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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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02 Chevy trailblazer won't start I can ground to start relay

Customer Question

02 Chevy trailblazer won't start I can ground to start relay and when I turn the key to run the starter cranks the motor and I'm when I remove the wire The motor shuts off. I've also tried to other PCM's sign condition. I've also checked the neutral safety switch and the ignition switch which both seems to be working right
Submitted: 7 months ago.
Category: Chevy
Expert:  Dave Nova replied 7 months ago.
Do you have voltage at the CRANK fuse with the key in the Start position? This fuse is in the underhood fuse panel.
Customer: replied 7 months ago.
Yes it has power with the key off for the key on
Customer: replied 7 months ago.
my bad I was checking fuse 11. Fuse 17 crank fuse has power when key is in start position
Expert:  Dave Nova replied 7 months ago.
Did you say that PCM has been replaced?
Customer: replied 7 months ago.
Yes I got two used ones and both don't work
Customer: replied 7 months ago.
Like I said at first I can get it to crank and start by grounding the relay so I figured it wasn't grounding through the pcm but it should only work when the key is turned to start but it cranks when turned to run and that isn't right
Expert:  Dave Nova replied 7 months ago.
Starter relay has voltage with key in RUN position, so if you ground the relay it will engage in start or run positions. In rear fuse panel (under 2nd row seat, left side) check fuse 50, fuse 31 and fuse 52 for voltage with key ON. If you have voltage there, check voltage on fuse 22 in underhood fuse panel also with key ON. Let me know what you find there.
Customer: replied 7 months ago.
All those fuse check good with power to both sides. I should mention this problem started intermittent befor we changed all the shift solenoids in the tranny due to not up shifting to 3rd and no shift into 4th. After change the tranny still acted the same. So we opened the pan to check for ground out to each solenoid even though new wire harness was included in kit.
Expert:  Dave Nova replied 7 months ago.
The ignition switches in the Trailblazer are notorious for failing. This can cause loss of voltage to starting circuit, PCM, or even the transmission shift solenoids. I know you show voltage at the fuses, but once a load is placed on the circuit, the voltage may be dropping out. My suggestion is to go ahead and replace the ignition switch and see if this solves the problem.
Customer: replied 7 months ago.
Ok I'll try that but I just don't like to poke and hope that's why I came here to make sure. I though to do this but was hopeing you could prove it first
Expert:  Dave Nova replied 7 months ago.
I too dislike replacing parts without a definite diagnosis. In this instance it can be hard to get voltage to drop out without loading the circuit. The fact that the ignition switches in the Trailblazer are very prone to failure makes me believe this could be your problem.
Customer: replied 7 months ago.
I put a new switch no crank still.
Expert:  Dave Nova replied 7 months ago.
Do you have original PCM in place?
Expert:  Dave Nova replied 7 months ago.
Is Security light on or flashing when attempting to start?
Customer: replied 7 months ago.
Not original plan but I have it. No security light on when jet to run but goes out with all the lights.
Customer: replied 7 months ago.
Not original PCM
Customer: replied 7 months ago.
I put original PCM in with new ignition switch still no crank
Customer: replied 7 months ago.
Security light on when key turned on and goes out with all lights
Expert:  Dave Nova replied 7 months ago.
Try 30 minute relearn procedure shown below. If security light does not stay on in steps 2, 5, and 8 leave the key on for 10 full minutes regardless of light. 1. Insert a master key (black head) into the ignition switch.2. Turn key to the “ON” position without starting the engine. Security light should turn on andstay on.3. Wait for 10 minutes or until the security light turns off.4. Turn key to the “OFF” position for 5 seconds.5. Turn key to the “ON” position without starting the engine. Security light should turn on andstay on.6. Wait for 10 minutes or until the security light turns off.7. Turn key to the “OFF” position for 5 seconds.8. Turn key to the “ON” position without starting the engine. Security light should turn on andstay on.9. Wait for 10 minutes or until the security light turns off.10. Turn key to the “OFF” position. The key transponder information will be learned on the nextstart cycle.11. Start the vehicle. If the vehicle starts and runs normally, the relearn is complete. If additionalkeys need to be relearned:12. Turn the key to the “OFF” position.13. Insert the next key to be learned. Turn the key to the “ON” position within 10 seconds ofremoving the previously used key.14. Wait for security light to turn off. It should happen fairly quickly. You may not notice thelamp, as the transponder value will be learned immediately15. Repeat steps 12 through 14 for any additional keys
Customer: replied 7 months ago.
I did it still no crank
Customer: replied 7 months ago.
I tried this before with the same result.
Customer: replied 7 months ago.
I notice I'm getting no reading on the alt gauge but the battery is new
Expert:  Dave Nova replied 7 months ago.
Do you have a scan tool?
Customer: replied 7 months ago.
Yes snap on red brick
Expert:  Dave Nova replied 7 months ago.
Are there any modules that are not communicating with the scan tool? Any dtcs in any of the modules?
Customer: replied 7 months ago.
Shows code u1000 class 2 serial comm problem
Expert:  Dave Nova replied 7 months ago.
Which module is this code set in?
Customer: replied 7 months ago.
I'm not sure what you mean. I just checked with the scanner and it showed this code
Expert:  Dave Nova replied 7 months ago.
Do you have any other components that are inoperative (gauges, radio, door locks, lighting) ?
Customer: replied 7 months ago.
Yes some lights not working and the alt or battery gauge is not reading when key is on
Customer: replied 7 months ago.
Dome light not some
Expert:  Dave Nova replied 7 months ago.
Does the snapon communicate with BCM?
Customer: replied 7 months ago.
No
Expert:  Dave Nova replied 7 months ago.
Will it communicate with ABS module or instrument cluster?
Customer: replied 7 months ago.
No it only looks at engine or trans
Expert:  Dave Nova replied 7 months ago.
Sounds like the BCM (body control module) may not be operational. It controls security and lighting functions. Best to check power and ground to the module first (all fuses labeled TBC). Then try to communicate with the BCM with a more advanced scan tool. If there is no communication then the module has failed.
Customer: replied 7 months ago.
So what does the BCM have to do with the starting circuit ?
Expert:  Dave Nova replied 7 months ago.
The BCM controls security functions (alarm system, vehicle anti theft) so it can disable the starting circuit.
Customer: replied 7 months ago.
Ok I got a different BCM a dim doing the 30 min reset. I noticed that this is marked as closed. I didn't close it so did you cause the problem isn't fixed yet
Customer: replied 7 months ago.
And my scanner does communicate with the abs
Customer: replied 7 months ago.
Ok tried the security reset twice with new BCM still no crank
Expert:  Dave Nova replied 7 months ago.
I did not close the conversation, perhaps the website did. Was the new BCM programmed to the vehicle by the dealer?
Customer: replied 7 months ago.
No I got it off eBay and it has the same numbers on it
Expert:  Dave Nova replied 7 months ago.
The replacement BCM has to be programmed to the vehicle by the dealer or it will not work.
Customer: replied 7 months ago.
So the dealer has to have the whole truck or can I just take the BCM to them?
Expert:  Dave Nova replied 7 months ago.
The dealer needs the vehicle with the BCM installed to do the programming. They do not have an interface to program just the module.

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