Hey all, been having an issue I was hoping someone could help with.

2008 suburban 1500 LT 5.3 - been having the issue where the instrument cluster dies, gauges reset to 0, and all warning lights come on. This happens so frequently that I can rarely tell my speed. More recently, the IC has been completely freezing up, gauges stuck right where they are when it happens, DIC and shifter is blank, and cruise control cuts out. Also, my mileage doesnt go up when the IC freezes.

Decided to replace the battery cables to try to fix it... After reconnecting everything, I go to crank it up and nothing happens. Not even a solenoid click. All electrical is working fine, lights, radio, power seats, etc. But no start.

Climb under, check starter cable that I had just replaced and notice the starter case is cracked. Oops? Replace the starter... still nothing

Begin pulling fuses, nothing burnt out

Clean grounds on cables I just replace and check for continuity, all good. Check starter cable for power, reads the same as battery voltage.

Jumper starter relay, car cranks!! Swap relays around... no change.

Figure it must be the ignition switch.... swap it out, nothing

Noticed on instrument cluster that the shifter's location is not indicated under the transmission letters. Normally there's a line under whatever gear the car is in.

Decided to replace BCM - got my old BCM cloned to a used BCM by a locksmith buddy of mine. Plugged it in, all good except for it still doesnt want to crank! Still no line under gears. Also just now noticed the rear gate and glass don't want to open, although the rear wiper and sprayer do work. Not sure whats up with that.

No vehicle anti theft system light on dash. Still tried leaving key in 10 min, then crank. Tried leaving key in 10 min, then off x3 and nothing. Tried locking/unlocking with fob, key on, off, on again. So many different combos, all nothing.


Oh, and my instrument cluster? still going crazy. lol fml

any suggestions??

 

First, don’t replace parts/modules at random in hopes of fixing the problem. If you still have it, I’d recommend reinstalling the old BCM.

The cluster problem is secondary at this point - it can be unplugged and you should still be able to start and drive the suburban. If you want to make sure it’s not interfering, unplug it.

The correct procedure for the security system is to turn the key to CRANK, then leave it in the ON/RUN position for 10 minutes until the security indicator goes out. Considering the cluster is malfunctioning, it could be that the indicator just isn’t turning on when it should be; and I wouldn’t depending on it to complete the relearn at this point.

You need to pull diagnostic codes, but considering everything you’ve done at this point, I’d recommend a hard reset first. Disconnect BOTH battery cables and use vice grips or jumper wire to connect them together for at least an hour. Then attempt to start it - when it still doesn’t crank, then pull codes BEFORE doing anything else.

The PCM is the only controller for the starter relay - if anything about the security or communication system is preventing the PCM from engaging the relay, a code should be stored after attempting to crank.

 

The ignition switch is an extremely common problem on these trucks, and for $20, I thought, hell, why not. BCM was the most common solution I found and most people who said the BCM ended up being the problem had similar issues (no start, no line under gear selection). There's simply no way for a garage mechanic to test the BCM as far as I could tell. T

Could be... I am going to switch instrument panels with another person to see if that fixes the issue (should have just done this originally, d'oh). Read elsewhere that heat/cooling cycles cause micro cracks somewhere on the IC computer that causes it to work during warmer months and not so well during cooler months, which was how mine was acting originally... Side note, during VATS reset procedure, the dash stayed fully powered and functional without any glitches for several minutes at a couple different points.... security lock light on dash never turned on.

Had battery cables disconnected for hours at a time, and did try connecting cables for like 30 sec or a minute at one point, but never an hour! When I first was trying to diagnose the no start, the truck through 31 codes... cleared them with a scanner without paying much mind in an attempt to potentially clear whatever code was causing no start issue. In hindsight, I should have made a note of all the codes it was throwing.


Thank you for your reply!!!

 

Yes, the ignition switch and the BCM are both common problems on these trucks.... along without about 5 dozen other things that followed the body switch in 2007 including water intrusion into connectors, wire harness chafing in several places, corroded and loose ground connections, fretting corrosion, and terminals getting pushed out of the connector bodies, just to name a few, and all of which could be responsible for the no start and cluster malfunctioning.

It’s your suburban so of course do as you see fit, but there are several possibilities for the issues you’re having, and considering the parts swapping hasn’t solved anything yet, I’m only suggesting it’s unreasonable to continue doing so.

Yes, thermal cycling can cause the solder joints in the cluster to go cold; but the malfunctioning you describe could also be the result of loose connections or a bad battery.

The reason for connecting the battery cables together is to allow current flow which will discharge the internal module backup batteries/capacitors and clear all learned/adaptive memory. How long it takes depends on what a module has for backup power, but I can tell you for sure that 30-60 seconds isn’t enough. Leaving the battery unhooked without touching the cables together can take days for the backup power to fade. In my experience, an hour is enough for most modules.

As for testing the BCM (or any module) - they can’t be tested directly (at least not without very specific equipment) - so the rule is to check the inputs and the outputs. This where a wiring diagram or connector pin out diagram are most useful.

You start by checking if the relevant signals are where they need to be. In this case, check for ground at pin 86 of the starter relay (or 85 because sometimes it’s flipped) when turning the key to crank - if it’s there, the PCM is attempting to start the engine. That would immediately rule out ALL of the security and communication circuits that could be affecting the PCM’s control of the relay, and focus diagnosis to the power supply side of the control circuit.

But if it’s not there, then you move on to all the things that could affect the PCM grounding the relay. This includes checking the control wire between the PCM and relay, the park/neutral safety switch input, the “OK to start” signal from the BCM (data feed) and all the power inputs (direct battery and ignition switch) and ground feeds for the PCM.

If you found the BCM wasn’t sending the “OK to start” signal, then you’d start looking at all the inputs the BCM needs in order to tell the PCM it’s OK to start the engine.

The direction diagnosis leads is heavily dependent on the results of each test, but the basic method is to start with what you know you should have and work back from there.