[wesxlvii]

I have a 2011 Colorado 3.7 Z71 that has recently starting having very weird issues. after starting up to go to work the other day, my cluster started showing seemingly random errors, shutting down and coming back on, and will sometimes shut off completely showing only check engine and passlock lights. When it is like this, the truck will not start.

In troublehsooting, I found my AC resistor, harness, and blower all needed to be changed out so I did that yesterday as well as cleaned the two splice packs mount points (even though they looked perfectly fine). Also added a second ground from the splice behind the battery to the same spot the battery negative mounts to the body. It ran fine for 30+ min in the driveway while I put back together the glove box and cleaned up all the tools, plus a quick trip around the neighborhood, and multiple start/stops after. I thought it was fixed, then it did all the same stuff this morning when I was trying leave for work this morning.

Other notes and things I've checked from posts similar but not quite the same errors and symptoms:
Disconnecting the battery for 10+ minutes seems to get it to run normally for one or two more restarts, then it has the same problems.
Also opened up the passenger side splice and no corrosion.
I've owned the truck since 2012 so I know there's likely not any weird mods, botched fixes, etc.
No CEL/DTC show up on OBD scanner.
Cluster Errors: Brakes, Traction Fault, stability system, something about fluid, and a couple others I can't remember

Here's a video of the errors and rebooting cluster. Side note, low tire / tpms errors are normal, I've been too lazy to get the bad sensor replaced.

 

[wesxlvii]

Update on this if anyone can help:
Truck will only give me the CEL, no security light anymore, still no codes. It does sound like the fuel pump runs for a second and normal under-the-hood sounds when turning the key to Run but nothing happens when trying to start. Battery is good and has been on the charger while it was disconnected.
I've tried:
leaving the battery disconnected for a few days
leaving the neg cable disconnected and jumpered to the to positive for a few days
recleaned the splice pack mounts and added dielectric grease.
disconnecting negative and grounding each pin individually on the BCM and harness
thinly brushed on dielectric grease on BCM and Harness with nylon brush as described in that one service bulletin
There was a small amount of water under the carpet on both sides but i've since pulled it up and dried it out.
ground under passenger seat is good.
tried security relearn by leaving key in Run position for 10+ min multiple times.

I guess, are there other things to check? I think I saw something about the ignition cylinder and aftermarket radio (which I do have, installed probably 2013) but I wasn't fully understanding what to check with those.

 

[spaddman]

leaving the neg cable disconnected and jumpered to the to positive for a few days

Shouldn't this be the other way around? Disconnect the positive cable to the battery and short it to the negative, or ground. I guess the effects would be the same either way......

 

[wesxlvii]

Shouldn't this be the other way around? Disconnect the positive cable to the battery and short it to the negative, or ground. I guess the effects would be the same either way......

I'm no electrical engineer but I would think it would have the same effect. I'll try it when I get home from work anyway. I'll try anything at this point.

 

[cart7881]

When operating normally, when the key is turned on, you should see the CEL, Seat Belt, Battery, ABS, Traction and Airbag lights in the Tach display. After a couple of seconds the lights should go off, except for the CEL and Seat Belt. In the Speedometer display there should be Brake, Shift, Security and Oil lights and three should go off leaving just the Security light on. So, prior to starting, there should be three lights on, The CEL, the Seat Belt and the Security light.

When the key is turned to start the Security light and the Seat Belt light should go off immediately and the CEL should go out as soon as the engine starts.

I can see, in the video, that the lights are not operating normally when the switch is in start position. What is happening with the lights when the switch is in the run (on) position?

Maybe try swapping the Run/Crank relay with the RAP relay.

 

[wesxlvii]

When operating normally, when the key is turned on, you should see the CEL, Seat Belt, Battery, ABS, Traction and Airbag lights in the Tach display. After a couple of seconds the lights should go off, except for the CEL and Seat Belt. In the Speedometer display there should be Brake, Shift, Security and Oil lights and three should go off leaving just the Security light on. So, prior to starting, there should be three lights on, The CEL, the Seat Belt and the Security light.

