2001 suburban 2500 sensor issue!?

C.Berry

C.Berry

Bad News
Joined
Aug 10, 2008
Location
Blacksburg, Va
picked up w 01 burb 2500 6.0/4l80e! The truck had a exhaust leak at egr down pipe so I pulled exh manifold and replaced all the gaskets to block and egr! Truck was running great could barely feel gear changes more power then I could need!
All of a sudden I get a blinking SES light only while idling codes showed p0300,p0332(KS), and bank 2 o2 sensors bad! Replaced upstream o2 and no change sent it to a “mechanic” to put on high dollar computer and he said it was the bank2sensor2 causing the issue!
Well I know better then that bc it was unplugged since I bought a month ago and truck ran flawlessly! Now what it does when started up it’s rough idle then settles down and idles decent, but when I drive it the transmission seems to not want to find a gear and stay in the gear unless I’m barely feathering the gas... I just picked it up from shop he said they got all codes cleared but as I figured SES was on when I started it! I was charged $200 to wire a pigtail on a o2 downstream sensor and to pull up codes, so I’m pissed but was trying to be proactive instead of throwing parts at it!! Anyone have a idea where I could start? I’ve become familiar with the 4l80e bc the issues I had with my 99 burb but this is something electrical or sensor related I feel like and I suck at diagnosing electrical issues!! Thanks in advance hope everyone had a good. Holiday season!!
 
Rough idle on start up.. injector leaking? Watch the misfire graphic an see what cylinders are misfiring on start. Go from there. So the trans acts like neutral unless your barely on the throttle or you have to let off to shift or what?
 
a_kelley said:
Rough idle on start up.. injector leaking? Watch the misfire graphic an see what cylinders are misfiring on start. Go from there. So the trans acts like neutral unless your barely on the throttle or you have to let off to shift or what?
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I thought injector leak bc I smelled gas in oil but though it could be from bad o2 sensors!?? No trans acts like it’s in gear changes gears fine but if I throttle into it it will not stay in the gear or it will drop down a gear if hard throttle it acts like it’s in neutral tho and revs!
 
Not sure on trans issue. Usually the other way around. (And I'm more familiar with 4l60e)

O2 could make it run rich, but typically that won't contaminate the oil. That screams leaky injector. Especially if you have a longer crank time. (Though if you turn on ignition, wait 2 seconds then crank, you may not notice, especially may not notice normally if the fuel pump is good and strong)

Edit: regarding trans issue - throw a gauge on it. See what the pressures are doing when you use light throttle vs heavier throttle. How many miles on it? I'm thinking your sucking the pan dry for it to fall into neutral - no fluid, no pressure, no clutch engagement. (Seeing how all clutches in all automatics are fluid pressure operated). HTH
 
a_kelley said:
Not sure on trans issue. Usually the other way around. (And I'm more familiar wit 4l60e)

O2 could make it run rich, but typically that won't contaminate the oil. That screams leaky injector. Especially if you have a longer crank time. (Though if you turn on ignition, wait 2 seconds then crank, you may not notice, especially may not notice normally if the fuel pump is good and strong)

Edit: regarding trans issue - throw a gauge on it. See what the pressures are doing when you use light throttle vs heavier throttle. How many miles on it? I'm thinking your sucking the pan dry for it to fall into neutral - no fluid, no pressure, no clutch engagement. (Seeing how all clutches in all automatics are fluid pressure operated). HTH
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Had codes read again and now I have a p1639 pcm low voltage code? I drove it last night and it started out screwing up got about 4 mikes down road and it stopped and drive flawlessly again so I stopped turned it off started back up and it started process back over it’s random but when idling it’s obvious and then causes SES to blink bc of misfires! Which I know is bad mojo when they blink but only does that when idling!!
 
5v sensor reference voltage has a short, maybe a bad sensor or a bare wire. I'll pull the diagrams & diag steps & related info when I get back to shop.
 
a_kelley said:
5v sensor reference voltage has a short, maybe a bad sensor or a bare wire. I'll pull the diagrams & diag steps & related info when I get back to shop.
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Thanks man, I’m thinking it’s tps bc it’s to my understanding part of pcm 5v deal as you can tell my electrician terminology is piss poor... lol and my 99 2500 was similar but not as extreme when tps went out
 
If you tap into the sensor reference voltage and start unplugging stuff, you'll know when you get the failed sensor unplugged, since it'll go from 0v to 5v.

