2003 Escalate EXT Rear locks

[tirwin88]

I have a 2003 EXT that we just purchased. When I hit the lock button on both the remote or the front panel, the locks in the front work, but the 2 back locks do not. Any idea where to check first? We have to manually reach in and hit the locks.

[Tech II]

Question......so you hit the lock button, the fronts lock, but the rears don't.......you manually lock the rears.....if you hit the unlock button, do just the fronts unlock, or do the rears unlock also?

Or if everything is locked, and you come to a stop and put in Park, do all doors automatically unlock?

[tirwin88]

If I hit the lock button on the front driver side, only the front lock or unlock. The rear locks do not work at all. I have to manually lock them by reaching in through the front seat to the back.

If I use my remote, the front will lock and unlock, but the rears do not.

[Tech II]

You did not answer my questions....

[tirwin88]

Originally Posted by Tech II

Question......so you hit the lock button, the fronts lock, but the rears don't.......you manually lock the rears.....if you hit the unlock button, do just the fronts unlock, or do the rears unlock also?

Or if everything is locked, and you come to a stop and put in Park, do all doors automatically unlock?

Sorry thought I did.

To your first question just the Fronts unlock

To the second question when in Park, nothing unlocks.

[Tech II]

If you have all the doors locked, and you hit either unlock button on the passenger or driver's door, and only the fronts unlock, then it could be a number of things.....

Since you just bought the vehicle, you do not know the history of it....for example, you don't know if one rear door stopped working first, or if they both stopped working at the same time......

This is how the rear door locks work....the driver's door lock switch sends a signal to the Driver's Door Module....the DDM unlocks/locks the driver's door....the DDM also sends a signal via Class II serial data, to the Body Control Module, or BCM....

The BCM sends a signal(class II) to the Passenger Door Module, PDM, and the PDM unlocks/locks the front passenger door.....The BCM also grounds either the rear door lock relay, or the rear door unlock relay(depending on which action is requested), and this provides power and ground to both rear door actuators.......

So here are the potential problems: a blown or missing, LOCKS fuse(20 amp) in the left I/P fuse block(easiest fix).....a bad lock or unlock relay.....both actuators are bad...wiring problem....or bad BCM......

Hopefully it's just the fuse....but if blown, it blew for a reason....

If not the fuse, you need schematics to diagnose both relay circuits......

[tirwin88]

I checked the fuse and it was indeed blown. I replaced the fuse and it blew again. Seems something is causing it to blow

Any idea where to look?

[Tech II]

OK, this is important....

Does it blow as soon as you insert it, or does it blow when you press lock, OR when you press unlock?

[tirwin88]

Just put a new fuse in. It was fine when I put it in. Then when I hit the lock/unlock button on my remote I saw a spark at the fuse and and it blew.

[Tech II]

This is important.....

Put a new fuse in.....with your remote, hit unlock only....does fuse blow?

Put new fuse in if necessary....with remote, hit lock only....does fuse blow?

If it blows only with one direction and not the other, my guess would be a shorted relay.....

If it blows in BOTH directions, then we have a short that could be anywhere in the wiring after the relays, and it also could be a shorted door actuator, or liftgate actuator(or cargo door actuator, if you have cargo doors)........... a wire coming out of the fuse block could also be pinched somewhere...

You have three parallel circuits, the two door lock actuators and liftgate/cargo actuator.....so If it is a short, it will be an involved diagnosis.....

Your only hope, is finding something with a visual inspection....which is the first thing you should do anyways......the places I would concentrate on, are the fuse block, and the wire looms that go from the pillar to the doors and the liftgate......over time, the opening and closing of the doors and liftgate, cause those wires to flex a lot, and one could have shorted against a sharp edge somewhere.......

But like I said, if a visual doesn't find the problem, you have to be good at isolating circuits to find that short because they are in parallel.....

Hopefully it was a relay, because shorts can be labor intensive....

[tirwin88]

Bingo! Its only doing it with the Lock function. The unlock function was fine.

How difficult is it to replace this part? I am by no means a car person but rely on youtube to help me out. My husband isn't so savvy either.

[Tech II]

That's great.......it's basically plug and play....those two relays are located in the same fuse block as the fuse.......to verify it's the relay, just swap the lock and unlock relays......previously the fuse blew when you hit the lock function...after swapping, it should now happen using the unlock function...if it does this verifies it's the relay....

[tirwin88]

Thanks! Running out today to get more fuses. I blew through them all testing and borrowed from another.

Would it be beneficial to just replace both relays?

[tirwin88]

I just replaced the relay on both and the fuse still blew when I hit the lock button.

[shorod]

You can use a test light in place of the fuse to keep from blowing a bunch of fuses while you troubleshoot. The test light will glow brightly when a short is present versus a fuse blowing. When you make a change and the light stops glowing brightly, the short is no longer present.

-Rod