When the key is turned to start the Security light and the Seat Belt light should go off immediately and the CEL should go out as soon as the engine starts.

I can see, in the video, that the lights are not operating normally when the switch is in start position. What is happening with the lights when the switch is in the run (on) position?

Maybe try swapping the Run/Crank relay with the RAP relay.

In the video, the truck was actually running. I can't even get it to do that anymore though. Now I have just the CEL and no other lights, nothing else happens in cab when putting in key, turning to acc, run, or start. turning from ACC to RUN to do hear fuel pump kick on for second or two and the normal clicking under the hood (relays? injectors? idk). Turning from RUN to START does absolutely nothing; no sounds, lights.

I'll try to record a new video when I get home.

 

[cart7881]

You're going to need some test equipment. Do you have a test light or more preferable, a multimeter?

 

[wesxlvii]

You're going to need some test equipment. Do you have a test light or more preferable, a multimeter?

I do have a multimeter, and maybe a test light.
Do you have a diagram of what pins should show voltage or continuity to ground?

More info:
forgot to mention, all fuses were good.
headlights and key fob/power locks work.
Windows and radio do not work

here’s the video I took tonight.
Key in, nothing happens, not even chimes even though the door is open.
Acc, no change.
Run, CEL only but you can’t hear the fuel pump or anything else due to background noise.
Start, nothing happens

 

[cart7881]

You will need to access the ignition switch by removing the lower steering column cover. The ignition switch connector has five wires, all White with different color stripes. Disconnect the connector and check the terminal at the White/Black wire for battery voltage. Should be hot at all times. There should be a good ground source in the area.

If you have battery voltage at the White/Black wire reconnect the connector. Now you will need to backprobe the connector to get the other readings. If you don't have a backprobe, just get a needle or straight pin. Push the probe into the back of the connector close to the wire that you are probing until it contacts the terminal. Then connect your meter to the probe. With the key in the Accessory position you should get 12 volts at the White/Red wire. With the key in the Run/On position there should be 12 volts at the White/Green wire.

If you don't have battery voltage at the White/Black wire there is a problem in the wiring from the fuse box. If you have power at the White/Black wire, but not at one of the others (White/Red, White/Green), the issue is probably internal to the ignition switch.

 

[wesxlvii]

@cart7881 thank you for the detailed write up! Unfortunately, all 3 wires showed about 12.4 volts.

 

[cart7881]

Did you try swapping the Run/Crank relay with the RAP relay?

 

[wesxlvii]

Sorry, missed that yesterday. Just tried it, no change

 

[cart7881]

Okay, I will get back with you later today, hopefully with something new.

 

[cart7881]

Okay, you indicated that you have 12 volts output at the ignition switch White/Green wire. That power goes to the BCM. It appears that the BCM is not getting the 12 volts or is not responding. Check fuses TBC 10A, TRN/HAZRD REAR 15A, and TRN/HZRD FRT 15A.

 

[wesxlvii]

12+ volts on both sides of all three. Also checked continuity across each fuse for good measure and they had 0 resistance. starting to sound like a bad bcm?

 

[cart7881]

Well let's see if the 12 volts is getting to the BCM. Sending you a message.

 

[wesxlvii]

Been a while, here's an update. Cart7881 helped me do some troubleshooting leading to a likely bad BCM. Beginning of November, had a friend of a friend that's a mechanic hook up his expensive scan tool and check the BCM and data bus, he concluded it was a bad BCM and said he'd order one for me. Fast forward to a month ago. the BCM he ordered never showed up then he just stopped replying to me at all. Ordered a remanufactured BCM programmed to my VIN and mileage from modulemechanics.com and it is doing the same thing.

Current issue is the same as in the video on post #8. If anyone has any further ideas or recommendations, please let me know.

