickup line a couple times. The jet noise was the fan clutch finally locking up when it got hot enough.

If you've never done it, a new (OEM) fan clutch could be worthwhile, especially if your A/C is consistently weak at idle.

 

[TheSavage4.7]

The temperature event is probably unrelated. It's very similar to something that happened to my '01 Silverado in a school pickup line a couple times. The jet noise was the fan clutch finally locking up when it got hot enough.

If you've never done it, a new (OEM) fan clutch could be worthwhile, especially if your A/C is consistently weak at idle.

Yeah, I’m considering the new fan clutch. It’s a very old SUV with a lot of miles.

That should help out a ton i would think.

 

[clinebarger]

Do you have a way to monitor O2 voltage via a scan tool?

*On a normally functioning sensor, Engine cold, Key on, Engine off....Voltage will start out near 500 mV or 1/2 a Volt. Low as 450 mV is considered normal. This is the Bias Voltage supplied by the PCM.
Removing the O2A fuse is helpful to prevent the heater from skewing the voltage during this test.

*If Bank 1 Sensor 1 voltage is a lot different than Bank 2 Sensor 1.....Unplug B1S1, If the voltage is now at Bias Voltage, Replace the sensor.

It can be tough to see the switch rate without graphing the voltage via a capable scan tool or lap scope, If the above test using Bias Voltage doesn't produce results.....Comparing B1S1 & B2S1 switch rate can be helpful, If B1S1 gets lazy & sticks low intermittently it can cause a P0131.
*The HO2S voltage is less than 200 mV for 165 seconds is the set criteria for P0131.



Harness pinout for B1S1 if needed.....
Pin A, Tan wire is the Low Reference.....Ground supplied by the PCM.
Pin B, Purple/White is the Signal Circuit to the PCM.
Pin C, Pink wire is the Ignition Hot for the heater.
Pin D, Black wire is the case ground for the heater.

 

[TheSavage4.7]

Do you have a way to monitor O2 voltage via a scan tool?

*On a normally functioning sensor, Engine cold, Key on, Engine off....Voltage will start out near 500 mV or 1/2 a Volt. Low as 450 mV is considered normal. This is the Bias Voltage supplied by the PCM.
Removing the O2A fuse is helpful to prevent the heater from skewing the voltage during this test.

*If Bank 1 Sensor 1 voltage is a lot different than Bank 2 Sensor 1.....Unplug B1S1, If the voltage is now at Bias Voltage, Replace the sensor.

It can be tough to see the switch rate without graphing the voltage via a capable scan tool or lap scope, If the above test using Bias Voltage doesn't produce results.....Comparing B1S1 & B2S1 switch rate can be helpful, If B1S1 gets lazy & sticks low intermittently it can cause a P0131.
*The HO2S voltage is less than 200 mV for 165 seconds is the set criteria for P0131.



Harness pinout for B1S1 if needed.....
Pin A, Tan wire is the Low Reference.....Ground supplied by the PCM.
Pin B, Purple/White is the Signal Circuit to the PCM.
Pin C, Pink wire is the Ignition Hot for the heater.
Pin D, Black wire is the case ground for the heater.

I have both HP Tuners and Torque Pro.

Both B1S1 and B2S2 appear at the same voltage. Only issue key on engine off cold is with B2S2. It reads 0 at all times with no changes at all. Cold or hot.

 

[TheSavage4.7]

B1S1 and B2S1 both start out at around 500mv too.

 

[clinebarger]

Another test is to leave the key on , engine off & let the heaters warm the sensors, The voltage on both upstream sensors should drop voltage together & evenly.

Far as the B2S2/P0157......Unplug the sensor & see if the voltage jumps to Bias Voltage.

 

[TheSavage4.7]

Another test is to leave the key on , engine off & let the heaters warm the sensors, The voltage on both upstream sensors should drop voltage together & evenly.

Far as the B2S2/P0157......Unplug the sensor & see if the voltage jumps to Bias Voltage.

I’ve been told I don’t really have to worry about the P0157 and that’s it’s really only there for emissions. So that’ll come last.

As for the other test you were talking about, i will do it now.

 

[TheSavage4.7]

Another test is to leave the key on , engine off & let the heaters warm the sensors, The voltage on both upstream sensors should drop voltage together & evenly.

Far as the B2S2/P0157......Unplug the sensor & see if the voltage jumps to Bias Voltage.

Interesting thing that’s happening here.

According to torque pro, B1S1 drops to around 0.1V within around a minute. B1S2 is still at 0.3V,
B2S1 is stuck at 0.3V, and B2S2 dropped to 0.1V almost immediately.

Hmm, wonder if the new 02 sensor i dropped in for B2S2 was bad. And maybe the rest are dying too.

 

[clinebarger]

Interesting thing that’s happening here.

According to torque pro, B1S1 drops to around 0.1V within around a minute. B1S2 is still at 0.3V,
B2S1 is stuck at 0.3V, and B2S2 dropped to 0.1V almost immediately.

Hmm, wonder if the new 02 sensor i dropped in for B2S2 was bad. And maybe the rest are dying too.

I would replace B1S1. Unplug B2S2 just to make sure it rebounds to Bias Voltage.

I buy Denso sensors from either Autozone or Summit Racing, Both are Denso dealers......Summit Racing is also a AC-Delco & Chevrolet Performance parts dealer

 

[BrendanC]

check grounds on body mounts and replace the O2 sensors with either Denso or ACDELCO parts. no aftermarket electrical stuff on GM’s.

 

[TheSavage4.7]

check grounds on body mounts and replace the O2 sensors with either Denso or ACDELCO parts. no aftermarket electrical stuff on GM’s.

Yeah, I know they weren’t OEM sensors from GM.

I will replace with OEM and hopefully it fixes it.