c305 connector repair made things worse?
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Author Topic: c305 connector repair made things worse?  (Read 1030 times)
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phaser125
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« on: May 23, 2017, 07:48:48 AM »

While I have a 2006 Buick Rendeavous 3.6l AWD (not an Aztek, but I know they share most of the guts and this connector in particular), I thought this was the most likely place to find someone with experience...

I've been having issues with the AWD Disable light being on (no ABS light or Service Traction, just the AWD disable).  I know it can be the solenoid valve in the rear but found the details about C305.  Well, that connector was completely full of water and corrosion.  It looked like one of the spring metal bits in the female side of the connector with the 3 wires for the AWD had corroded to the point of falling apart.  As a first attempt, I used a nail file to clean up the connectors as well as some electrical connector cleaning spray and did the best i could.  After cleaning the pins on all three connectors (the 8 way plug going to the fuel tank was badly corroded as well), I had a fuel guage stuck on EMPTY and a check engine light related to the fuel tank pressure.  After further messing around trying to clean up the connectors I gave up and removed them, directly soldering each cable.  I carefully made sure, and then re-checked last night, that all the wires from each harness goes to the correct wire inside the cabin.  Still, no gas guage and the check engine light comes back if I clear it.  After disconnecting the battery for a while to reset things and reconnecting, the fuel guage went briefly to the maximum "Full" position, but then suddenly drops back to EMPTY.  I've been trying to check voltages on the leads, but since I'm not 100% sure how it acts when everything is working normally, it's hard to tell.  If I disconnect the fuel guage sense wire (purple), leave it off, then disconnect the battery and reconnect, the fuel guage goes to full as expected, and stays there.  If I touch it briefly to the wire from the sending unit, the guage does not go down (despite the guage working perfectly before I cleaned the connectors), and if I leave it connected, it will stay on full for a minute or so and eventually "drop" to 0 and never go back up even if I disconnect the wire again, almost like something is getting overloaded.

BTW, the AWD Disable light is still on, so I didn't even fix that while apparently making everything else worse... Luckily the fuel pump wires are still keeping the engine running :-P
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phaser125
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« Reply #1 on: May 23, 2017, 07:51:50 AM »

Also this weekend after the "cleaning of the c305", my air conditioning blows nothing but warm air.  I'm beginning to think I'm cursed, as there should be no way these two things are related... Right?
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Bill Salina
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2003 Gold FWD Aztek - aka "The Warthog"


« Reply #2 on: May 27, 2017, 02:47:10 AM »

Phaser125 - Yeah, I don't think that the C305 connector has anything to do with the A/C.

On my 2003 Aztek, I have to watch what happens at startup.  If I start the car and then shift into reverse, I should hear the doors lock.  If that doesn't happen, it means the body control module (BCM) hasn't initialized properly.  There is something in the BCM that appears to have some effect on the AC, because when the BCM doesn't initialize properly (in my Aztek), my AC will blow warm.

To fix it, I shift back into park, turn the key to off, count to 5, and then restart the car.  This always fixes the problem.

The first time this happened to me I drove the car over to my dealer (with no AC on a 95F day here in Atlanta), pulled it into the service area, parked it, and shut it down.  The dealer came back a little while later and said they couldn't find anything wrong and that the AC was working fine. 

Now, the gas gauge - usually the problems on these is that the gauge will indicate full, then suddenly drop to empty.  Sometimes it will work ok for a bit, like until you hit 3/4 of a tank, and then drop to empty.  This is usually caused by either the C305 connector or a bad sending unit (on the fuel pump, in the tank).  If your gauge was working properly and only started acting up when you began messing with the C305, then it has to be the C305 area that's causing the problem.  My guess is that you either hooked up a wire or two wrong when cutting out the C305, or you have a short to ground on one of the sender wires. 

When you soldered the wires, how did you insulate them?  Did you use shrink tubing, electrical tape, or something else?

How did you close the C305 hole when you finished?  If you bolted the cover plate back down, are you sure it's not cutting through any insulation you used and into the wiring? 

I would check all the wiring around where the C305 used to be for shorts to ground.

The C305 usually gets damaged by water inside the car getting down into the connector from inside the car (from wet feet, condensation, an open window, etc).  I got lucky and mine looked brand new inside (no corrosion) and the outer water seals had done a good job of keeping water out from the outside.  SO I sealed the inside cover plate with RTV.  My gas gauge always indicated empty, so for 9 years I drove it that way using my trip odometer to determine when to fill up.  Then last year I replaced the fuel sender and the gauge has worked great again ever since.

