08 Suburban LTZ no start

Colín Edward · June 3, 2018

The vehicle has intermittent no crank / no start issues, displaying:

Service Stabilitrak

Service 4 Wheel Drive

Service ABS

Service Traction Control

Service Suspension

Park Assist Off

Most times it will go away if I poke around under the dash with my left foot.

I’ve replaced the positive and negative battery cables, with mega fuse, and had my battery and alternator tested.

The other day, I also noticed that it started shifting hard going from 1st to 2nd. It may or may not be unrelated.

i’ve attached a OBDII scan log. The HVAC code was because I had disconnected the A/C control module while installing a new radio.

Thanks in advance for your help!

Scan-Jun_03_2018_11-54-12-AM.pdf

update: I opened up the BCM and the solder joints look great. The conformal coating is still in tact. There were 2 large 220 uF caps that looked good. No internal relays to speak of. In previous generations, the relay solder joints seemed to be the weak points. Next I need to look st the PCM and TCM.

Edited June 4, 2018 by Colín Edward

Justin101714 · June 5, 2018

Any voltage on your purple signal wire at the starter when the problem is present? During those years a replaced a bunch of under hood fuse blocks and ECM’s for a no crank/ no start condition.

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Colín Edward · June 5, 2018

1 hour ago, Justin101714 said:

Any voltage on your purple signal wire at the starter when the problem is present? During those years a replaced a bunch of under hood fuse blocks and ECM’s for a no crank/ no start condition.

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Great question. I’ll definitely check next time I see the problem. I was hoping to take apart and inspect the fuse block to look into the internal relays needing to be replaced. There are a couple of cut wire harnesses under the hood and one under the dash that I’m hoping are aftermarket.

Edited June 5, 2018 by Colín Edward

Colín Edward · June 5, 2018

Also, a pair of red wires with ring terminals that are tucked back and wrapped to their looms under the hood. The terminals are corroded and I don’t see any voltage above transient.

Tahoe02 · June 5, 2018

How old is the battery?

Colín Edward · June 5, 2018

Just now, Tahoe02 said:

How old is the battery?

I’m not entirely sure. I bought the car in April. It’s an Interstate battery rated at 730 CCA and the battery checker showed it producing over 900 CCA. The machine also said the alternator and starter were good with very little AC ripple on the alternator. I was originally going to replace it but when the car gets in its no start phase, it can’t be jump started either. Twice, removing the battery and charging it all the way fixed the issue but it was over the span of hours to a full day. I would love for it to be the battery or alternator, not the ECM or fuse box.

Tahoe02 · June 5, 2018

I know if you have a bad cell or a cell going bad it can cause weird issues. Not saying yours is bad just something to consider. Not even sure if there is a test for that and may not show up on conventinal test equipment.

Colín Edward · June 5, 2018

8 minutes ago, Tahoe02 said:

I know if you have a bad cell or a cell going bad it can cause weird issues. Not saying yours is bad just something to consider. Not even sure if there is a test for that and may not show up on conventinal test equipment.

The no jumpstart thing is what has me thinking it’s not a battery, alternator, or starter issue.

Colín Edward · June 5, 2018

12 hours ago, Justin101714 said:

Any voltage on your purple signal wire at the starter when the problem is present? During those years a replaced a bunch of under hood fuse blocks and ECM’s for a no crank/ no start condition.

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Did the cars you fix ever die while driving? Mine is rock solid (save for hard shifting twice) while driving. No radio, window, or gauge cluster problems.

Justin101714 · June 5, 2018

No DTC’s setting in the ECM?

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Colín Edward · June 5, 2018

25 minutes ago, Justin101714 said:

No DTC’s setting in the ECM?

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None right now. The lost communications with body/transfer case control modules message comes up periodically. I drove it 17 miles and they came up during that time, but only found them using the OBDII scanner, not on the dash.

Justin101714 · June 5, 2018

Okay, you’re going to need find out what power mode data in the BCM looks like when the fault occurs. The BCM may be showing the ignition key off when the fault occurs and the vehicle thinks you physically turned the key off. You could either have a power molding BCM problem or an ignition switch problem or the wires in between the two. That what it sounds like to me.

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Colín Edward · June 5, 2018

36 minutes ago, Justin101714 said:

Okay, you’re going to need find out what power mode data in the BCM looks like when the fault occurs. The BCM may be showing the ignition key off when the fault occurs and the vehicle thinks you physically turned the key off. You could either have a power molding BCM problem or an ignition switch problem or the wires in between the two. That what it sounds like to me.

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Thank you so much for the help. Any recommendations on an affordable scanner to view the BCM data? My other vehicles are Honda’s and I have the Honda Diagnostics system. Do I need a GM Tech II? Is there a better tool for the price?

Justin101714 · June 5, 2018

You would need a tech2 or any reputable pricey scan tool to view that data. But first, when the vehicle exhibits the problem, do all the dash lights turn off too, like you turn off the key?

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Ferrnt · June 5, 2018

I once had a battery in my old "Found On Road Dead" 150 that cranked the car, played the radio, turned the lights on... did everything it was supposed to do. Couldn't even jump start it using my jumper or another vehicle. After replacing many parts trying to figure out what was wrong, took the battery in to get it checked. Dead Cell. Replaced the battery and she fired right up. Sold it shortly after. She didn't respond well to having 100amps sent through the system from the jumper for an extended period of time.

Good Luck

Colín Edward · June 5, 2018

2 hours ago, Justin101714 said:

You would need a tech2 or any reputable pricey scan tool to view that data. But first, when the vehicle exhibits the problem, do all the dash lights turn off too, like you turn off the key?

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The dash is totally normal with the key in “Run”, except for the service messages. Turn the key to start and the dash goes dark, except for maybe one or two lights. I need to pay closer attention to see which lights stay on when the dash goes dark.