I don't have access to wiring diagrams; but usually when 2, or 3, dash items aren't working, it's usually a ground strap problem.
In your case, I might check a fuse first.
The OBD2 circuit is fused from the same circuit as one of the 12v accessory ports. Do they all work?

 

i would have to agree with ray , intermittence usually means grounds bad or loose

 

If I pull the fuse that powers these items, the whole instrument cluster goes dark and the fuse does test as good.

A bad ground is usually the first place I tell everyone to go when there are issues that appear to involve multiple unrelated things.
All three of these items are always hot with the computer providing the ground to turn them on. So they effectively each have their own separate ground path. If the computer lost its ground nothing would work.

Per the service manual the ECM sends a signal on the data bus to the instrument clusters computer to tell the computer in the IC to turn on or off the light, all functions of the IC are controlled by 1 of 2 data bus lines.

Reading farther in the service manual I see I need to disassemble the dash to get to the connector to even start the test procedure.

I'm going in with my test lights, wish me luck.....

 

Good luck, let us know what you find.

 

When I find a solution to this I will post the results. When I was searching for this issue not one thread on this site got as far as a solution. I hate when people get hep and never say what worked.

 

There are approx 18 grounds on your truck , I would check under my dash drivers side , on my 98 it had a bar goes from one side to other and that holds the grounds

 

Just so we are all on the same page, the test light won't help on the LAN circuits. The PCM, or an IP computer will turn the light on, or off.
They are tied together by the LAN, but the LAN carries messages, not voltages, or grounds
You will not see the messages on the LAN.

The LAN is good and is providing communications with the PCM and all of the sub modules; I know this because you do not see any LAN codes.

At this point, your goal is to get rid of the Pxxx message, which indicates the MIL isn't lighting, I'd worry about it and not the other 2 problems.

And, the first thing I would check is the bulb. I've had lots of LEDs fail.

 

You are correct The MIL is the only thing that matters to get thru emissions.
OK, I got the dash all apart.
did all the tests in the service manual and they all check out as ok.
Brought the instrument panel into the shop and took it all apart to check the LED.
Put power to pin 5 and connected pin 18 to ground and the MIL light lit up just fine.
So the ECM is telling it to turn on and off and the LED is working.
So I took the bare IC circuit board back out to the truck and plugged it into the truck.
The MIL lit up at start just like it should, checked for codes and there was none.
So I beat it down to the test station and it still failed because when you unplug the IC it resets all of the readiness monitors.
ARRRGGGGgggggg

According to the service manual the signal to turn on the MIL is NOT on the buss, it is a dedicated wire from the IC to the ECM where the ECM provides the ground to turn on the light.
My scan tool does not have the capability to command the MIL on/off. so the best I can do is to turn the key on/off to make the ECM command the light on/off to check for the ground at the IC connector.

I am debating measuring the resistance of the MIL circuit and just wire in a resistor to lie to the ECM to get me thru the test.

I really hate just throwing money at a problem by buying new parts to try. Especially since I am out of work due to COVID. Intermittences really make me crazy, especially when I can not pinpoint what the problem is. Sometimes you do have to bite the bullet and thro parts at it till the problem goes away if you can not get it to malfunction while testing.

 

Jeff, just unplug a sensor, like an O2, that will bring up the MIL.
That makes sense that the MIL would be hardwired to the PCM, if the bus failed, there would be no way to signal the driver.
Good job so far.

 

It gets more fun.
In researching a replacement IC, according to the P/N on my IC it was only used in 2009 and 2010. My truck is a 2011. BUT and there always seems to be a BUT. My truck was built Sept of 2010, I wonder it it has leftover 2010 parts on it instead of the 2011 parts????

Best price I found so far on a reman IC with programing was $127. New with program is $350.
Best price on a ECM is a reman with programing for $250. New with programing is $460.
So IF I have to throw parts I will start with the IC first.

I HATE intermittent problems. I am not sure where to head next.

 

Jeff, I don't see intermittent here, you had no light, you took the dash apart now the light works, that's a dirty connection that is now working.
The light circuit is now working, or your OP code would have returned.
I don't know what you mean by resetting the readiness monitors; but that the next step, fix whatever you mean by readiness monitors.

 

This was intermittent before I did anything. That is what started this whole thing.
After taking it apart and putting it back together a bunch of times it is still intermittent.
I put it together and it was working so I headed for the test station but it stopped working by the time I got there.

You have to have a certain number of drive cycles (I think its 5 heat up / cool down cycles) to make it ready for the test

The code does return when it is not working. The code goes away while it is working.

 

Not sure yet but I think I may have found it.

The circled pin is the one that controls the MIL.
It sure looks a bit melted to me and it is hard to see in the pic but that contact also looks a bit tarnished.

I plan to use a tip cleaner for my OXY/ACT torches to get in there to clean up the contact in the connector and then bend the pin in the IC just a tad to help put more pressure on the connection.

I can not see how to extract the pins from the housing or I would get a new housing from a scrap yard. I may still do that later, even if I have to cut and splice all of the wires, at least there are only 14 of the 20 positions that are being used. There is easily enough slack in the harness to do this.
For right now I just want to get it thru emissions.

Then there is still the concern of WHY did that pin get hot enough to melt the plastic when it is just powering an LED?
Hopefully just a high resistance causing the heat.

 

Where was this connector located? Is this for the IC?

