What did you do to your NBS GMT800 Tahoe/Yukon Today?

mikez71 · May 1, 2026

Noticed my Navgation/radio unit is noisy!
Even when it's turned off.. It's only get's quiet after I take the key out.
Any fix for this?
--------------------
UPDATE? The next time I drove my Nav unit was not noisy.. weird..
Sounded like it was spinning a CD or something, but there was no CD in there..

I did snip the key in ignition switch wire.. green wire before I taped it up..
Could have de-pinned it at the steering column connector.. oh well...

It got rid of the key-in/door-open chime, but not the ignition in run position chime..
These chimes are killing me..

Also paid for HPTuners credits for this old jalopy.. enabled power enrichment.
Had to get rid of the P0894 code so trans won't go into full line pressure mode.

LsHart · May 1, 2026

I also put in a order for smoked foglights to match.

LsHart · May 1, 2026

Also great news. I ordered these today. 22 x 9.5 for the front and 24 x 10s for the rear. I'll take pics as the project progresses. Time to chop!!!

yukon-coRn · May 2, 2026

Finished installing a radio with a smaller screen (old one was a freakin' 10" tablet thing). Pretty fussy ordeal and I haven't tested the backup camera yet.

dps01 · May 2, 2026

It has an actual knob for volume…

mikez71 · May 2, 2026

I drove my Suburban to the JUNKYARD!

(To grab a Z71 roof rack.. )
It's been decades since I've been there...
I had to climb on the roof, and was pleasantly surprised it could support my weight without popping..

And now that the ridiculous chimes are 'fixed', I can focus on less important things...

..like my slipping torque converter, exhaust leak, bad knock sensor, squeaking brakes, and whatever causes that knocking feeling that goes through my steering shaft...

strutaeng · May 2, 2026

mikez71 said:
I drove my Suburban to the JUNKYARD!

(To grab a Z71 roof rack.. )
It's been decades since I've been there...
I had to climb on the roof, and was pleasantly surprised it could support my weight without popping..

And now that the ridiculous chimes are 'fixed', I can focus on less important things...

..like my slipping torque converter, exhaust leak, bad knock sensor, squeaking brakes, and whatever causes that knocking feeling that goes through my steering shaft...

...scared me there for bit! LOL

mikez71 · May 2, 2026

This truck does belong in the junkyard. Sprung two new codes today! That's a total of 5 codes so far..

Less important one, U1056, Tech-2 says lost communication with RTD (suspension module)
OK, I know I can't get those autoride shocks anymore anyways, so plan for a liftkit with new shocks someday..

But the first code below is a GM code forsure.
(Gotdam Mothervucker)

Freeze frame shows I was at a stop, idling in drive, in open loop.? 21% engine load seems high for idle?

I hope I don't need to pull the cats and hope they're not broken.. Maybe I can clean them with some dawn dishsoap or something..
Cat tests had previously passed.. more than once as I kept resetting all these other codes that keep popping up!
Maybe some new O2 sensors and new exhaust gaskets will help? I dunno..

This thing is trying to kill me..

mikez71 · May 3, 2026

Looked at my downstream O2 logs to see what might be tripping the cat efficiency code.
(Bank 2 in yellow)

Slower warmup than bank 1.. Maybe partly because upstream sensor is slower to warmup..
But sensor drifts lean. This is before cat is warmed up? Hoping it's just the sensor dying in a way that doesn't trip the o2 sensor code..

Dips more often than bank 1. Often during light throttle or lifting after heavier throttle.

Spiky peaks and dips.. Could an exhaust manifold leak cause this? It's much further upstream than this bank 2 cat and o2 sensor...
There is a joint before the cat, but no obvious sign of leakage (no soot trails).

Lean reading at idle here. Driving around just has more dips/valleys. But longer periods of idle read lean. Hopefully just an exhaust leak..

Sounds like secondary O2's are supposed to be more steady state, and not lean..
Sometimes Bank1 dips too, sometimes they mirror each other, but bank2 definitely dips more frequently and drifts lean..

