98-99 Suburban C1500 2wd O2 sensors location?

98/99 C1500 Suburban 2wd R engine code 5.7 liter, leather seats :grinyes:

Just replaced the infamous intake manifold gaskets (again) and flushed out the engine best I could. Drove about 25 miles, no problem, runs smooth and seems powerful. Filled her up with gas, came home, parked. Later went out to start, will not start. Cranks but no start. SES light is now on.

Check code: "P0160 O2 Circuit No Activity Detected (Bank 2, Sensor 2)"


I've looked under the truck. I see 02 sensor on Driver's side mid-way up the exhaust pipe like a foot down from left manifold
I see O2 sensor behind catalytic converter (cc)
I see another in front of cc on pass side. Thats three. Where's the forth located?

1st question: WHERE IS LOCATION OF THIS SENSOR?


I wiggled connectors to see if any are loose. I checked fuses. OK

Have not pulled any sensors or checked voltage or oHms yet. Car turns but won't start. Any clues?

2nd question: Would all that coolant foul the O2 sensors? Can these be cleaned?

1st of all, I don't think a bad 02 sensor will not allow the engine to start. It's only an emissions device!! Any way according to my '98 C/K manual for 5.7 light duty (this is a little confusing) it's midway between the cat and the muffler in the right bank(passenger side) exhaust system. The book shows this system going into the left side of the muffler.

As for no start, you need to check fuel press(can U hear the fuel pump run for about 2-3 seconds when U turn the key to "run"?) and ignition. Let us know and we'll try to help some more............Steve

I notice you went and filled it up with gas before the light came on. When those trucks are at the gas station filling up the tanks..that is the WORST time to get gas, because they gas they put in blows all the crap off the bottom of the tank and mixes it with all the gas so when you pump your gas you get extra dirt and junk in YOUR tank and you may have killed the fuel pump. Im not sayin the truck was there right at the time you got gas but if he was there a little before and now you have an SES light i would guess your fuel pump screen is clogged and your pump is crappin out on you. 02 sensor won't cause it not to start, its only to help with the fuel/air ratio in your engine for emissions. Double check everything before you go for that pump...its not gonna be fun. Hope this helps.

I've located all four sensors. And there are two catalytic converters (cc's.) Estimated guess is that bank 2 sensor 2 is right passenger side, in back of the right side cc.

But surprise surrrrrprise!!!! After sitting there for about 48 hours, I go out and turn the key and she starts up. Stays at idle no problem but I'm not leaving the driveway until I'm sure I won't get stuck somewhere. The SES light is no longer showing. So I cleared the code from my codescanner. No new codes yet.

Let her idle for a while. Because you mentioned the fuel pump, I listened for it while idling. I can hear the fuel pump whirring away and it is fairly noticable. Pitch of the whir seems to rise and fall. I'm not sure if it always made this loud a whir and I'm only noticing because you mentioned it!

Or is it more noisy because it is going bad? Hmmmmm...where is Ed Grimley when you need him?

After 77k miles it may not be a bad thing to just put a new one in anyway based on what Ive learned here they don't last anyway. Problem is what to do with appx 38 gallons of gas. At 7lbs/gallon, thats 266 lbs weight that wants to come down when I drop the tank!

Why would I get that O2 sensor reading if the fuel pump is going bad?

Why would I get that O2 sensor reading if the fuel pump is going bad?


The 02 and fuel pump are two seperate issues. My '98 Sub has had a loud pump from the get go. It now has 117k and still sounds the same, although I do have one on the shelf if or when it goes bad. $280 from GMPartsDirect.

Throw a pump at it if you want, but there's a lot of electronics involved determining whether the pump runs or not that needs to be checked before I'd just replace a pump for the hell of it!

Go drive it for a while before you jump to any conclusions...........Steve

02 sensor locations go like this.
Bank 1 sensors are on the side that No. 1 plug is on.
On yours bank 2 sensors are passenger side.
And sensors 1-2-3 are counted from first sensor on or right behind exh. mainifold
Bank 2 sensor 2 = second one back on passenger/right side.
But like was said a 02 sensor codes will not cause a no start.
Hard to start cold or no start.
Check cold start/cranking fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

Thanks for your help.

