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Discussion Starter #1
Tow haul light and no overdrive light comes on and off the abs light is either a LF Speed sensor or a speed sensor on the t-case. As u can see if very annoying to drive. Thankfully I live a lot closer to work than the normal person. Both wires are cut for the tow haul at the shifter so I don’t see how it’s getting told to be put into tow haul mode. I just bought this truck 3 hours away and of course it didn’t do any of this until I get home. Just really hope I can figure this out. I’m hoping the overdrive light is something to do with the speed sensor being faulty and I’m pretty lost about the tow haul. Here’s a video I took a little while ago on my way to work.




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I'm afraid you are in for some exploring. The tow/haul switch is a momentary contact switch. It connects a light blue wire from the BCM to ground. That means that anything that momentarily connects the light blue wire between the switch and the BCM to ground will act just like the switch itself. The transmission will toggle between tow and not tow.

You apparently have an intermittent grounding condition on that wire. You need to find where it is rubbed through and fix it.

Alternatively you could cut the wire at the BCM. The one you want is in connector C3 in socket B11. B11 is second from the end between two empty sockets. C3 is brown.

The BCM is mounted directly under the steering column. It has 4 connectors. Three are on the end and one is underneath. I think C3 is the right one on the end but I'm not sure.
 

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Discussion Starter #3
I'm afraid you are in for some exploring. The tow/haul switch is a momentary contact switch. It connects a light blue wire from the BCM to ground. That means that anything that momentarily connects the light blue wire between the switch and the BCM to ground will act just like the switch itself. The transmission will toggle between tow and not tow.



You apparently have an intermittent grounding condition on that wire. You need to find where it is rubbed through and fix it.



Alternatively you could cut the wire at the BCM. The one you want is in connector C3 in socket B11. B11 is second from the end between two empty sockets. C3 is brown.



The BCM is mounted directly under the steering column. It has 4 connectors. Three are on the end and one is underneath. I think C3 is the right one on the end but I'm not sure.


Ok I will check that out thanks for the info. It’s def acting like a loose or broken wire I just was just confused how with the wires to the button being cut. Thanks for clearing that up. Do u think the no overdrive light is related?


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Discussion Starter #4
Got In my truck and closed the door and just the no overdrive light came on. So I kept opening and closing the door and it would come on and off as I did it...




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Discussion Starter #5
Ok so I found the light blue wire coming from the connector for the button on the shifter. The ground wire is spliced into this peach colored wired that doesn’t look like something gm would do but correct me if I’m wrong??

IMG_0882.jpg




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Discussion Starter #7
So for some reason who ever I bought this truck from had to put the horn on a button which is wired to the black/yellow and they had it grounded to one of the bolts mounting the lower metal shield on the column (which i accidentally ran over backing out of the garage ) and since I un grounded the horn both the tow haul and no overdrive light did NOT came on while I drove it about a mile. Idk how that would have anything to do with it but that’s the only thing I took off. The black/yellow wire is mounted right above the light blue wire for the tow haul into the module. IMG_0885.jpg


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No that doesn't look quite factory but it looks better than most non-factory work. I haven't been able to find that wire so I don't know what it is supposed to be.

In the video I think it is making momentary contact every time you close the door so that it toggles between states. If you get the wiring right I think it will all be sorted out.

The black and white ground wire is supposed to go to a junction block in the IP relay block, then to a splice and finally to ground G203. However, the only wires I can find in that circuit are either black and white or solid black. I don't see any tan or peach colored wires.

I'd be tempted to cut the black and white wire out of the splice you show and give it a separate grounding point. Then see what happens.

I don't think there is a problem with G203 because there are 37 things that ground through it and if it had a problem you'd have more troubles than the tow/haul switch.

It looks to me like there are 3 tan wires coming together at the splice as well as the black and white one.
 

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Discussion Starter #9
No that doesn't look quite factory but it looks better than most non-factory work. I haven't been able to find that wire so I don't know what it is supposed to be.