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Bill (aka Bird Dog)
2003 Gold FWD Aztek "The Warthog"
phaser125
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« Reply #3 on: May 31, 2017, 07:07:12 AM »

I actually haven't sealed up the hole yet where the cables go through although I did put a bunch of electrical tape on them and even put a split piece of rubber hose on the metal edges and zip tied it all there so it couldn't slide around and wear on the wire casings.  I planned to plug the hole but needed to know if it was working first, which of course its not

I soldered and shrink wrapped all the wires, including some "extensions" about 6" I had to add to be able to work with the wire.  Do you think there's any reason adding a few inches of wire to the cabling could cause the sensors to fail like that?  With the wires the way they were, working on them without extending them at all was difficult, so I soldered and shrink wrapped both ends of a short extension piece to all the wires on the 8 conductor connector when I removed it.  The other two (one for the ABS sensors wires and one with the AWD wires) I managed to solder direct without extending.

Interestingly, it seems GM had at least TRIED to prevent the c305 corrosion issues by the time they got to the 2006 Rendezvous, as the connector was "sealed" with black rubber that was poured / melted / molded into the plugs from the top side from the factory, which was actually a bit of a pain to remove to make sure I had all the right wires and pins in the right places.
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Bill Salina
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« Reply #4 on: May 31, 2017, 09:15:49 AM »

You are making me wish I still had my factory service manuals with the wiring diagrams...

Since the fuel pump is still working, that circuit must still be ok.

Right now I'm thinking maybe a ground is not connected properly, or is missing?

It's easy to second guess yourself ("maybe I shouldn't have messed with C305") but the thing is, if you'd have done nothing eventually you'd have ended up stuck on the side of the road somewhere when the fuel pump pins corroded out.

I wouldn't think that adding 6" extensions inline would cause a problem with the non-ABS sensor circuits.  Sounds like you did everything right (solder and shrink wrap).  

 If you still have the C305 block and all the things that plugged into it, I would check that what goes in on one side actually connects to the thing on the other side.  I wouldn't put it past GM to have a wire here or there that doesn't connect up with the matching color wire on the other side.  

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Bill (aka Bird Dog)
2003 Gold FWD Aztek "The Warthog"
phaser125
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« Reply #5 on: May 31, 2017, 09:30:37 AM »

Thanks for checking in again.  I did have a wiring diagram I found on another forum post about doing a "c-205-ectomy" and was following the diagrams pin for pin.  Actually thats why I picked all the rubber gasket material out of the top side connector as I was going, so that I could ensure the wire colors etc. matched up with what the diagrams were telling me.  Unfortunately, I'm nearly 100% confident that I have the correct wires going to the correct places :-P  I wish it were that simple.  Since I cannot see where the wires go after they disappear above the fuel tank, I have to wonder if maybe somehow one of them is no longer attached correctly on the other end where I can't see.

One thing that I regretfully did not do, was disconnect the battery when I cleaned the terminals the first time around.  Is there any chance that I could have shorted something, even with the key off and out, that could have messed up the computer?  I'm not sure where those sensors connect, is it to the ECM or the BCM?  Hopefully I didn't fry the inputs on that.
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Bill Salina
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« Reply #6 on: June 01, 2017, 10:05:54 PM »

I think as long as you didn't turn the key on, you should have been ok.  I don't think power is applied to those circuits unless the key is in the run or start positions.  But I could be wrong...  my manuals would have told me... (sold them on ebay a few months ago)...

When my gas gauge went bonky on me about 9 years ago I suspected it might be the C305 connector.  SO I drilled out the rivets, pulled the cover off, and all looked fine.  I replaced the rivets with bolts (and Nynuts) and figured it was the fuel sender in the tank.  I finally got around to changing that last summer (for 9 years I used my trip odometer to determine when to fill up).  It really wasn't all that hard.  Hardest part was getting the tank back up into place (it kept trying to fall off my jack). 

It's possible that the connector came off where the harness plugs into the top of the tank.  I might still have some photos left from when it did the job, but I'm pretty sure you can't even touch those connectors (let alone see them) with the tank up in place. 

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Bill (aka Bird Dog)
2003 Gold FWD Aztek "The Warthog"
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