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2005 chevy trailblazer_ls
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Discussion Starter #1
Hello All,

I have an 05 Trailblazer I have owned since 2006 and I had to replace the positive cable earlier this week. I took it on a long drive over good and poor dirt roads and decent paved roads with no problems and went home. About an hour later on a drive to the gas station, the battery light came on and the Voltage Meter on the dashboard dropped to approx. 12 volts which told me I was probably running on the battery only. Took it to O'Reilly Auto yesterday and they told me the Alternator was only putting out 11 volts. I took the alternator out and had them bench test and it was able to put out approx. 14.5 volts so not thinking it is the Alternator.

I went over all the wiring in the vehicle and ground is good at all expected spots, the positive cable from the alternator to the battery end rings good as well. I am concerned that the connector to the alternator from the PCM has a problem and I don't know where I can ring it out from on the PCM end to make sure I didn't break a wire while replacing the positive cable.

Does anyone have the wiring diagrams or suggestions? I saw in search results that there was a resources section at one point but I can't find it anywhere now.

Any help is greatly appreciated.
 

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2005 chevy trailblazer_ls
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11 Posts
Discussion Starter #6
I think the 2004 version would more closely match the 2005. All my other searches turn up the 2004 information and I know there were some differences moving from the 02-05 run and 06 on.
 

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2005 chevy trailblazer_ls
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11 Posts
Discussion Starter #7
now for the next dumb question, on the PCM side, once you have the connecter off, which corner is pin 1?
 

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2005 chevy trailblazer_ls
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11 Posts
Discussion Starter #9
That was a great help from both of you. I isolated down to the grey wire. Now to replace as much of the wire as I can and the connector in the hope that catches the break.
 

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Do this instead of abandoning a full run of factory wire:

Break the circuit in half. Then test both way to see which side has the problem. Try to find a connector that conveniently offers you the opportunity to back probe the circuit when it's live.

(I said 'backprobe' because we do NOT probe into the tiny spring-tensioned and very damageable female ends of those connections! You can create significant numbers of more troubles than you repair if you front-probe!

If the wire run is a significant amount of length, hidden inside the frame or in an umbilical/conduit/race - then you should never want to just abandon or run new wire.

Another problem: if the suspect wire runs under the carpet and you don't wanna take the seats and carpet up - I can understand that desire to do it easily for you.

But that's wrong on many levels.

Soo-o-o-o ----> why not abandon a suspected "bad wire" and bypass it with a new wire?
Because if it truly has gone rogue and burned off it's insulation and is just microns away from invading a wire running alongside it - you are creating a perilous predicament.​

Repair the problem - don't leave the problem to mess with some other poor circuit that may NOT be as capable of handling inconsistent power or big power surges that can fry. cook and generally let all the magic smoke escape from something expensive (the ECM or the BCM - and any other _CM you might run into....... )

-- this treating the wire as suspect for the whole length (and you said "ringing out" which tells me you are at least electrically intelligent) --- is counter-intuitive.

Leave sleeping dogs to lie.

Watch this guy:

If he can do it ---- YOU can do it too.
 

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2005 chevy trailblazer_ls
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Discussion Starter #11
14 years USN, Electrical and Electronics repair. This is a short run from the alternator to the PCM with a fun bunch of cable runs attaching and detaching along the way. Cut in the middle sounds good to me. Test from there and see.
 

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2005 chevy trailblazer_ls
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Discussion Starter #13
The saga continues.....
I know all the wires are good from the PCM to the Alternator and Alternator to Battery. The Red Wire from the PCM is getting about 4.5 volts +/- .1 volts. I am not measuring any voltage on the grey wire so wonder if it really is the PCM.
I hooked up a lead to the output on the alternator and tested voltage without the battery in circuit and it comes back essentially no volts.
I guess the next step would be to break the grey wire for real and leave the red wire still intact and see what happens. Really hesitant to do that though. Just for good measure now that I remember. I had another alternator in the garage so I swapped that in and got the same results.
My wife is wrapped around the axle about the fact that I changed the positive cable and thinks that is the problem but I disagree because the starter and the rest of the car get voltage when the battery is charged.

Any further input is greatly appreciated.
 

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I hope I didn't read between the lines and see that you ran the alternator (engine running) without the load of the battery on the other end? No!

NEVER NEVER NEVER NEVER NEVER (did I say that enough?) Never run the engine without the alternator "seeing" the battery.

Do NOT disconnect the battery - even for a moment - from the battery when the system is running.