I'm shopping for a fuel pressure tester and Sears has a Sunpro for $40. It looks like it has a schrader valve connector in the picture. Any other recommendations?

Sears tools are usually good.
The price sounds good.
Just make sure the gauge goes up to a 100 lbs of ressure.
I like a hose long enought to tape to windshield or mirrow for road testing.
Let us know how it goes. And remeber the fuel pressure has to be up to specs.
Even 2-3 lbs low can give you a hard/no start cold.
MT

If your fuel pump is speeding up and slowing down the pump is most likely bad and needs to be replaced. They should be a soft continuous hum VERY low not noisey. you should not here the pump from inside the car AT ALL. You can check the fuel pressure and everything if you want but the pump would be my guess. The 02 sensor could be bad from the pump but not directly. The o2 sensor picks up the air/fuel ratio. If your pump is crapping out without going all the way off, your not getting a constant ratio. You sensor has to range to compensate for it to run well. Its all electronics and easier to show you then to explain it. But all your 02 sensors may be having to range all crazy too lean and too rich back and forth and that sensor may have just crapped out. If you've never replaced them thats probably what happened. Hope this helps, take care.

pressure 55psi reading so that is likely the issue. She quit running again right after I ran the pressure test. BTW the filter has about 15K. I'm going to change the filter before I go any further. But again the SES light came back on so the fuel mixture must be confusing the sensor/computer like you say.

Now the fuel pump is not even starting when I turn the key. I'm trying to drain the tank 28 gallons so far with a syphon/pump thingy that works pretty good except I cant seem to get to the last 10 gallons I believe are still in there. My neighbor loves me for filling up their kids car though LOL

Possible that the tank is now empty resulting in fuel pump not starting. No way to tell until I drop the tank.

Also make sure the fuel pump is getting full 12/13 volts and a good ground.
You can check it at the wiring plug at fuel pump and make sure the plugin is good.
MT

Your last post on how far to drop the tank before disconnecting the lines is not showing up for some reason.
Just drop it far enough to get them unpluged and watch for a hose /hoses on front end on tank to.
Them plastic fittings and gas lines will break so do not stretch them. :grinyes:
Good luck and let us know how it goes.
MT

One other thing I find that helps on a lot of them is to drop the drive shaft.
That gives more room to reach up over the side of the fuel tank and get the fuel lines and wires disconnected and hooked back up.
MT

only had to drop tow bar took tank out and cleaned completely, dried with compressed air. new fuel pump is in, new wiring harness, new fuel filter. Runs good but only 10 miles so far. No SES light. Pressure - 56 PSI - only standing can not drive it with pressure gauge so need a longer hose so I can tape it to window. Somewhere I got impression that driving I may get higher pressure. If not, could be fuel pressure regulator. Getting some water out the tailpipe but less since I fixed intake manifold gasket. Need to check cat. converter because somewhere else I read coolant in the oil may damage it.

Read and read more posts about fuel pressure regulator. Have not done any diagnostics. If FPR faces into the plenum, it may have gotten coolant crap on it.

It sounds like you found the sore spot. Glad you got it going.
The fuel specs are 60/66 on it shoud idle about 60-62 and full load should jump to 65-66 or engine start should be 65-66.
Or in other words 60 full vacume and 66 no/low vacume under load or heavy pull on engine.
But if it starts good cold you fuel pressure is close to specs.
It could be the gauge is off a little or need calabrated.
MT

All you have to do for the Cat Converter is slide under the car and hit it with your fist. If you hear rattling, its turned to crap. If you don't here rattling and it doesn't glow a bright orange after you drive it lol, it should be alright.

All you have to do for the Cat Converter is slide under the car and hit it with your fist. If you hear rattling, its turned to crap. If you don't here rattling and it doesn't glow a bright orange after you drive it lol, it should be alright.

One of the best test for a stopped up cat is a back pressure gauge also to check if it is working right you need to watch and check your 02 sensor readings.
But what does cat checking have to have to do with this post. :grinyes: :lol: