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Did he verify that the relay was being turned on? Could you hear it click? And did he check voltage at any of the other fuses powered by the powertrain relay?
 

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Did he verify that the relay was being turn on? Could you hear it click? And did he check voltage at any of the other fuses powered by the powertrain relay?
I didn't know enough about the circuit to ask him if he could hear the relay turn on. But I did swap starter relay and powertrain relay and got truck to start about five times in a row before it quit again.

I then bought a new relay and swapped it around between the two positions and no start.

I can't say if he checked the voltages at any of the other fuses powered by the powertrain relay, but I believe it was checked.

Something to note is that the truck does run using a jumper from an unused circuit in the fuse box to fuse 23, ETC fuse. But it throws P0690 under these conditions
 

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Was the IGN off when you inserted the jumper? If so, that is why P0690 sets. With the IGN off, the powertrain relay is off so there should be no voltage at the IGN 1 ECM circuit. When you inserted the jumper, it immediately put 12v on the circuit. The ECM detected voltage on the circuit while the powertrain relay was commanded off and set P0690, so that is no big deal. But that pretty much confirms that there is a disconnect between pin 87 of the powertrain relay and the ETC fuse which would be due to a broken trace in the fuse block.
 
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Was the IGN off when you inserted the jumper? If so, that is why P0690 sets. With the IGN off, the powertrain relay is off so there should be no voltage at the IGN 1 ECM circuit. When you inserted the jumper, it immediately put 12v on the circuit. The ECM detected voltage on the circuit while the powertrain relay was commanded off and set P0690, so that is no big deal. But that pretty much confirms that there is a disconnect between pin 87 of the powertrain relay and the ETC fuse which would be from a broken trace in the fuse block.
Thanks dude.:coolthumb:
 

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No problem
 

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To the OP:

The first thing you need to do is get your truck back in a state to where it won't start. While it won't start, turn the IGN to run and test for voltage at the following fuses at the underhood fuse block:

#23, ETC, 15A
#31, INJA, 20A
#56, INJB, 20A
#26, ENG1, 15A
#55, O2 SNSR A, 10A
#54, O2 SNSR B, 10A

There should be two small holes on the top of each fuse that you can touch a probe to in order to test the fuse while it is still inserted into the fuse block. Use a volt meter and not a test light. Report back the voltages you get for each fuse and we'll go from there.
 

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If he troubleshoots it appropriately as i instruct him to, he won't have to guess, he will know.
 
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My point is not to just jump to conclusions and rip out the fuse block and tear it apart without first doing some troubleshooting to determine that the fuse block is indeed the problem. I do agree that it most likely is the fuse block but it may very well not be. A few simple tests with a multimeter can determine that. If tests determine that it's bad, then by all means rip it out and try to fix it, but if tests determine its not the fuse block, then he just saved the time and effort of unneccesarily pulling the fuse block out and tearing it apart.
 

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2006 white 2wd
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My point is not to just jump to conclusions and rip out the fuse block and tear it apart without first doing some troubleshooting to determine that the fuse block is indeed the problem. I do agree that it most likely is the fuse block but it may very well not be. A few simple tests with a multimeter can determine that. If tests determine that it's bad, then by all means rip it out and try to fix it, but if tests determine its not the fuse block, then he just saved the time and effort of unneccesarily pulling the fuse block out and tearing it apart.
I agree with you completed and your testing process should be followed by the OP! If the OP does find out his fusebox is bad, he will already have a head start on where to look so don't jump on someone for giving their 2 cents when they are just trying to help.
 

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Repair that one and keep it as a backup for when your new one does the same thing lol
 

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2008 TrailblazerSS
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Congrats on the fix


Sent from my iPhone using Tapatalk
 

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2007 RWD TVS 1900, E85, TL headers,
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To the OP:

The first thing you need to do is get your truck back in a state to where it won't start. While it won't start, turn the IGN to run and test for voltage at the following fuses at the underhood fuse block:

#23, ETC, 15A
#31, INJA, 20A
#56, INJB, 20A
#26, ENG1, 15A
#55, O2 SNSR A, 10A
#54, O2 SNSR B, 10A

There should be two small holes on the top of each fuse that you can touch a probe to in order to test the fuse while it is still inserted into the fuse block. Use a volt meter and not a test light. Report back the voltages you get for each fuse and we'll go from there.
I know this is old but hopefully it helps someone.
Without reading this thread I replaced the ignition switch. Pulled the fuse box apart, which looked amazing. Checked fuel pressure, grounds, ect.
I’ve been trying to figure out the same issue and found this thread so I checked all those fuses #23, 31, 56, 26, 55, 54 when the truck wouldn’t start. All were completely dead. Other fuses in the box had power. Later the same day the truck started and all the fuses had power again.
Is it safe to assume the computer is not commanding power to any of the ignition circuits? I have the original computer from the car and plan to put it in tomorrow and load the current tune into it. Any advice before then would be appreciated. Otherwise I’ll chime back in and let everyone know what happens.
 

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Just based off what you are saying, it sounds like your fuse block to me. I doubt it is your ecm. The ecm receives ign voltage from the ign switch. The ecm then applies ground to the coil of the powertrain relay. The powertrain relay supplies voltage to those fuses. What typically happens is the wire in the fuse block that goes from the powertrain relay to those fuses breaks, preventing the voltage from reaching the fuses. It typically breaks in the same spot and sometimes can be very difficult to spot. Pull your fuse block back apart and check the spot in the picture. A quick test you can do next time it doesnt run is, again, with the ign in RUN, verify that there is no voltage at the fuses mentioned previously, pull the powertrain relay out. Look on the relay and locate where pins 30 and 87 go into the fuse block. With a test light or multimeter, probe those two positions in the fuse block. One should read 12v and the other should not. Now insert a jumper into those two spots and then go check those fuses to see if you now have voltage there. If there is no voltage at the fuses it is most certainly the fuse block
 

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So I ordered a used fuse box off of eBay. I decided to take it apart before installing. Turns out it had a broke trace in it. Solder it and the car runs perfect again. Took apart the original fuse box and it also had a break in the exact same spot. Thank you for the help.
 
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