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2002 Silverado 2500HD 6.0L Power Falls Flat after Warmup

RayMich

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Good afternoon and Happy New Year to ALL.

I am having a major problem with my son's snowplow truck and I hope that someone here can help us diagnose and fix it.

The truck is a 2002 Silverado 2500HD 4WD with the 6.0L engine and auto trans. It has approximately 185,000 miles.

He bought this truck 6 years ago. It has been serviced every 5,000 miles and it has run great up until 3 weeks ago.

The truck runs fine when cold, but after running for 5 minutes or so, it falls flat on its face, starts running rough and won't go over 20 MPH.

My code reader FIRST detected the following codes:

P0131 - O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
P0154 - O2 Circuit No Activity Detected (Bank 2 Sensor 1)
P0300 - Random Multiple Misfires Detected
P0332 - Knock Sensor 2 Circuit Low Input (Bank 2)
P0461 - Fuel Level Sensor A Circuit Range/Performance
P0463 - Fuel Level Sensor A Circuit - High Input​

My son did say that the fuel gauge has not worked for a couple of months, but the truck ran fine until 3 weeks ago.

One of our local exhaust shops told my son that the Mass Air Flow Sensor was bad and both Cat Converters were plugged, and with much reluctance my son agreed for them to replace both converters and a new muffler to the tune of $889.00 because he needed to get it running ASAP since he is missing out on a lot of snowplow work.

- Leaving the shop, the truck ran great for about 5 minutes then the power fell right off, the SEL started flashing again, the engine started to misfire and it would not go over 20 MPH even with throttle floored.

The Mass Air Flow Sensor and air filter were replaced. All spark-plugs and plug wires were replaced TWICE. All the plugs appear to be getting a nice hot spark. Interestingly, all four plugs on the RH (Passenger Side) are getting fowled, while those on the LH (Driver Side) look fine.

If we let the engine cool down to ambient temperature and clear all the codes, it will run great for the first 5 minutes when started, then as soon as it warms up while driven, the Service Engine Light starts flashing again and power falls off. Checking the codes again, we get these codes.

P0154 - O2 Circuit No Activity Detected (Bank 2 Sensor 1)
P0300 - Random Multiple Misfires Detected
P0332 - Knock Sensor 2 Circuit Low Input (Bank 2)
P0461 - Fuel Level Sensor A Circuit Range/Performance
P0463 - Fuel Level Sensor A Circuit - High Input​

He tried to replace the Bank 2 O2 Sensor 1 on the passenger side, but it is rusted on and the hex started to strip, so he stopped trying.

If someone can please help us troubleshoot this so we can get it fixed and back on the road, it will be greatly appreciated, because right now the truck is out of service and has already cost my son over $6,000 in lost revenue.

Thank you in advance for any help you folks can provide.
 
Last edited:

Will L.

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#3
swap left and right O2 sensors, clear codes and try it.
Same codes or does the other bank shut down.

For everyone in the future: if you suspect a plugged cat, cut the pipe if it cant be unbolted and drive with it open to see if massive power loss goes away before spending $ for a new cat which will require unbolting or cutting... all auto parts stores sell exhaust band clamps to repair a cut pipe.

Loosing a bank in a LS is not unheard of, but usually requires live scan to see what is happening first and what things are just symptoms. A good driveability tech can be worth their weight in gold, and 99.9% of the time are the most arrogant guy in the shop from it.
 

WarWagon

Well it hits on 7 of 8...
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#4
Stuck injector or fuel leak dumping fuel into that bank? Oil getting into the combustion chamber? Both can foul or melt cats down and they plug from being melted. Not saying they were bad, but, they could be and ruined the new ones. No O2 activity IMO indicates said fuel flood condition. Engine oil diluted with gas?
 

Will L.

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#5
I thought that too, but if injector stuck, it should be that specific cylinder like p0302 etc... p300 means not repeat specific cylinders. The whole bank is probably going nuts.

Does that still have only 1 fuel pressure regulator for all 8 cylinders, or one for each side?
 

Will L.

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#6
Also wondering if the bad tank sensors could be causing issue through module- is mpg lie-o-meter reading crazy mpg after warm up but ok during warm up?
Convinced somehow the O2 sensor going into loop is key triggering something to dump more fuel instead of less.
 

THEFERMANATOR

FRANKENBURBAN
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You have a closed loop error going on. Just for kicks, try unplugging the O2 sensor in question, and see what happens. The 0411 PCM should revert back and use the functioning upstream O2, and run both banks the same. Many times problems like this are due to cracked intake gaskets. As soon as it goes to closed loop, the O2 sensor sees the over rich oxygen, and begins dumping fuel which fouls out that side. The knock sensor code is fairly common on early LS's, and will probably require a new knock sensor harness and knock sensors. You will probably need a pipe wrench or something to get the frozen O2 sensor out. This could also simply be a bad O2 that is grounding out as soon as it goes closed loop, but I would have expected the PCM to code for it, and ignore it(not sure if the 512kb 0411 can do this or not). Start by unplugging that 1 O2 sensor, and see what happens. It would also help to get a scanner on it, and see what the PCM is commanding for fuel to each bank as well as monitoring the O2's to see if theres any activity, and what kind there is.

