4wd System Operation & Help Thread

Backprobe the White/Black wire (Pin4) at the actuators with them plugged in and the key on and see what you get, I'm suspecting to see 12v there since all your limit switch signals are stuck at 12v which would indicate an open ground to the actuators.

 

Sure makes sense with everything stuck at 12v

 

The TC actuator switches both read 0 on the blk/wht wires. The ADD up front reads 12 volts on the blk/wht wire and pin 4 reads .02. I also plugged in the new ADD to see what would happen and got no change. Would I need to unplug the battery and the 4WD ecu and then plug in the new ADD, then plug back in the 4WD ecu, then hook up the battery? In ordered to get everything to reset.

 

I said Black/White, I meant White/Black (brain fart)

So you have 0v on the ground (White/Black) of the actuators with them plugged in but all your limit switch readings at the ECU are 12V?

 

I made a mistake, pin 4 at the tc actuator in 0, pin 4 at the ADD reads 12.

 

Ok so if that's correct your missing the ground at the ADD, you can supply it with a bypass ground temporarily and see if things work properly.

 

How would I do that? It should read 0, correct?

 

Yes the White/Black wire (Pin4) at both actuators should be ground (0v), you can run a wire from a know good ground to your backprobe at pin 4 if the actuator and see if things work with it connected.

 

Thank you, I’ll give that a try tomorrow. I’m definitely not pulling ADD till I know more.

 

The dealership is telling me that my check engine light is causing my 4WD not to work. I have a check engine light on because my charcoal canister is bad. Just needs replaced. The tech said when he cleared the code the 4WD worked fine. Hmmmmm, I don’t know if I buy that. Anyone think it sounds a little fishy?

 

No a CEL will not affect the 4wd system, it does share some grounds with other things that could cause a CEL though.

 

That’s what I thought. They said when they cleared the codes the 4WD works fine. We’ll see tomorrow when I pick it up.

 

Weird, the 4wd is in no way connected to the engine management system other than sharing a couple grounds and the vehicle speed signal.

 

fishy at best. He obviously doesn’t understand how the 2nd gen system functions

 

Isn’t that the truth.
A scan tool and the 4WD system have nothing to do with each other on a 2nd gen.

If it were a 3rd, maybe. Since they actually incorporated fault codes for the 4WD System.

 

Welp, I when to get my truck this morning and low and behold the 4WD light was still flashing. Pretty heated, I went back in to tell the service rep my 4WD was not working even though he said it was when I called this morning to double check. He went and got a scan tool from the shop and brought it to the truck. After hooking it up and clearing all the codes the truck went in to 4WD just as it should. As soon as he unplugged to tool and the ecu started throwing codes and the flashing started again. I watched the whole thing happen. The codes are in this the picture below.

Basically all the codes for the vapor canister replacement. I have one on the way. They wanted a grand to do it and politely said no thank you. I’ll report back when I get it installed. Can I clear the ecu by disconnecting the battery or do I need a scan tool to “really” clear the ecu? Hope this helps someone in the future.

 

Ah I know exactly what's going on now, with most scan tools connected pins 4 (Chassis Ground) and 5 (Sensor Ground) of the DLC are shorted together which will temporarily "fix" a bad sensor ground while a scan tool is connected.
Remember we were chasing a bad ground last time you posted, I'd be willing to bet finding the problem and fixing that ground will fix your EVAP code(s) too as that is on the same ground tree.

 

You say “ As soon as he unplugged the tool, it started throwing codes.”

Is this literally as in “just as the scan tool was unplugged”?

Or shortly after the scan tool was unplugged?

I’ve never heard of an Evap code to cause the 4wd to not engage.

I think there may be more to the problem.

 

That pic is too small to read. Did you ever find the ground issue we were cashing a few weeks back? I bet thats your issue.

 

Dang @Dm93 beat me to it, with a better explanation too