Intermittent Dash Lights/Gauges to Zero

[mrrsm]

Thanks for the Compliments... "Occam's Razor" Indeed... and it may well apply here in explaining the difference between Why this Problem Rears its Ugly Head whenever SHE is "The Pilot" ...versus the absence of this issue whenever you slide into the Driver's Seat and "Start the SUV" by focusing right back on your clear minded observation about "The Ignition Switch":

I'll pose these Questions:

(1) How Many "Keys, Key Rings, Remotes and Heavy Gee Gaws" does she have 'Bird's Nested' together ...right along with the requisite SUV Ignition Key?

(2) How Many Keys does your "Spartan Key Chain" hold by comparison?

If hers is the Over-Populated One... The Sheer Weight of all those items that invariably Bounce and Gyrate around or Pendulum To and Fro with the ever-present Forces of Gravity, Centrifugal Force and Angular Momentum they have to handle during every sudden Start and Stop as well as when she makes Left and Right Hand Turns at speed ...COULD be just enough to Jostle the Ignition Key loose enough inside of the Lock-work ...to Make Mischief. :>)

 

[bfairweath]

She's just using the key and the FOB right now. There have been times in the past where there's been enough stuff hanging off the ignition switch to dangle on the driver's knee, but that was years ago. I seem to recall asking (telling) her to get all that stuff off her key ring because, again, ignition switches on Trailblazers are high failure items.

Still no dash lights....

 

[mrrsm]

This is quite a lengthy thread ...but page to Post #25 regarding Investigating the BCM:

SOLVED! - No Start, Multiple U1000 codes, Class 2 Serial Communication Problem

2005 Chevy Trailblazer LT, 2-Door, 4WD, I6 4.2L engine Won't start or turn over. No starter signal at starter relay but when jump relay will turn over but not start. No check engine light. All instrument light on when first to key on the go out except battery & gauge warning light stay on...

gmtnation.com

Also @TJBaker57 has a Post that shows good images of How to Clean the BCM Ribbon Cable... but I could not locate that Thread.

Attached are the PCM C1, C2 & C3 Connector Pin-Outs AND... The BCM Wiring Layout. Pay particular attention to the GROUNDS back there that attach to the Local Pillar-Post for having Good Connections:

 

[bfairweath]

Well...so much for Occum's Razor. Dash lights and gauge event happened today, and I actually witnessed it!

Here's what happened.

Wife reported the CEL came on last night. I started it this morning and scanned it with BlueDriver. Had a P0420 - Cat Efficiency. This is nothing new. I've been getting that off and on for the last six months. Wife got into the passenger seat and slammed the door. That seemed to kick off the event (the door slam, not my wife entering the vehicle). Dash lights came on, gauges dropped to zero immediately (as before, tach and speedo continued working). Since I had BlueDriver hooked up, I did a full system scan. It didn't have a problem communicating while the event was happening, telling me the Class 2 network was at least partially alive. Report I got is attached. We drove about a mile and the cluster came back to life (lights shut off, gauges started to read normal). The door chimes came on for about 15 seconds and then everything went back to normal. When we got to our destination, I did another full scan. That report is also attached.

I hate to start throwing more parts at this. It seems like I should try a different instrument cluster and/or a different BCM because those are the modules reporting codes. However, one of the posts that MRRSM had a TSB in it that said the culprit is rarely the module that is reporting the codes.

Any idea on where to go next? Almost seems like we have to keep driving it this way until whatever module is causing the problem completely fails. Then, I could actually troubleshoot it. Don't think the wife is going to accept that though.

 

[Mooseman]

Sounds like a module is misbehaving intermittently and killing the network. And since it happened just when the passenger door got slammed, I'd suspect the passenger door module. As a quick test, unplug it and see if it still happens. Just be aware that the window, electric door lock and mirror won't work. Another possibility is broken wiring to the door that's shorting out.

It could very well be the cluster since you did have the code for it before all the others showed up. If you have a u-pull yard nearby, grab one from there and swap it out. Shouldn't be too expensive.

Because it's an intermittent problem, you can't do the normal troubleshooting by pulling the main class 2 network comb and jumping to each module until you find the one that's pulling down the network.

 

[mrrsm]

I'm going to risk mentioning an unorthodox step by suggesting that you eventually Check ALL Grounds in the Engine Compartment before deciding that the IPC is "The Suspect Module". I'm also hinting that if there are any of the Grounds involving the Modules Communicating with the PCM and ANY other Ground that involved the Sensors communicating on the Class 2 Network, they just might be acting "A Little Too Jittery"...Just enough in fact that One or More of them might be occasionally Breaking Ground. Please ... Start with the Network Splice Pack Ground (SP-201) located on the Passenger Side of the Transmission Hump FIRST and then work you way through the others in the Engine Compartment.

@MAY03LT 's Video on THIS particular subject is VERY Edifying:

 

[bfairweath]

Start with the Network Splice Pack Ground (SP-201) located on the Passenger Side of the Transmission Hump FIRST and then work you way through the others in the Engine Compartment.

