SOLVED! No Crank On 2002 Trailblazer 4.2

[ek02]

I went to drive my 2002 Trailblazer today and the remote would not unlock the doors. It also would not crank over. The battery tests good and if I jump the start relay it will crank but not stay running. The relay tested good. The ignition switch has power to the red wire, pink wire, and yellow wire in crank position. No codes present, but I do get a U1000 with my cheap scan tool, which I believe means no communication with the PCM. With the key on all lights work and go off except the check engine light. The door locks and power windows and radio will not work either. I got to the point in the service manual diagnostics where it said to check for power in the crank position at pin 31, purple wire, at the PCM blue connector. It had power in the crank position. It leads me to think the PCM is bad. Am I missing anything? Where can I get a PCM? I believe it has to be programmed if that is the problem. Strange that the door locks, windows, and radio will not work. Almost like a bad ground somewhere. Any idea where to check? The shop manual is not showing where the grounds are. The pin on the crank relay that is supposed to ground is not grounding in the crank position but the PCM is getting a crank signal, so that makes me think it's the PCM.

 

[mrrsm]

This is THE Will Robinson's Auto Signature Instructional Video that will show where the Class 2 Network Splice Packs (0-7 Volts DC) are located and EXACTLY How to Troubleshoot UXXXXX Codes on the Trailblazer and Envoy Platforms. Please... Be patient and watch the entire video for the helpful tips and the tools needed here:

Regarding the large number of Class 2 Network Ground Locations... @MAY03LT shows where the G101 and SP-201 Splice Pack are located and how to ensure a Good Ground:

...and here are his No Crank - No Start Videos:

And finally... if it comes down to cases and you REALLY need a Replacement 2002 Chevrolet Trailblazer PCM... there are many Used and New ones available on eBay via THIS Link:

https://www.ebay.com/sch/i.html?_fr...&_nkw=2002+chevrolet+trailblazer+pcm&_sacat=0

 

[mrrsm]

And for everyone... Here is the KISS Principle at work for something very easy to check and worth watching because this particular NO CRANK - NO START problem is often overlooked and VERY EZ to rectify:

 

[ek02]

Thanks for the videos. I went through them earlier and my conclusion is that pin # 31 in the blue PCM connector gets it's signal from the ignition switch. That pin has voltage. The PCM then grounds the start relay at pin 48. I need to ground pin 48 and see if the relay energizes. There is no ground at the relay when the key is turned to crank. I can get the engine to crank when I ground that pin with the relay semi inserted. I wish I had a Tech II to follow the diagnostics in the shop manual. I have found a lot of companies that have PCM's with the numbers I have on my PCM and will program them from the VIN. My volt gauge also reads 0. All other gauges are working. Seats, mirrors, all lights still work. Just door locks and windows don't work and all the buttons on the steering wheel are dead.

 

[TJBaker57]

Thanks for the videos. I went through them earlier and my conclusion is that pin # 31 in the blue PCM connector gets it's signal from the ignition switch. That pin has voltage. The PCM then grounds the start relay at pin 48. I need to ground pin 48 and see if the relay energizes. There is no ground at the relay when the key is turned to crank. I can get the engine to crank when I ground that pin with the relay semi inserted. I wish I had a Tech II to follow the diagnostics in the shop manual. I have found a lot of companies that have PCM's with the numbers I have on my PCM and will program them from the VIN. My volt gauge also reads 0. All other gauges are working. Seats, mirrors, all lights still work. Just door locks and windows don't work and all the buttons on the steering wheel are dead.

Have you downloaded from Moosemans links? Wiring diagrams are in there.

 

[gmcman]

Do you have an aftermarket security system?

 

[mrrsm]

Unless you already have them, these PCM Three Connector and BCM Pin-Out Diagrams might prove useful:

 

[ek02]

Do you have an aftermarket security system?

No aftermarket security sytem.

 

[ek02]

Thanks MRRSM. I have the pinout diagrams in the factory shop manuals. I disconnected the blue connector on the PCM and grounded pin 48 with the key on. The engine cranked, and since pin 31 had power with the key in the crank position, my no crank has to be the PCM. I found one here in town and will try to get it tomorrow. I hope it fixes all my other non working items. None of the other problems are controlled by the PCM, but it's possible the BCM can't function with out a good PCM. Looks like there are data lines from the PCM to the BCM. This TB has 146,000 miles on it but is in mint condition and in the family since new. It normally runs great.

 

[gmcman]

Was this a daily driver and just happened all of a sudden or did it sit for awhile?

I haven't looked at the schematics yet so not sure what gets powered from what, just throwing this out, but have you checked the large fuses at the front of the fusebox?

Have you removed the fuse box and and checked for any rodent damage to the wires under the fuse box?

 

[ek02]

This vehicle was driven daily. I came out in the morning to drive it and the remote would not work to unlock the doors and then it would not crank. Happened all of a sudden. I haven't removed the fuse box in the engine compartment yet, but all fuses are good at that box and the one under the rear seat. If the new PCM doesn't fix it then the panel will come out to check for damage.

 

[gmcman]

Wanted to add did you also check the 125A mega fuse?

