Help Please. 02 trailblazer no crank, no start

Jeffreya97

New Member
2002 trailblazer ls 4.2l. Was driving fine until 2 days ago. Out of nowhere it doesn't crank. Luckily at the shop. I now of the common ignition switch problem. Replaced that about 2 years ago right after I installed a remote starter. During that install I actually soldered the wires in. Scotchclips are great at first but not for long term. Voltages at ignition switch: Brown-accy and run, Red/W all four, Pink-run and start, Yellow-start, White-accy, run and start, Red-all four, Orange-accy and run. By the power distribution diagram orange should only have run, I think the diagram is incorrect because it powers up the HVAC system which should work in accy position. Anyway I blew 30 bucks and got a new switch. Same result. I don't have a TECH2 so I can't see the crank parameter on my MODIS. Also cannot see the starter relay enable parameter. Backprobing at the pcm i get battery voltage ppl pin 31 while turning ignition to start. I have battery voltage at dk grn pin 29 in run and start. Same at yel/blk pin 48, run and start. Those are on connector 1. On connector 2 I have zero ohms at pin 65. No voltage drop from pin 65 to ground terminal of the battery either. If I manually ground pin 48 the car will crank and start but dies within a second and flashes the security light. Turning off the key resets this and no security light flash when attempting to crank again
I hate condemning pcms but I think it has all it needs to crank. I grabbed a pcm and bcm from an 02 envoy at the local yard. My assumption is that the passlock system works through the bcm. I swapped them in and the exact same result, however now the door locks unlock when I remove the key with the replacement bcm. they did not and still do not with the original if I swap back. My MODIS reads the different vin number and only throws a bcm code for the solar sensor. I have manual HVAC. I'll assume the envoy had automatic.
Are there any other modules that store the vin that could be affecting the VTD system and not allowing the pcm to give the crank relay ground signal? I dont think I have the immobilizer system. Can't find info on where to look for the module if I do. One last thing, I replaced the pcm with a programmed reman about a year ago to solve a throttle control issue.
Also wanted to add that when I try to start with the remote starter I get the same results.
 
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MRRSM

Lifetime VIP Supporter
Welcome to GMT Nation...

You can Help Yourself right away... by Downloading a GM OEM Digital Service Manual (Courtesy @Mooseman) for your particular Year/Make/Model SUV via the Link below. All of the Diagnostic Flow Charts are therein... Chapter and Verse for "No Crank No Start" investigations.


These Two Videos from @MAY03LT cover the "Cranks... No Start" and the "No Crank- No Start" problems...and you can use the attached Schematics to follow along with his approach to sorting out "The Baby from The Bath Water":



Fuel Pump Problem Diagnostics for Circuit Integrity and Fuel Pressure:


You've already looked at and repaired the apparent Ignition Switch problem... But by getting the chance to have a "Look-See" at Eric "O"'s "No Crank- No Start" Diagnosis... You'll have a chance to "Double Check" your wiring and soldering under the Steering Column again:


And to help you to have a "One Over The World View" of the Ignition and Fuel Systems Layouts... I'm attaching Three Diagrams for you to refer to. Before you Chamber any Rounds in the "Replacement Parts Howitzer"... Arming yourself with some additional Diagnostic Tools and the Patience to Poke around the Fuses and Relays in BOTH the Front Under-The-Hood- PDC (Power Distribution Center) AND the Under-The-Left-Rear-Seat BCM Fuse and Relay Box might also reveal more issues that can narrow the problem(s) down:

(1) A Freshly, Fully Charged Battery.
(2) A "Scope On A Rope" Lighted Continuity Probe
(3) A Decent Digital Multi-Meter to augment the use of your MODIS.
(4) "Hitting The Books" after you Download your Particular GM OEM Service Manual.

IGNITIONSTARTERCIRCUIT.gifTRAILBLAZERFUELPUMP.gifTRAILBLAZERFUELPUMP1.gif

You more than most of the Welcome New Arrivals who wisely venture to Join GMT Nation have the Talent and the Mechanic's Diagnostic Skill Set to get this problem solved. There are MANY MORE Experienced GMT Members here who are more than willing to Help you as you attack these issues and sort them out. So... Welcome Aboard, Brother!

PS

One Last Thought.... Whenever anyone mentions the expression "After-market Remote Starter" in the same Breath as " The Engine Won't Start"... THAT additional Non-OEM Equipment is always the First Thing To Look AT ...with a Jaundiced Eye.


Most of the Electrical Hook-Ups will have somehow interrupted things to the Extent of Making the Starting Circuit malfunction. So if you can Identify the After-Market System and Download and Link the Installation PDF for it to your Follow-On Posts... it will help guide the Members with experience in trouble-shooting such problems as to where to look for Suspicious Wiring.

The Final Suggestion I can make is this:

"Good Scientific Problem Solving Demands that You ONLY Change One Variable At A Time..."

If you get into the actions of Mixing and Matching PCMs along the way while ALSO changing ANY other system components In & Out ... it will make the process of getting down to the essence of the matter so much harder to do.

For ALL Trouble Codes... Take the PXXX Code issues IN THE ORDER THEY APPEAR and be as systematic as you can about bringing each one under control. The proper results from this Discipline will be that you'll get your Vehicle Up And Running MUCH Sooner than later.
 

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Jeffreya97

New Member
Thanks for the reply. Nothing yet on my end. Its been a busy week. Ill get back to the old TB tomorrow if I can. Ill let you know.
 

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