I got right after this one. Took off the bolt and sanded both sides. Nothing obviously wrong. I have cleaned off several of the grounds since this problem started happening. The only one I found (so far) that was really bad was the one on the frame right below the driver side passenger door. I cleaned that one weeks ago.

If you have a u-pull yard nearby, grab one from there and swap it out. Shouldn't be too expensive.

I don't know of any u-pulls close by, but there is a very large auto salvager. I'll check them out.
Wife reported the phenomenon happened again today as she was leaving work. Happened exactly as I described above, but no passenger door slam.

I'm almost glad it's happening more often. More chance to troubleshoot.

 

[bfairweath]

Just and update on this problem - it's not fixed. It's happened several times in the past few weeks. They have been very short failures and seem to happen shortly after starting the truck cold - except for one on Thursday night. We were on a half hour trip and the failure occurred after about 15 minutes. Dash gauges died and lights came on and stayed on for about five minutes. A new symptom occurred - the radio shut off. Everything came back when I pressed the brake to stop for a traffic light. Maybe that's a clue. I've attached the BlueDriver report. 29 codes (I can't say they were all from this incident. I hadn't done a scan for a couple of days). Notice the B-codes for backup lamp circuit failure and rear door lock failure. Those are interesting.

After everything came back when I pressed the brake pedal, the Security light stayed on. That's new too. When I got home, I shut off the truck and restarted it. The Security light stayed off.

Things I've done since last post - Checked and cleaned the b-pillar ground (I think I've hit every ground now), cleaned the ribbon cable and all connectors to the BCM with CRC contact cleaner.

The large auto salvage yard in my area has instrument clusters for $30. I've resisted the urge to go down that road because of how infrequently this is happening. If it keeps happening like the incident Thursday night, I might have to load up the parts cannon. I'd have to guess BCM at this point.

 

[mrrsm]

Interesting. Now I can't swear that what is happening on the Dash-Lights Radio intermittent On-Off is related to THIS location, but since BOTH inter-communicate with the BCM, I suppose anything is possible.

I'm showing what follows as an example for you to consider Checking out the Door Modules AND the "Through The Boot" Door Harnesses for any Shorts in the Wiring similar to what happened HERE with the Tail Gate.

Check out THESE images as representative of "Work-Hardened Wiring" that eventually parts in between the LGM Harness and the Powers-Grounds and Class 2 Network Wiring that feeds through the Tailgate Weather Grommet.

If you manage to find ANYTHING that looks either THIS Damaged or Short Circuited like this mess, at the very least, it will be fairly straightforward enough to Repair. Keep in mind that the Copper Wires CAN Break INSIDE of the Insulation there, so it behooves you to suspect (and Inspect) ANY and ALL of them at this point.

It is unfortunate that on the Class 2 Single Wire Network Design, ANY Module that either shorts the 5 Volt Reference Wire either to Ground OR to the 12 Volts DC feed can bring the entire Network to a Screeching Halt.

 

[Mooseman]

This link has some interesting info about U1301, which I think is the root cause of your issues:

U1301 Chevrolet: Code Meaning, Causes, Symptoms, & Tech Notes

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and

www.engine-codes.com

Basically, high voltage is being sent on the data line. This could be a bad module or a short on a data wire somewhere. When it happens, everything gets disconnected and go bonkers. The radio is likely shutting off because it gets a signal from the network to turn on. It will be difficult to pinpoint because it's intermittent. You might have to resort to disconnecting one module at a time for while and see if it goes away. Hopefully it's not a major one like the PCM or BCM.

@MRRSM 's idea to check the liftgate wiring is a good one as it's often a source of broken wires and may be shorting there.

If and when it does happen and you want to clear it, try turning the key to START even while running and driving. This usually resets most of the modules. I regularly do this when I get a Stabilitrak error caused by the SWPS.

 

[mrrsm]

One other thing comes to mind regarding this "Braking" Phenomena... Whenever @bfairweath's Wife get into the Driver's Seat... it is likely that she has to adjust the Seat Rack Position to bring her pedal access closer. And when applying the Brakes... her position AND the weight of the seat would naturally tilt a little forward too.

Perhaps the Seat Position Adjustment Switch and any Electrical Harnessing under or near the Driver's Seat Motors are Shorting Out at that moment and causing these Bizarre Electrical events.

The Lift Gate itself is also subject to this same "Law of Inertia" and because it is NOT really "Solid State", even when Latched and Closed... Since it can swing Forwards under Braking and Backwards under Acceleration on its Roof Hinges...it too could be allowing Loose, Separated Wiring to "Make and Break" Electrical Contact ...from time to time.

 

[bfairweath]

There's a picture of the wires on my lift gate in post #34. The orange wire had some cracking in the insulation, but I believe the continuity is good. Back then, Budwich was suggesting that I disconnect the LGM for a while and see if the problem goes away. I never really gave that a good shot. I think I'll go there next and give it a good week with the LGM disconnected.

