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//Negative Camber\\
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1,050 Posts
Discussion Starter #1
Whats up?

To start off I have a 1997 GMC C1500 with a 5.7 in it.

So my check engine light is on and my truck is running like dog poo right now. I got me a scanner to get the code and had 2 codes.

P0175 System to rich Bank 2
p0137 O2 Circuit low voltage (bank1 sensor 2)

So I have a couple of questions.

1. Which side is bank 1 and which is bank 2?
2. Is sensor 2 the one after the cat?
3. I found that the low voltage means that the sensor is reading lean so is it possible that that sensor is reading lean then the computer is adding fuel which caused the other side then to read rich?

Thanks,
Chad
 

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HOT AIR BALLOON OWNER
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14,932 Posts
First, mileage? Ever swapped front O2 sensors on it before?

If you are around 60-100k and never done them, pucker up your butthole and go buy two new fronts. They get tired and weak with age. You can run universals if you have the time to solder them in, work fine. I did, saved $200 on a LS400 recently.

I could swear Bank 2 is Driver side. Sensor 2 issues are rarely anything, they are generally upstream issues, AT TIMES it is the converters that are bad.
 

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//Negative Camber\\
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Discussion Starter #3
they were changed about 60K ago. I have new cats on there so they aren't bad. I figure I will change them as they start going bad cause I can't afford to replace them all at once. Is sensor 2 the after cat o2 sensor?

Thanks,
Chad
 

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Resident Guinea Wop
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14,533 Posts
Bank 1 = Cylinder 1/Drivers Side

Bank 1 Sensor 1 = Upstream (before cat) Drivers Side
Bank 1 Sensor 2 = Downstream (after cat) Drivers Side
Bank 2 Sensor 1 = Upstream (before cat) Pass Side
Bank 2 Sensor 2 = Downstream (after cat) Pass Side

Commonly referred to as 1/1, 1/2, 2/1 and 2/2

I just went through this on my truck, had a P0135 HO2S Circuit Malfunction :rofl2:
 

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//Negative Camber\\
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1,050 Posts
Discussion Starter #5
Where do I go from here? Do I just replace the sensor with low voltage and see what that gets me? I have read some responses on here about each of these codes independently, but I haven't really seen anything with both of them and that is what is confusing me. One side is saying rich and the other is saying lean.

Thanks,
Chad
 

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GMFS Uber-Member
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688 Posts
If you have a DSO like a Fluke 98 it would be best, but a standard multimeter like a Fluke 87 or your average Craftsman can help you figure out if it is the O2. Just hook up the red lead on your multimeter to the signal wire on the O2 and the black lead to ground, preferably on the chassis and not on the sensor. With a multimeter, just put it in the average mode, I think it's a key toward the top that says AVG for min/max/avg. If you test it and your avg is lower that 450mV then it's your sensor. But check all your sensors, cus one showing lean (low voltage) can throw them all off.
Hope this helps.
 

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//Negative Camber\\
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Discussion Starter #7
That does help. I don't have a multimeter, but i think one of my buddies does.

Thanks,
Chad
 

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HOT AIR BALLOON OWNER
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14,932 Posts
Don't replace the rears. Start with the lazy one and see what happens.

Do you have a way to log the truck and see how many mV the sensors are putting out?
 

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//Negative Camber\\
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Discussion Starter #9
Don't replace the rears. Start with the lazy one and see what happens.

Do you have a way to log the truck and see how many mV the sensors are putting out?
Well, the lazy one is a rear one. Should I still just try the front ones?

And I don't have a way to check the mV.

Thanks,
Chad
 

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HOT AIR BALLOON OWNER
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Rears are only cat efficiency sensors. I'd just get some O2 Sims to get them turned off.
 

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//Negative Camber\\
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Discussion Starter #11
So even though the rear o2 sensor is throwing the code I should replace the front one on the same bank?
 

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HOT AIR BALLOON OWNER
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So even though the rear o2 sensor is throwing the code I should replace the front one on the same bank?


Rears do not go bad, they are not for reading A/F for the motor.

I'd swap both fronts.
 
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