In the video I think it is making momentary contact every time you close the door so that it toggles between states. If you get the wiring right I think it will all be sorted out.



The black and white ground wire is supposed to go to a junction block in the IP relay block, then to a splice and finally to ground G203. However, the only wires I can find in that circuit are either black and white or solid black. I don't see any tan or peach colored wires.



I'd be tempted to cut the black and white wire out of the splice you show and give it a separate grounding point. Then see what happens.



I don't think there is a problem with G203 because there are 37 things that ground through it and if it had a problem you'd have more troubles than the tow/haul switch.



It looks to me like there are 3 tan wires coming together at the splice as well as the black and white one.


That black and white wire goes to a aftermarket button for the horn I just cut that wire at the butt connector and removed the whole button for now. I’m going to replace the steering soon and figure out why they did that with the horn. I didn’t try to follow the peach wire very far but I think IIRC It was going towards the clock spring area. I’ll have to double check that. Is there a good link for a schematic ur referring to for the wiring diagram under the dash?


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Discussion Starter #10 (Edited)
Nvm black and white wire is going to tow haul connector not horn. Sorry about that I had them mixed up until I looked at the picture again

Where would u suggest I ground out the black and white wire once I get another shifter?


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The connector you pictured is C201 on the steering column. It is a main connection between everything in the steering column and the rest of the truck. It includes the wiring for the horn, turn signals, air bag, ignition switch and everything else on the column.

There is a device that looks like a large tape measure in the column. It is actually a coiled up strip of plastic with multiple wiring traces in it like a printed circuit. It is called the clock spring. As you turn the wheel the clock spring winds up and unwinds but keeps constant contact.

All of this flexing eventually leads to it breaking. It carries the power for the horn button, any steering wheel switches and most importantly the power for the air bag. If that is going bad you will lose various parts from the steering wheel. I suspect it is on the way out and the first thing to go was the horn so the PO installed a separate switch. If I'm right you will soon lose the air bag and steering wheel switches.

I didn't mention C201 before because it should not have any potential for intermittent contact like you are seeing. What it would do if it was bad is just not make any connection at all for the tow/haul switch and it would stop working.
 

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Discussion Starter #12
So if ur right I would need a new clock spring?


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Discussion Starter #14
That’s ok I’ll worry about that later if I even hook it back up. Just glad I can drive the truck other than my 5 mins drive to work.


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Does that mean that the tow/haul situation is resolved?

What did it?

If disabling the wire from the C201 connector did it then the problem is most likely in the steering column wiring. Much of that is part of the turn signal switch so that replacing the switch replaces most of the wiring including the horn wires but not the tow/haul wires. The clock spring may be okay and the combination switch wiring may be the problem. More testing is needed.

Where was the tow/haul wiring cut before? If it was near the switch, in the column then that would still leave the wires running the length of the column as suspects.
 

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Discussion Starter #16
All I did was remove the wiring to the button for the horn which I’m assuming was causing an unwanted ground. As soon I did that no more problems. The tow haul wiring had the light blue wire going to the module and the ground going into the peach wire. I’m not sure where the ground for the button on the shifter (black/white) is suppose to go.


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It could be that the horn button was wired in wrongly and was using the tow/haul circuit for a ground. Then if the spring on the button was weak or if there was something floating around inside it there could have been momentary contact that wasn't long enough to activate the horn relay but was enough to trip the electronic circuit for the tow/haul.

The black and white for the tow haul should go to a better ground than it has. When you get around to fixing it you should look into running a wire to G203. It is on the left end of the dash above the fuse panel and near the instrument cluster opening. Perhaps the best way to get to it would be through the instrument cluster opening or by removing the fuse panel. There is a similar ground G200 on the right end of the dash.

If you can't get to G203 then I would try to find the connection on the back of the relay panel that it originally went to and do something with that. Perhaps a scotch lock onto another black and white wire would do the trick since they should all be grounds of some sort. This circuit only carries trivial amounts of current so it wouldn't overload any other ground but the ground has to be good.
 
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