As to fiel pressure regulators, I don't know of any LS engine with 2 regulators. 02 is also the year where it might have a rail mounted regulator, or it might not. It's a crap shoot, just like how in 04 it's a crap shoot if you have a replaceable fuel filter. If it does have a regulator problem, they show up after it has been running, then shut off for 10-15 minutes, and restarted. The engine will be loaded up from the fuel traveling through the vacuum line into the intake plenum. It's easy to check for. Find the regulator mounted in the fuel rail, drivers side, just forward of the mid way point. Remove the vacuum line, and look for traces of gas inside of it.
 

RayMich

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I've been super busy and haven't had much time to check in here.

Thank you all for the responses.

Air filter is new and dry.

I asked my son about the fuel gauge not working and he said that it has not worked for a few months and the truck ran fine 'till about 3 weeks ago.

The problem comes when the truck goes closed loop. If it was a stuck injector, I would expect it to run bad all the time.

I was very suspicious of the plugged cat converter diagnosis, but my son was willing to do whatever it took to get the truck running ASAP and two exhaust shops had told him it was a plugged converter, so he saw it at the quickest fix, which in reality turned out to be WRONG and expensive. By the time I got involved, the new converters and muffler had already been installed.

Unfortunately, neither one of my code readers will do anything more than read or clear codes. So I can't get any other live data.

I will see if we can swap the O2 sensor wires. Don't know if the wiring is long enough.

Will again check for any intake leaks. But when cold the engine idles fairly smooth. Once the engine warms up and it goes closed loop it starts missing all the time.

I don't know if I can fit a pipe wrench on that froze O2 sensor, but will try. It may be a while before I can get to it. Son is in the process of moving (sold his house and has to be out by Monday 1/8) and I don't have room in my garage. Maybe his mother will let him work in her garage. With ambient temps hovering around ZERO for the last few days it is impossible to work on it outside.

Thanks again for all the suggestions. I will post back with any results as soon as I can work on it again.
 

Will L.

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#10
No, the wires will not be long enough to swap them to other sensors.
Ferm is saying disconnect the wire from the pass side.
I was saying one step farther and swap sensor, as in remove both from exhaust then install them in the other sides. If hard to remove, torch and the air hammer style socket works wonders.

Follow his suggestion- it sounds easier to me and will get the results.
 

RayMich

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OK. We will try that. I may be a couple of days before we can get to it, since he is in the middle of a move.

The only torch we have available is a propane torch. Don't know how well it will work, but worth a try.

Thanks.

Best regards.
 

btfarm

330,000 Worth and counting
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You may recall from the test long ago Ray that a 50-50 mix of acetone and ATF is about as good a penetrating oil as you can get. Nice to see you around again BTW...
 

RayMich

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Well, Folks! - Looks like we are on the right track to success.

I just got a text message from my son where he said that he unplugged the offending O2 sensor and wrapped both connectors in a plastic baggie. He cleared all codes and drove the truck.

His comment is, "Runs Great!"

The only codes now are
P0154 - Oxygen Circuit No Activity Detected (Bank 2 Sensor 1) which is to be expected.
P0463 - Fuel Level Sensor 1 Circuit High Voltage (still doesn't work, but does not prevent him from working.)
B0077 - Driver Side Impact Sensor (This was probably damaged while plowing.)

He tells me he will try to replace the bad O2 sensor tomorrow. (He says that he is renting a special tool for removing O2 sensors.) But at least the truck is running now. :)

I want to thank everyone here for the excellent suggestions you have given me. If only I had known about the problems he's been having with this truck before he paid to replace the cat converters, so I could have checked the fountain of knowledge in this forum, he could've saved all that money he paid for replacing both cat converters.

I will come back with an update once the bad O2 sensor has been replaced.

Thanks again guys, you all are GREAT! :happy:
 

THEFERMANATOR

FRANKENBURBAN
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Sounds like the O2 is pulling to ground which as soon as it goes closed loop, the ecm freaks out and goes nuts. I've chased this before, and had a friend who has worked on GM's for a long time tell me to try unplugging the 02. It's helped me many times in chasing problems that I thought were O2 related, but weren't setting O2 codes.
 

RayMich

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Tried to remove bad O2 sensor. Stripped the hex. Need to find someone with a hoist and a torch to get better access to the bad sensor. Making appointment with mechanic. Can't get to it 'till Monday or Tuesday. :bigtears:

At least he is still able to make some money plowing with the bad O2 sensor disconnected. Hopefully it will hold until sensor can be replaced.

He is going to need to find a newer truck if he wants to continue plowing. This one is getting tired.
 

RayMich

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Ended up having our repair shop replace both the upstream and downstream O2 sensors on the passenger side. The wire on the downstream sensor broke off when touched. So that one had to be replaced as well. While they were at it, I had them fix a T-Case leak and replaced all 4 prop-shaft U-joints (F&R) that were pretty well worn. Mechanic tells me that it still has a small intake manifold leak but at least the truck is driveable again. Son said he was able to go 90 mph on the highway and NO Service Engine Light. That is a long way from the 15 mph maximum speed when the problems started. Hopefully this truck will hold out thru the rest of the snowplowing season. Will need to replace it soon.

Code reader now shows NO powertrain codes. But the Airbag light is still on and still getting the B0077 - Impact Sensor code, so that will need replacing.

Thank you everyone for your help in diagnosing these problems.
 
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