Backpressure test and and checking for exhaust leaks today...

mikez71 · May 3, 2026

Did a back pressure test. Looks good, maybe 1.5psi at 4000 rpms.. Thats a relief.
Smoke testing exhaust next..

Scottydoggs · May 3, 2026

mikez71 said:
Looked at my downstream O2 logs to see what might be triping the cat efficiency code.
(Bank 2 in yellow)

Slower warmup than bank 1.. Maybe partly because upstream sensor is slower to warmup..
But sensor drifts lean. This is before cat is warmed up? Hoping it's just the sensor dying in a way that doesn't trip the o2 sensor code..
View attachment 484295

Dips more often than bank 1. Often during light throttle or lifting after heavier throttle.
View attachment 484296

Spiky peaks and dips.. Could an exhaust manifold leak cause this? It's much further upstream than this bank 2 cat and o2 sensor...
There is a joint before the cat, but no obvious sign of leakage (no soot trails).
View attachment 484297

Lean reading at idle here. Driving around just has more dips/valleys. But longer periods of idle read lean. Hopefully just an exhaust leak..
View attachment 484298

Sounds like secondary O2's are supposed to be more steady state, and not lean..
Sometimes Bank1 dips too, sometimes they mirror each other, but bank2 definitely dips more frequently and drifts lean..

Backpressure test and and checking for exhaust leaks today...

scan the o2's with mV. (millivolts.) when you scan just the volts they are supposed to dance up and down rather quickly. in mv when you go wot they should lock in and read around 900. if they dont read close to the same the one with lower value could be bad. or if it hits 930 then drops off thats one's def a problem.

mikez71 · May 3, 2026

Scottydoggs said:
scan the o2's with mV. (millivolts.) when you scan just the volts they are supposed to dance up and down rather quickly. in mv when you go wot they should lock in and read around 900. if they dont read close to the same the one with lower value could be bad. or if it hits 930 then drops off thats one's def a problem.

What's the difference logging in Volts vs mV? It's not just 1000 times the value? .5 vs 500?

I was focused on downstream O2's, but maybe I need to look at upstream more..
They seem normal to me here...
If anything, the sharp downward spikes on B2S2 seem odd to me..(circled)

Tapped cat with a mallet, no rattle.
I put a wrench on that sensor, it's tight. Possible the sensor leaks?
Thought I read that o2 sensors reference atmosphere through the gaps next to wire insulation?
(looked it up, apparently just the zirconia type needs reference air, which I believe these are)

Should have taken a photo, but at least the sensor looked clean. Little reddish tint like you see on sparkplugs, heard its fuel additives like techron?

Smoke test through the primary O2 port showed nothing! But no smoke came out the tailpipe when I pulled the plug. A little wind, but lots of smoke when I pulled the hose out of the O2 bung...

Thinking I will gamble on a new sensor.
Spikes seem weird, and signal sometimes drops lean when other sensor is gradually ramping down. Not complete failure that could set an O2 code, but intermittent or dead zone type failure??

Scottydoggs · May 3, 2026

mikez71 said:
What's the difference logging in Volts vs mV? It's not just 1000 times the value? .5 vs 500?

I was focused on downstream O2's, but maybe I need to look at upstream more..
They seem normal to me here...
If anything, the sharp downward spikes on B2S2 seem odd to me..(circled)
View attachment 484342

I put a wrench on that sensor, it's tight. Possible the sensor leaks?
Thought I read that o2 sensors reference atmosphere through the gaps next to wire insulation?
(looked it up, apparently just the zirconia type needs reference air, which I believe these are)

Should have taken a photo, but at least the sensor looked clean. Little reddish tint like you see on sparkplugs, heard its fuel additives like techron?

Smoke test through the primary O2 port showed nothing! But no smoke came out the tailpipe when I pulled the plug. A little wind, but lots of smoke when I pulled the hose out of the O2 bung...

Thinking I will gamble on a new sensor.
Spikes seem weird, as well as some continuous lean readings at idle...
Signal sometimes drops lean when other sensor is gradually ramping down.
Not complete failure that could set an O2 code, but intermittent failure?

down stream o2s are only there for cat efficiency, the up streams work with the maf to control fueling. you can remove the down stream o2s and delete their codes and never notice a thing. when scanning voltage, thats what they do 0- 9 volts over and over. up down up down.

mikez71 · May 3, 2026

I know, but my code is for cat efficiency, and I need to smog this.
Not sure if cat test will show 'complete' with secondaries disabled..