 

[cart7881]

Okay, I just took a couple of Excedrin.

Regarding your notes in Post #8:
1. With no key in the ignition, does the led flash on the front of the radio? With the key in Acc and the radio turned off, does the clock show? Control of the radio operation is the BCM, but there is battery power to the radio for the clock. If the radio is not working the chimes will not sound when the key is inserted.
2. When you first get in the truck and close the door, the dome light should be on. If you immediately insert the key in the ignition, the dome light should shut off.
3. The headlights and the remote door locking are controlled by the BCM, so it has some functions operating. However, both of those circuits are on the battery bus.
4. If you push the Hazard switch, do the exterior lights flash and the arrows in the cluster flash?

You have tested the power to the ignition switch. You found 12 volts from the ignition switch to the BCM. Need to check for other power sources at the BCM.
Using the pinout charts and with the key in On/Run;
In the Black connector verify that you have 12 volts at terminals B7 and B8. I think you already checked one of those. Those two wires are coming from the iognition switch.
In the Gray connector, backprobe and check for 12 volts at terminals B6 and B7. Those are power outputs to the ECM, Fuel Pump Module,TCM and Run/Crank relay. If you can't backprobe, check the terminals at the BCM with the connector off.

Depending on your findings, there are several more power sources to the BCM that may need to be checked.

 

[wesxlvii]

1. I have an aftermarket radio that was installed in like 2012/13ish. I do have orig radio I can put back if necessary
2. No dome light with refurb BCM. Yes, old one does have dome light
3. Parking and headlights work with switch for both BCM. Remote door locks work with old BCM but not new (expected until relearn fob on new BCM as I understand it)
4. Hazards flash, with cluster arrows, on old BCM, not on refurb*

black connector:
B5-8 all show 12v on both BCM with key in run
Both only 12v on B5 and 8 with key out

gray connector:
Slot 6 is unused, no wire/pin in connector and says so on wiring diagram
B7 and 8 have 12v with key on both BCM

*Side note, with refurb BCM connected, hazards and dome light will come on only one time for about 1 sec or 2 clicks of hazard randomly after connecting

Also, switching back to old BCM to retest dome light I had a situation I forgot about happening previously. The CEL and security light come on but also the AC blower. The odd thing is, the ac fan keeps running unless I disconnect battery or bcm. I just tried to recreate this but could not get it to happen again.

 

[cart7881]

Okay, my bad. I apologize for adding more crap to an already confusing issue. I had the connectors backward. 'Senior moments' are getting more frequent.

With the key in On/Run position you should have been looking for 12 volts at B7 and B8 in the Gray connector and 12 volts at B6 and B7 in the Black connector. What I'm trying to do is figure out where the power is getting lost. You verified power to and from the ignition switch. From there is goes to the BCM. Then the BCM supplies power to other circuits. The power out at B6 in the Black connector goes to the Run/Crank relay, which controls a lot of functions. There shouldn't be any power to the above terminals with the key out. If we can verify these circuits, we can check the other power inputs to the BCM.

For the time being, I would suggest troubleshooting with the old BCM. The findings look more reliable for it.

Regarding the radio. For troubleshooting purposes I think it would be a good idea to reinstall it. One of the problems you have is no cluster display. The lights that you see working now are wired to a circuit. The remainder of the cluster is controlled using the Serial Data Bus. The OEM radio is a component on the Serial Data Bus. Most aftermarket head units are installed with an adapter to retain the chimes. If there is a failure in that adapter it could drag down the Data Bus. Reinstalling the radio should remove the head unit it as suspect. Because the radio is a Data Bus component, I would install it rather than just disconnecting the head unit. I'm not placing any bets on an improvement after reinstalling the radio. Just trying to eliminate a possibility.

Remember the caution: Always remove the Black BCM connector first and reinstall it first. GM doesn't say why, but it might be the cause of the blower glitch.