[Flyinfool]

The title says it all.
I have a P0650 indicator lamp (MIL) control circuit malfunction. I only found this because I failed my emissions test due to this code being present. The research I have done says that it meas that the ECM is sensing the the MIL (Check Engine Light) in a state other than the commanded state for more than 5 seconds. This could mean that the light is on when commanded to be off or it is off when commanded to be on.
My case is the MIL never lights, When I start the truck and it does the bulb check the MIL does not light.
According to the service manual it is one of 3 things, A bad instrument cluster, a bad ECM or a bad wire between the 2.
I believe the MIL is an LED so not likely burned out and the 2 other issues also point to something other than a bad bulb.

I can not renew my plates till I get thru emissions testing.

Details
1. The compass and the indicator for the cruise control are also intermittent, not working at the moment, and use the same circuit from the ECM to the instrument cluster. I believe that the MIL is on the same data line.

2. When the compass and cruise indicator work or don't work they always both have the same state.

3. What ever state the cruise indicator and compass are in when I first start the truck they always remain in that state for that entire drive cycle.

I am hoping that I can get this fixed this week, next week I go in for surgery and will be laid up for 3-6 months, but will need the truck to get around. I hate to take it to a stealer as I just know it will be the most expensive part possible.

 

[RayVoy]

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?

 

[brian c lindsey]

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

 

[Flyinfool]

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.....

 

[kennythewelder]

Good luck, let us know what you find.

 

[brian c lindsey]

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

 

[RayVoy]

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.

 

[Flyinfool]

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.

 

[RayVoy]

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.

 

[Flyinfool]

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.

 

[Flyinfool]

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.

 

[RayVoy]

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.

 

[Flyinfool]

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.

 

[Flyinfool]

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.

 

[Flyinfool]

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.

 

[RayVoy]

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

 

[Flyinfool]

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

 

[Flyinfool]

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

 

[RayVoy]

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.

 

[Flyinfool]

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.