From what I'm reading, secondaries should not oscillate much once cats are warmed up.
Reading richer means cats are working better, converting the oxygen.
They oscillate fine when cold start.

I think mine is not the lazy sensor failure mode, but some other failure mode..
Guess I'll find out when I get a new sensor...

Scottydoggs · May 3, 2026

mikez71 said:
I know, but my code is for cat efficiency, and I need to smog this.
Not sure if cat test will show 'complete' with secondaries disabled..

From what I'm reading, secondaries should not oscillate much once cats are warmed up.
Reading richer means cats are working better, converting the oxygen.
They oscillate fine when cold start.

I think mine is not the lazy sensor failure mode, but some other failure mode..
Guess I'll find out when I get a new sensor...

your in ca? you have aftermarket cats by chance? or super high miles? being you cant delete codes in ca any more, the only other option is to try adding anti fouler extensions. they pull the o2 out of the tail pipes so they read less of the gasses in the pipes.

mikez71 · May 3, 2026

Factory cats and 150k.

Yea, I worry the smog station will catch those plug extenders. (or actually plug retractors?)
They seem pretty focused on their visual inspection, but the rules definitely suck and cost more $$$ for nothing...
I would prefer to spend the money on fresh primary sensors, but instead am patching up this monitoring system..

BTW, the primary I pulled out to do the backpressure test looked like a bosch style sensor, not original?
Or did GM change suppliers?

I see no reason my cats should not be good. ?
No discoloration, no clog, no rattle, clean primary sensor. (though it may have been replaced, it's running clean as long as it's been in there)

mikez71 · May 3, 2026

Pulled my bank 1 O2 sensor (Boy these sensors are easy to reach on the LQ4!)
It does not look anywhere as good as bank 2 sensor, which looked really clean.
Both are Bosch style sensors..

Here is bank 1 sensor (driver side right?)

What do you guys think? Oil contamination? And/or over fueling? Maybe exhaust manifold is leaking with front and rear bolts broken off..
Bank 1 tends to read 2% leaner.(LTFT 2% higher most of the time)

I hope to replace both primary sensors next order.. Wonder if I should soak my pistons when I install new plugs..

Gus1980 · May 3, 2026

Washed mine and took it for a drive. Got it for sale so it’s been sitting out, but after driving it I struggle with selling it.

strutaeng · May 3, 2026

mikez71 said:
Pulled my bank 1 O2 sensor (Boy these sensors are easy to reach on the LQ4!)
It does not look anywhere as good as bank 2 sensor, which looked really clean.
Both are Bosch style sensors..

Here is bank 1 sensor (driver side right?)
View attachment 484371
View attachment 484372

What do you guys think? Oil contamination? And/or over fueling? Maybe exhaust manifold is leaking with front and rear bolts broken off..
Bank 1 tends to read 2% leaner.(LTFT 2% higher most of the time)

I hope to replace both primary sensors next order.. Wonder if I should soak my pistons when I install new plugs..

They look okay to me, but I don't really know what they should look like?

You can always swap them, from L to R to see if your running conditions also switch. It's kinda like parts cannon approach, but that's an exception because it doesn't cost anything except time...

mikez71 · May 3, 2026

strutaeng said:
They look okay to me, but I don't really know what they should look like?

You can always swap them, from L to R to see if your running conditions also switch.

Exactly what I was thinking! They come out real easy so I'll do that tomorrow and take a comparo pic.
Be interesting to see if the sensors read differently, or if the cylinders/injectors are imbalanced more or less..
Thinking about running some cat cleaner through it.. Never know about the additives myself..

I will see what my plugs look like in a week when my new ones arrive..
Planning to go with Denso primary O2's someday, unless they're no good?... (Would save $60 over an OEM pair)

What did you do to your NBS GMT800 Tahoe/Yukon Today?

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