 

Well it is all back together and so far with the running around I had to do today, my McGuiver job is holding up. Now I just need to do enough driving to to reset all of the readiness monitors for the emission test.
I found a drive sequence that is supposed to reset everything to prepare for the test, I will try that drive tomorrow and if everything stays working I'll see if they can squeeze me in for the test.

 

I could be wrong; but I thought a battery disconnect would reset everything to ready.

 

A disconnect resets everything to NOT ready, It takes certain conditions to reset each monitor. The disconnect does clear all codes.

 

How To Reset Chevy Silverado 1500 Emission Monitors?

(RESOLVED - Click To View) I have a 1999 Chevy Silverado 1500 5.3L. I went in for smog test but it had not completed the emission monitors in the computer. I put another 400 miles on it, and still the same thing. I read the online procedure for a 2001 model. Should I do the same thing to get the...

www.smogtips.com

 

Ok, did a little research {we don't have emissions testing, so it's an area I'm not familiar with}, I now see your problem.
There appears to be a set of instructions to reset the monitors, I'm sure they're the steps your talking about
Good luck Jeff.

 

I sure wish we did not have the tests here, but Milwaukee WI is to close to Chicago and their pollution floats up here putting us over some air quality threshold, forcing us to test and run bad gas. It is only South east WI that has these requirements.

 

Well so far the light is still working and I still have 2 of the 8 readiness monitors that need to be set before I can take the emissions test.
I just had surgery and it may be a few months before I can drive any how.

 

jeff , instead of cutting any wires did you try just removing the wire connectors from the plug, and finding a nother or a new plug to replace it, i think places like napa has some replacement plugs, not sure if they have what you need. i only bring this up as i am one of those guys who would just cut and splice back when i was young and dumb, i have been cured of that bad habit, and dont advocate cutting any wires to anyone

 

Cutting wires is not my first choice. I do not have a pin extractor or replacement connector and pins. My current goal is just to get passed the emissions test, then I can fix it right at my leisure once I have healed up some.

 

I do understand your situation ,I would use Sodering , and shrink tube , then tape it up

 

Still trying to get the last 2 monitors to be ready for test. I think they should have been ready by now but they are not.
The last 2 are the catalyst monitor and the evap system monitor.

 

Well this is still fighting with me. before I can get all of the readiness monitors to clear the P0650 code comes back, It is not one of those codes that will go away if the problem goes away, I can not pass the test with a code present and I can not get the code to stay away long enough to pass the test. I missed by seconds one time, all the monitors cleared and no codes, I beat feet to the test station and all was good, in the middle of the test the P0650 popped back up and it failed, there was only about 30 seconds left in the test. Major BUMMER.

I have been messing with trying to get the stars to align but no luck. I think I kind of determined that it is heat related. The code seems to pop up if I go for a long drive and does not "fix" itself till it is cold again.

So today I took the dash apart again and hooked up all my test gear to mess with it and went for a drive. As soon as it blinked out I pulled over quick to do some checking.
The pink wire that supplies +12v power to the IC (Instrument Cluster) was reading zero volts. This is good in that it means it is not the Engine computer or IC that is bad but it is a power wire issue.
I immediately went to the under hood fuse panel where that wire is connected to fuse #48, a 10A ATM fuse. I tested both test points on the fuse and they both lit up. With zero volts still showing at the IC connector. So now I know that it is the wire between the fuse panel and the IC.

A long while back I had a situation where that #48 fuse had melted the plastic housing but did not blow. I believe it was due to a bad contact for the fuse in the fuse block. that would explain the heat generation without high amps blowing the fuse.

I have no idea how to get to the back of the fuse block to see if I can replace that terminal. Since the fuse test showed power on both sides of the fuse I am assuming that it is the circuit side of the socket that is bad.

So now the new plan.

I bought a ATM fuse tap that will plug into the bad socket and has a place for a fuse for that circuit as well as a second fuse to power a pigtail that comes out of it. I plan to put a good fuse into the pass thru socket and another 10A fuse for the pigtail. I will run a new wire from the pigtail to the IC connector to be able to back feed the circuit to power all of the other stuff that is not working as well as the IC. I even found a local source for the correct AWG pink wire so that the new wire will even be the correct color per the factory wiring diagrams.

But as I type this I am still not able to walk and it is a howling blizzard outside with 4-8 inches expected and drop to sub zero temps for the next week to turn this snow into concrete. So I do not know when I will be able get back out to it.

 

What a headache you have on your hand I bet at this point it’s it’s a cluster migraine. I mean, I’m reading this like a story you got me captivated. I’m sitting on the metaphorical edge of my seat!

 

Well I braved the cold and snow, It is 6°F with a 35 mph wind blowing so a wind chill of -19°F and 4 inches of fresh wet heavy snow that has frozen solid. I do not have a garage or any other shelter to work in.
I got the new wire run and connected at both ends, Initial testing looks good, But then so all of the other fixes initially. Now I just have to drive it around enough to get all of the readiness monitors to clear and then I can take it for a test again. 🤞🤞🤞
For now I have the wire thru the dash, out the drivers door, thru the dender to under the hood and into the fuse panel where it is connected to the add a circuit. A few tie wraps to hold it in place and it should be good enough to get theu the test and last untill warmer weather to do it much neater. My toes and fingers are frozen, I am still in a walking cast on my foot so there is not much insulation there. At least I will not need to ice it for a while......😁

Fingers are crossed that this one is the charm.🤞🤞🤞

 

Dear Mr. Jeff , I must say you are a natural storyteller. Splendid work with the diagnosis and the story.!! 👏🏼👏🏼👏🏼