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2002 chevy trailblazer_ls
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Discussion Starter #1
Had some trouble with the front differential so had the entire front drivetrain out of the vehicle including the oil pan. Put it all back together and got in to start it after being down for two months (charged the battery first). Nothing. Dash lights go out when I turn to start and back on when released to run. Checked starter and starter relay, good. Engines turns with starter (using bypass switch) so know it is good. Checked fuses, found PCM fuse blown, replaced, blows as soon as key turned to on, don't even have to turn to start.

Only wiring that was disturbed while apart is the 4x4 disconnect on the right side and the oil level sensor. There is one knock sensor that is bad but not removed from the system yet.

PCM is at rework shop and will be back in a few days but in the mean time I wanted to pick some brains for any tidbits of what to look for in case it isn't just a fluke and there is something else I missed.
 

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2002 gmc envoy_slt
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8 Posts
Check the TBC2 fuse under the back seat. That should control all dash lighting.
 

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2002 chevy trailblazer_ls
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Discussion Starter #3 (Edited)
Dash lights

Maybe I didn't explain my dilemma. The vehicle will not start/turn over. All that happens when the key is turned to "start" is the dash lights go out AND they come back on when key released to "run", which is normal operation EXCEPT the engine should turn over and attempt to start in the "start" position. Additionally when the key is turned from "off" to "run", the PCM fuse blows, as in, as soon as power is applied.
 

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2002 gmc envoy_slt
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8 Posts
Check for resistance on that wiring harness. That honestly sounds like a short to ground.
 

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2002 chevy trailblazer_ls
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Discussion Starter #5 (Edited)
Sometimes

As an electronics tech of 20+ years, I really like diagrams that actually show where each and every wire connects and the "signal" on each wire or at least the "flow" through the box/system. The diagrams in the Chiltons book is too cryptic and the PCM pinouts off this site don't help much either. Neither show the flow through the PCM.

Fuse 28. What does this feed that could be outside the PCM and shorted out? PCM MUST be in the circuit or fuse does not blow. Fuse 28 feeds the PCM in the pin that goes to Ignition 1, Fuse 23 aslo feeds Ignition 1 (could be Ignition 0, sources conflict) but it is not blowing. Both wires are pink, one goes in pin 19 the other pin 21 of BLUE plug. That tells me nothing. Where does this current come out at? What does it feed that could be bad and causing the short? Removing the blue plug stops the fuse blowing but also disconnects anything that connects the pins.

Do I have to buy a membership in AllData just to see if they have the wiring diagram to the PCM? Because if I can't get a good anwer from this site, one that doesn't send me on wild goose chases, then I'm going to be out thirty bucks just to find out that AllData probably doesn't have the diagram I need. Chiltons sure doesn't and so far no one has posted one on the web that even shows how power gets to the spark plugs.....
 

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2002 chevy trailblazer_lt_ext
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62 Posts
Have you checked that you did'nt pinch a wire/harness anywhere, when you reassembled everything? Just a thought.
 

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2002 chevy trailblazer_ls
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Discussion Starter #7
Pinched wires

Good point but no joy, for me anyway. One of the first things I looked for but there aren't many wires that can get in the way and they are all free and clear. All systems I can test without the PCM work fine.
 

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2002 chevy trailblazer_ls
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Discussion Starter #9
Another stab in the dark, are all the grounds clean and connected?
Vehicle was running fine when I drove it into the driveway to repair the differential. Only work done on it was to front drive train and charging the battery due to long down time. All grounds are good. Can make engine turn over (but not start) by bypassing start relay in fuse box, same with fuel pump and other systems accessible from there by applying ground or 12vdc where applicable.

Without a good wiring diagram showing me what the PCM is putting out to where on ALL wires, I'm at a loss of what to try other than dragging it to the Chevy dealer or selling it for scrap since I can't afford to pay their rates. (retired and disabled so money is TIGHT)
 

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2002 chevy trailblazer_lt_ext
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I'm going to try to attach a wireing diagram. It may or may not work. Its to big.
Whats your email and I will try to email it to you. Its 10.5 mb.
 

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2002 chevy trailblazer_ls
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Discussion Starter #12
Solved

Finally got Trailblazer to start!!! Believe it or not the culprit was the starter relay socket not making good contact with the starter relay in the under hood fuse box.

Relay checked good out of the vehicle, voltage checks to the socket pins checked good but when realy was in circuit fuse 27 would blow, sometimes. Was everytime but eventually got to where it didn't blow, suppose current was being drawn in directions it wasn't intended to flow. Some engineer didn't do a very good job foolproofing the circuit.

Still have some issues that were not there before this all happened but believe they are fixable once I locate area they are in. Oil pressure keeps going to zero (plenty of oil) and have to restart engine to get reading back. Radio doesn't play through speakers anymore. Neither of these were an issue before the vehicle sat for two plus months.

:duh:

Thanks!:eek:fftopic:
 

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2002 chevy trailblazer_ls
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Discussion Starter #14
Yeah it's full of oil and a new sending unit is soon to be installed, old one was leaking a few drops a month anyway but until the vehicle was down for a couple of months this issue was not there. Never thought parking a vehicle for a few weeks would cause so many problems.

I've parked one before for two years before and after repairing the dropped valve (why I parked it) it acutally started up without jumping or charging the battery!!!! Those were the days, vehicles that could sit and survive for months without constant maintenance. Pre 1970's models beat the crap for dependability out of these plastic and tin new ones.

Was a 1969, Olds 442 with a 455, 4spd, posi and lots of miles on it. After valve dropped had it towed and stowed while I spent the next couple of years overseas and had to fix it to get home on leave.
 

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I'm going to try to attach a wireing diagram. It may or may not work. Its to big.
Whats your email and I will try to email it to you. Its 10.5 mb.
Could you email me a wiring diagram? I'm having more of problem with transmission not shifting out of first gear. something isn't telling the transmission to shift.
 
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