 

[ek02]

Yes, it's good.

 

[ek02]

I tried a new PCM today and still no luck. I wonder if the BCM or theft deterrent system could have a problem? This all started when I went to unlock it with the remote and the door locks clicked weak and rapid. Then the no crank. I still get a U1000 on the scan tool. I can find BCM's on e bay with the same part number as mine but not sure that will work since most descriptions say they mount on the front fuse panel. Mine is under the rear seat.

 

[mrrsm]

@gmcman 's idea about searching for THESE artifacts of "Rodent Gnoshing" is a good one. Use a Bright Flashlight while examining the wiring bundles and connectors for damage, If you can see signs of nest building with Grass-Twigs and Headliner Material...use some CAUTION here. These are Real World GMT Member Images showing what to look for on the GMT-360s:



Please use a Face Mask and Gloves to avoid inhaling or handling desiccated Rat-Mouse Urine and Feces that the Common Deer Mouse transmits the Hanta Virus (..think 'Cousin to Ebola' here). THIS disease makes COVID look like a Hang Nail by comparison with their ultimate Kill Rates):



Even though Will from Will Robinson's Auto was uses the Highest End Scanning Tools and Oscilloscope possible to perform the Tests and Diagnostics mentioned in Post #2... It really is not necessary to have any of them.

You can simply locate those Two Class 2 Network Splice Packs both under the Dash-Driver's Side and under the Right Rear Passenger Seat and by a Process of Elimination... Turn the Ignition Key ON...Turn the Radio ON and after pulling loose the Plastic-Metal Comb, use the Grounding Colored Network Wire in each of them to methodically connect each Splice Pack Pin... one at a time and see which Module either brings the entire Network down or allows it to become active.

Using Back-Probe Pins will prevent damaging the Splice Pack Internal connections from the front of them. Will's Technique of using a few Safety Pins looks promising.

If you watch the Video at the key places where he shows his Snap-On Verus Screen... you'll have the chance to Freeze Frame & Screen Print the Splice Pack Wire connection Position, Color and Alpha-Numeric Identifiers ...so you'll know which Module you are checking in each position.

 

[budwich]

its less likely that a module "croaked"... more likely a wiring issue so replacing parts and not looking at electrical conditions at the components is probably not going to get a good result. Are the door locks still responding the same way? IF so, you should be looking at the LFTGM in terms of the wiring. Its a known area of failure.

 

[TJBaker57]

Exactly what sort lf "cheap scanner" are you using?

 

[ek02]

Its an Actron scan tool. I pulled the under hood fuse panel and there is no evidence of rodent activity. The door locks still don't work. What is the LFTGM budwich? Left door lock module?

 

[Blckshdw]

I believe he means, lift gate control module. That controls the locks

 

[ek02]

Got it. Thanks. I read a post that said a bad connection could cause the door locks not to work, but would that have any affect on the no start problem?

 

[budwich]

IF the module is fubarred because of connection issues, it may be babbling on the data bus which causes all sorts of problems.

 

[mrrsm]

Right ... and for the sake of a 'Quick Demo' ... watch this 30 Minute Video on how this problem can be remedied ...even though it happens on a different GM Truck Platform while the VOP uses the very same Procedures and Tests followed by Will Robinson.

Most importantly... he too relies upon a Tried and True "Trial and Error" Method to delve into each Module on the Class 2 Network, then Identify and Disable a completely FUBAR ABS Module that was making this Late Model Truck Dead as a Door Nail. After he unplugged it,, he was able to turn the ignition key and instantly get the truck to start up and run normally again.

Please... Take Note of all the New Parts yet to be Un-Boxed ...just laying up on the Dashboard,waiting to be Loaded into the "Parts Cannon" and Fired at this Vehicle! But Thankfully...the Hero of his Own Story finally saves the day (and the Truck Owner's Wallet) from all that unnecessary expense.

The VOP (Video Original Poster) here is THE Guy who taught Will Robinson how to do this very same type of Class 2 Network Failure Diagnosis:

 

[ek02]

Thanks, guys. I'll get back at it. The LFTGM makes sense since the whole thing started with unlocking it with the remote. I know where the splice packs are but without a Tech II I have no way to see what comes on line. I also was told to disconnect both battery terminals and touch them together. Not sure what the purpose is but it can't hurt.

 

[TJBaker57]

Tech II I have no way to see what comes on line.

This is why I asked about the scan tool. With one of these $12 bluetooth OBD adapters and a serial terminal app you can see everything that is on that data bus.

I think I'll go make a quick demo right now!

BRB

 

[mrrsm]

I would NOT recommend connecting the Positive and Negative Battery Leads together while as much as 600-700 Cold Cranking Amps surges in between and possibly destroys the Battery...and possibly harms you, too.

Adding to @TJBaker57's suggestion... The USB hard line to DLC Connector version of that same Scanner might be a better choice in this instance ...since the Blue Tooth version may not work at all on a 'scrabnoid' Class 2 Network. You also do NOT necessarily NEED a Tech 2 Scanner, Laptop or Tablet and a PICO (The $80.00 Hantek version is much more affordable) Oscilloscope. As shown in the attached video... try following the Splice Pack Wire Jumping Technique ...Testing each Module one at a time until you can see how the vehicle reacts with Ignition Key "ON".