My TB is an LS so no power seats. My wife and I drive with the seat in the same position. HOWEVER, my 15 year old with his learner's permit likes to move it way back. Come to think of it, this problem showed up very close to the same time he got his temps. I'll take a look under there. There's got to be some electrical connections even without power seats.

I don't really want to invest in a high end diagnostic tool specific to GM with this vehicle being in, shall we say, the sunset of it's life. Seems like I'm going to need something more advanced than BlueDriver, Torque, and a VOM meter. Maybe investing in an oscilloscope is the thing to do for inspecting the 0-7 volt Class 2 waveform at each node or the splice pack(s). I'll ask Santa for one.

 

[mrrsm]

As long as All Three Connectors come off the LGM. They SHARE Cross Wiring between them that can include the Class 2 Network 5 Volt Reference Wire and so if it happens to be Grounding out below that point... it could still interfere down the line with its "Earlier" feed in wire every time it decides to touch anything on the Body:


Food For Thought:

During an Autopsy of a Used eBay LGM I bought to tear apart and figure things out turned up with a Dead Short between the Plug carrying the 12 Volt DC into the LGM Logic Board where it is supposed to connect into the Flat Steel Tines and remain attached to the Logic Board. I note that all three Connectors have different Tine Sizes and All Three Sub-Wire Bundles come together further down in the Harness to share certain Wires from each one.

It had obviously been bouncing around uncountable times over the years due to all manner of Vehicle Vibrations and loosen enough to repeatedly Arc Electrically. After the Arcing managed to burn through the Cadmium Plating on the Tines, it succeeded in completely Melting Right Through the Plastic Connector Housing, charring the Wire Insulation and shorting out the Harness Plug. Performing a Tear Down and Inspection of the LGM and the Three Connectors is a very straightforward procedure and well worth doing under these suspicious conditions.

I've attached all of the Class 2 Network Diagrams for both sides of the System that will allow for tracing out the individual LGM Connector Wiring Pin-Outs by Color and Function as well as what the localized BCM Network Wiring looks like:

 

[mrrsm]

FWIW... One More Swing in The Dark...

Recently, @TJBaker57 pulled the BCM cable (Green-n-Gold Data Ribbon) off of the "Tesseract" under the Left Rear Passenger Seat and discovered what looked like "Congealed Coca Cola" along the Contact Points. After he cleaned the whole thing up and re-installed the Cable and Plug...the Network Comms Problem went away. It won't hurt to look at this one, too. :>)

 

[bfairweath]

Recently, @TJBaker57 pulled the BCM cable (Green-n-Gold Data Ribbon) off of the "Tesseract" under the Left Rear Passenger Seat and discovered what looked like "Congealed Coca Cola" along the Contact Points. After he cleaned the whole thing up and re-installed the Cable and Plug...the Network Comms Problem went away. It won't hurt to look at this one, too. :>)

I sprayed this area down about a week ago with CRC Contact Cleaner. I saw the same stuff. I was thinking 18 year old dialectric grease but maybe not. I'll take another look.

 

[TJBaker57]

I sprayed this area down about a week ago with CRC Contact Cleaner. I saw the same stuff. I was thinking 18 year old dialectric grease but maybe not. I'll take another look.

Wasn't my truck with the goop on the ribbon cable, but a fellow who I helped track down the issue somewhere online.

In any event it is fairly easy to take all that apart and even opening the plastic BCM case to check for any issues is super simple. Disconnect battery of course!

 

[bfairweath]

New clue - I just returned from a short trip. Did a couple of scans. Now there's a persistent C0291 code. This code was present in the list of 29 codes I posted earlier, but I didn't really catch it.

According to Engine Codes.com this is:

"The Body Control Module (BCM) sends a state of health serial data message to the Electronic Brake Control Module (EBCM) within 5.5 seconds after the ignition is turned ON. The EBCM fails to receive serial data from the BCM. "

The Brake Control Module is out in the elements under the vehicle and I am in the rust belt. I'll crawl under there and take a look at the wiring in the area and spray down with contact cleaner.

 

[bfairweath]

Update- the TB is still fighting for life. After my last post, I took the two plugs off the the EBCM and sprayed both sides with contact cleaner. They looked okay. Didn't look like there was any water/salt infiltration. However, I also took a closer look at the ground for the ECBM (right under the driver side door). I had "rebuilt" this ground point many years ago. I broke the bolt taking it apart and replaced it with a stainless nut and bolt with a stainless washer (washer between the frame and the ground wire). When I took it apart last week, there was a lot of corrosion under the washer. Could have been affecting the ground contact. I cleaned up the frame with a wire wheel and put it back together without the washer.

After doing all this work, I started it and scanned - no codes. Shut it off, started and scanned again - no codes. As I was standing there, wife came out to run an errand. She started it up and said "Do you know these lights are on?" Gotta be kidding. Did another scan and found three codes. - U1000 x 2 (class 2 data link malfuncition) and U1301 from the BCM (class 2 data link high. The lights shut off after about 10 seconds.

That's been the only incident in over a week. I'm hesitant to blame the EBCM ground point since there was one minor incident after I cleaned it up, but it hasn't gone a week without an incident in the recent past.