The battery, besides providing a voltage-stable reference to the ECM and other associated voltage-sensitive (and highly damageable) systems, is also a giant 6.0uF capacitor that keeps a load on the alternator all the time.

It's designed to be in-circuit all the time the alternator is excited by the digital driver.... that is, when the engine is running.

Please say it ain't so!
 

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The saga continues.....
I know all the wires are good from the PCM to the Alternator and Alternator to Battery. The Red Wire from the PCM is getting about 4.5 volts +/- .1 volts. I am not measuring any voltage on the grey wire so wonder if it really is the PCM.
I hooked up a lead to the output on the alternator and tested voltage without the battery in circuit and it comes back essentially no volts.
I guess the next step would be to break the grey wire for real and leave the red wire still intact and see what happens. Really hesitant to do that though. Just for good measure now that I remember. I had another alternator in the garage so I swapped that in and got the same results.
My wife is wrapped around the axle about the fact that I changed the positive cable and thinks that is the problem but I disagree because the starter and the rest of the car get voltage when the battery is charged.

Any further input is greatly appreciated.
You REALLY need to have a schematic on your desk all the time for this treasure hunt. Make that : a snipe hunt.

You're dealing with a lot of digital signals and commands here and you better NOT push 12VDC into any of those circuits with a Lo-Z meter (analog, usually) or a 12V test probe.

IF you puncture a wire to find a signal or voltage, you must seal that wound! Use some liquid electrical tape. That's what it's for - to seal test holes.

Either 50/50 or 60/40 electrical solder* or use a really good quality heat-shrinkable self-soldering butt connector. They're expensive, but they are what you need to use to keep signal and voltage from deteriorating at that point.
(* NOT the new, safe to suck on Cal/OSHA solder that will fail you and inserts a lot of resistance to the wires)​

You've also got the possibility of changing a load or dropping a parity handshake and then will need to 'tell the ECM that there's a new component in the system' and it takes a bi-directional scanner - and possibly a contracted link to GM for their downloadable programs to make these parts work and play well together.

This becomes professional stuff - stuff I don't do any more, but I DO know it has gotten a lot more serious and almost impossible for a DIYer any more.

Fix the wires correctly - unplug both ends and run an Ohm test on the individual wires that you fix to check integrity and before you re-wrap the wire umbilical, run the engine in actual running mode and make sure that everything is working.

I'm trying to make this as easy as I can - without talking down to you. I do not intend to offend - but please ---> this is NOT your father's Oldsmobile.




.
 

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View attachment 55434

ALL those warped and overheated wires must be repaired too! Not just the ones with actual holes in them. I can count SEVEN damaged wires - not necessarily burnt-through - but heat damaged.

There is not a lot of sheathing on those wires for obvious reasons (weight + less fuel mileage and higher emissions) and they need every Sillimeter of the original thickness to protect them from driving vibrations and neighboring wires going toaster-element on ya.
 

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Hey ... just for kicks and giggles, watch this guy run down a short....

 

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2005 chevy trailblazer_ls
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11 Posts
Discussion Starter #18
55444

I call it success for the moment. Still gotta wrap everything up and then drive it.
debrief to be posted later.
 

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Hello All,

I have an 05 Trailblazer I have owned since 2006 and I had to replace the positive cable earlier this week. I took it on a long drive over good and poor dirt roads and decent paved roads with no problems and went home. About an hour later on a drive to the gas station, the battery light came on and the Voltage Meter on the dashboard dropped to approx. 12 volts which told me I was probably running on the battery only. Took it to O'Reilly Auto yesterday and they told me the Alternator was only putting out 11 volts. I took the alternator out and had them bench test and it was able to put out approx. 14.5 volts so not thinking it is the Alternator.

I went over all the wiring in the vehicle and ground is good at all expected spots, the positive cable from the alternator to the battery end rings good as well. I am concerned that the connector to the alternator from the PCM has a problem and I don't know where I can ring it out from on the PCM end to make sure I didn't break a wire while replacing the positive cable.

Does anyone have the wiring diagrams or suggestions? I saw in search results that there was a resources section at one point but I can't find it anywhere now.

Any help is greatly appreciated.
I know factory gauges get a bad rap, but in my case the voltage indicator was correct and showing below voltage. I replaced the alternator and the problem went away. One thing I'd suggest is that the hoist bar/bracket in front of alternator (which also holds A/C line) be taken out as it just makes life more difficult and no one seriously plans to replace a motor on such an old car. You can just put it aside for whenever the engine needs be taken out.
 
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