4wd System Operation & Help Thread

I actually found the scan tools bridging the DLC grounds by accident while chasing an instrument cluster problem on a Chevy pickup, I found it odd that it worked fine with a scan tool connected but went nuts when it was disconnected.

GM trucks are known for instrument cluster failure but I pulled the cluster out to check powers and grounds to be sure and determined it was missing a ground, reserching ground distribution I discovered the Pin 5 of the DLC shared the same ground as the cluster.

After that I did some testing and sure enough with the scan tool connected the ground was good so that confirms the scan tool has to be bridging the 2 ground pins of the DLC.

 

Is this picture telling me that all these systems are using EE and EH for a ground? I know where EE is, where is EH? Could the bad ground be any of the wires coming off the gray box? Or just at EE or EH? Yes, the 4WD light came back on right when he unplugged the scan tool.

 

How would I test this ground? Ideally I would put one probe of the multimeter on that ground and the other one on the negative battery terminal. The multimeter would be set to amps and I would look for 2.5ish amps= good test. Right?

 

Ahh, EH is for the 4 cylinder. I’m catching up. This is definitely above my skill set.

 

it's designated EE is on the 4.0L engine and EH on the 2.7L engine.
Yes that is everything that is on that ground, since we know it works with a scanner plugged in the problem has to be between the ground point and the junction box where it is all connected or the junction box itself.

Ground point EE is on the back of the passenger cylinder head.
To test a ground with a meter you want it set to volts DC.
One end connected to battery negative and the other connected to the ground your checking, key on so the ground is loaded you should see no more than 0.2v




This is the Junction Box referenced in the diagram, it the beige box is under the passenger dash next to the PCM

 

EE =4.4 amps between EE and battery negative


ED = 4.0 amps between ED and negative battery terminal. Yes, my daughter does not want be helping me.


Are these good test?

 

That's ohms not amps and no you should see basically 0 ohms using that test so if your tester connection was good I'd say you found your bad ground.

 

ED= 0.00 volts key on
EE= 0.00 volts key on

 

Did you give all the wires going to that ground a tug to make sure none are broken?

 

You need to move the black test lead to the COM on the DMM to properly measure volts or resistance.

The way you have it hooked up is only for measuring currents up to 10ADC with the dial in that one 10A position. Im surprised it gave any reading the way its hooked up and the way the dial is set

 

Oh good catch, I totally missed that

 

Now that I have the DMM hooked up right I’m getting .1 or .2 ohms and 0 volts with key on.

 

And 1.5 ohms on all 4 wires coming off EE and 1.5 ohms at ED with the key off. I’m ready blow this thing up. I might be easier to just drive around with scan tool plugged in.

 

I understand electrical diag is frustrating for many people but I have faith we can find it.
I think my next step if you are sure the wires are all good at the back of the cylinder head is to unplug the connectors at the No2 junction box under the dash and look for corrosion and/or burnt pins.

This is where it is behind the glove box.

 

I sure do appreciate all your help and time. I have to work the next two days. When I get home I will see if I can have one my mechanics test EE for me just to make sure I’m doing it right. Then I’ll get back after it Friday. Thanks again.

 

I mean we know what circuit the problem is on, it's just a matter of finding the broken wire or corroded connection.

 

Everything inside the tan box is pristine. A new charcoal canister did not fix the problem. I just had to try it, I know. I went to autozone and plugged in their obd 2 scan tool and 4WD worked. I unplugged it and it immediately started flashing again. On the drive back from deer camp last night I noticed my cruise control isn’t working either. I assume it’s related. Fun times!

 

One way around that is to just jumper the two grounds together at the OBD port. It won’t permanent fix it but good enough to get it working in time for an FJ case. Or buy an ultra gauge and leave it plugged in.

 

So we know 100% we have a bad ground, I think the next step is to backprobe connector PA Pin 18 of the junction box and check voltage. That will narrow it down alot.

 

That may be a temporary "fix" but I wouldn't recommend doing that because if the main ground at EE is indeed missing then everything on that circuit will try to ground through the much smaller gauge wire at the OBD port and could start melting things.