For now... Leaving the Key in the ON Position during your Testing might allow that "Door Adjar Bong Tone" to alert you when anything changes, like the Dash Lights and Gauges on the IPC if they respond and wake up once the Steel Teeth Comb is removed. Make some notes from the Video about the Splice Pack Pin-Out ID Diagram so you'll know which particular Module went Bad by name.

 

[TJBaker57]

So just for demonstration purposes....

 

[budwich]

OP should also back up a bit before chasing things too far too fast as this started out with "because there was no ground provided by the PCM and that if he provided a ground on the appropriate pin, it would attempt a start", he "decided" that the PCM was bad and hence replaced it with no better result. That usually means that one has does nothing to help the problem... ie. the item was not the root problem.
However, there are some simple observations missing from the post... the main one is: what is displayed on the instrument panel when the key is just turned to "ON/RUN" (ie. not start attempt)? Some times a posted picture of the display will help with your "eyes" as then everyone will see what you are seeing or not seeing.

Edit:
Oops, I reread the first post and see that the PCM light is on with key ON... sorry for the "mis-direction"... please continue with the suggestions with focus on the tail gate wiring.

 

[TJBaker57]

Just an observation but.... Liftgate module wouldn't affect window operations of drivers door/window.

 

[ek02]

Any suggestions as to what type of OBD adapter for a blue tooth adapter and where to buy it? I have an I phone and an I pad if it will work on those devices. Also, the suggestion to touch the positive and negative battery terminals together for 10-15 minutes is with the LEADS REMOVED FROM THE BATTERY. Its supposed to reset the logic. Probably a waste of time. I will try to get the lift gate open today since i need to get some things out of the back. I'll also try the splice pack recommendation. It should be in the shop manual I hope.

 

[budwich]

you can't open your lift gate?

 

[Mooseman]

You can do a reset by just disconnecting the battery for 30 minutes. I wouldn't touch the two cables in case it causes a surge of some sort from the residual power in the various modules.

@TJBaker57 can confirm but I'm pretty sure you are SOL if you have Apple products as they lock out bluetooth functionality.

I'm thinking that the BCM is affected if NOTHING works. If it was just the LGM, the windows and such would work, especially at the module itself. The U1000 is saying a lot here. You will need a proper scan tool or a bluetooth adapter and an Android device to check the comms.

Check the BCM physically as we recently had one member have a damaged ribbon cable caused by a short from a liquid.

 

[ek02]

I was able to get the lift gate open and found the connector at the top of the lift gate. I unplugged it and plugged it back in and heard a click and the door locks started working. Still no crank but the security light came on and stayed on which it was not doing before. The radio also started to work. I went to get the passlock key programming directions and now it is the same as before. I thought for sure that was the problem. The wiring all looks good in the lift gate with the cover off. There may be another connector in the body that has a bad connection.

 

[budwich]

what does this mean... " went to get the passlock key programming directions and now it is the same as before" ? you went thru the programming and that turned off the security light but it still won't start? Is the radio working?

 

[TJBaker57]

So the iPhone/iPad thing does complicate matters and may not work out for this specific instance. As I understand it, iPhone users buy WiFi versions of these obd adapters and there are for certain iPhone apps for reading codes and the like. However, for hands-on communications on the SAE J1850VPW network a serial terminal application is needed and though I see there are such apps I have no personal experience with them or with apple products.

 

[Mooseman]

I think he means the security relearn.

@ek02 , What does the security light do?

 

[ek02]

I put the original PCM back in. The security light went off because PCM has the original key already programmed. I removed the ribbon connector on the BCM and it looked clean. When I put the ribbon connector back in, the doors sounded like they were locking with the remote but the L R door kept clicking for 10 seconds or so just like when this problem first started. Then I hit the key and it started, but no volt gauge although the battery was getting 13.5 volts. I turned it off and started it again and everything worked including the door locks, radio and steering wheel controls. I didn't try the windows. Started it a few times. Turned it off and all dead again. While it was running I got some codes out of it. C0291 parking brake relay open or shorted and U1064 loss of communication with BCM. When it acts up only the rear door locks will work. This thing is haunted. If it's the BCM does that have to be programmed?

 

[Blckshdw]

Hmm, so after you're able to get it started multiple times, and then it quits on you, are you able to "reboot" the cycle again by re-seating that BCM connector? Or does it stay dead for a while?

 

[ek02]

Different results every time I re-seat the connectors on the BCM. The door locks will work at times, then the radio, and the power windows worked one time after I did it while the door locks and radio were working. It will not crank again after it started 3 or 4 times. The left rear door lock continues to click about 10 times then stops when opened by the remote. Sometimes the horn blows after locking the doors until I turn the key on. Does anyone know if there is a ground for the BCM?

 

[Blckshdw]

Does anyone know if there is a ground for the BCM?

I'm pretty sure the BCM shares the ground that under that seat for the fuse block.

 

[TJBaker57]

Does anyone know if there is a ground for the BCM?