5v ref 2 being low voltage
Blue 80 pin connector, pins 45 & 46, connect test light to 12v to each pin, if it lights check sensors and wiring for shorts

P1639 related sensors/pins
Tps (pin 46)
Fuel tank pressure sensor (pin 45)

I'd think your on the right track with tps. I'm surprised there aren't a bunch of sensors on the 5v reference.
 
a_kelley said:
If you tap into the sensor reference voltage and start unplugging stuff, you'll know when you get the failed sensor unplugged, since it'll go from 0v to 5v.

5v ref 2 being low voltage
Blue 80 pin connector, pins 45 & 46, connect test light to 12v to each pin, if it lights check sensors and wiring for shorts

P1639 related sensors/pins
Tps (pin 46)
Fuel tank pressure sensor (pin 45)

I'd think your on the right track with tps. I'm surprised there aren't a bunch of sensors on the 5v reference.
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You know I thought there would be way more also but from what I see it’s just those you mentioned! Just picked up a tps so gonna throw it on and cross fingers! Thank you if that don’t work I’ll have to research and figure out the testing of the sensor voltage!
 
I hope the sensor thing works out but I know this may be a stretch but they are a completely electronica controlled system so also make sure you are checking all of your grounds. I had a HMMWV once with the O/D trans it gave us fits in Iraq. Put a new trans in and still had issues. Old (more experienced) motorpool guy found a corroded ground wire, cleaned it up and, boom. No more issues.
 
a_kelley said:
If you tap into the sensor reference voltage and start unplugging stuff, you'll know when you get the failed sensor unplugged, since it'll go from 0v to 5v.

5v ref 2 being low voltage
Blue 80 pin connector, pins 45 & 46, connect test light to 12v to each pin, if it lights check sensors and wiring for shorts

P1639 related sensors/pins
Tps (pin 46)
Fuel tank pressure sensor (pin 45)

I'd think your on the right track with tps. I'm surprised there aren't a bunch of sensors on the 5v reference.
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Well no good on new tps... I thought I smelled gas in engine compartment does bad fuel tank pressure sensor cause a p0300 code also? Multiple misfire?
 
Bad ftp would not necessarily cause a miss. It's more to check evap system, but since the reference voltage is shared, could I guess in theory cause a miss because tps signal is missing. Try unplugging it. It's the small 3 pin connector on top the tank. On the 1500/2500 you can reach it over the frame. It could also be a shorted wire..
 
So I picked up a fuel pressure sensor thinking it was in my fuel tank got the tank dropped to throw in sensor and this is what I had instead of what they gave me...? Black one is the new part no clue what the other one is tho!?
 

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a_kelley said:
Some didn't use the ftp sensor and some did.

Double check wiring for shorts going to the tps.
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Holy hell lol why’s CHEVY gotta do this to me lmao ok gonna run down wires to tps! I didn’t know not having fps was a option
 
Went through wiring from tps nothings standing out to me I suck terribly at electronics tho! I noticed when I unplugged iac the truck kept running the same as it was which is awful and low idle but that don’t explain the p1639 and p0300...
 
P1639 is something grounding out reference voltage #2. It may or may not be related to the random misfire. I'm a ways away but your welcome to bring it over to my shop
 
a_kelley said:
P1639 is something grounding out reference voltage #2. It may or may not be related to the random misfire. I'm a ways away but your welcome to bring it over to my shop
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I wish I could but the misfire or p1639 code is now causing very rough shifts through all gears, that leads me to believe it’s tps wiring related!? I’ll be tearing into that tom after work I’m driving the other burb so I’m not doing major damage to this one! Could it be just grounds to block and frame or the ground for the tps or what else is on the 5v reference? I’m a damn slacker I’ve needed to learn electrical for vehicles years ago I just fear frying all the crap bc of lack of knowledge on the subject!
 
And wiring diagrams seriously make me feel like I’m a child learning to read a new language after just learning the English alphabet... lol sad but true
 
No. You'll be looking for a chafed wire/loom. Check make sure the bulk harness isn't laying on anything, or where it is, inspect it real close. The wiring diagram only shows fuel tank pressure sensor and the throttle position being on that same reference voltage circuit. Like I pointed out in a previous post, unplug the harness at pcm. Then probe both the listed terminals with a test light to power. If it burns brightly, (with tps unplugged) you have a short somewhere. Wiggle the harness till the light goes out and then tape it up and zip it up out the way to where it doesn't short out again.

Gargler turned up some hits regarding p1639 & your vehicle. May be worth looking those over.
 
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