2003 Chevy Avalanche Back Door Unlocking problem

[2003truckman]

I have a 2003 Chevy Avalanche with power locks. The truck used to lock the front and rear doors when the truck was taken out of PARK. And unlock both the front and rear door locks when the truck was put back in PARK.
Now the truck will lock the front and rear doors when the truck is taken out of PARK but will only unlock the FRONT driver and passenger door lock when it is put back into PARK but will NOT unlock the back sit door locks. It will lock the back doors even if you manually had unlocked the back doors but will NEVER automaticly unlock them
The front power locks will lock and unlock with the remote but the back locks will LOCK but NOT unlock with the remote.
The drivers handle lock and unlock the front driver and passenger doors but the it will ONLY lock the back locks.
And time you want to have the back doors unlocked you have to manually unlock the doors.
Does anyone have a suggestion what is wrong and causing this problem?
thanks

[bradrhale]

what changed?? on alot of chevy models, you have 4 different selections where it comes to unlocking/locking doors. you can have it set to unlock when put in park and lock when taken out. combine those to get the 4 differenet ways. i forget how to but know it can be done.

[crabtruck]

Welcome to the forum 2003truckman.

Try switching your Rear Door Lock relay with Rear Door Unlock relay
in left IP fuse block.
May just have bad relay.

[2003truckman]

I do not have a separate Rear Door Lock relay. I have a LOCK RELAY (153328867) and an UNLOCK RELAY (15328867). And if this was bad wouldnt the front door not unlock?
Any other suggestion

[BernieB]

Check the position of the child safety interlock. Should be a sticker about it on the doorframe.

[crabtruck]

Originally Posted by 2003truckman

I do not have a separate Rear Door Lock relay.
I have a LOCK RELAY (153328867) and an UNLOCK RELAY (15328867).
And if this was bad wouldnt the front door not unlock?
Any other suggestion

I'm going to suggest you don't throw this one away just yet:

Originally Posted by crabtruck

Try switching your Rear Door Lock relay with Rear Door Unlock relay
in left IP fuse block.

Here's why:
1) It's free.
2) In the time it took to note those numbers you could have tried it.
3) You don't have relays for all locks, just rears.
....Your front locks are supplied through left and right circuit breakers.

Of course I could be totally wrong,
but it might be worth a minute of your time.
I don't mind if you disagree, but it sounds like I wasted my effort.

[2003truckman]

Crabtruck, I did not mean to offend you. I did trying switching the relays and this did not correct the problem. I forgot to meantion this when I asked for anyother suggests. Accept my apologies.

I do appreciated the free advise.

I still need to check the child safety advise. I am looking in my manual where this would be.

any other suggestions will be appreciated.

[BernieB]

Originally Posted by 2003truckman

Crabtruck, I did not mean to offend you. I did trying switching the relays and this did not correct the problem. I forgot to meantion this when I asked for anyother suggests. Accept my apologies.

I do appreciated the free advise.

I still need to check the child safety advise. I am looking in my manual where this would be.

any other suggestions will be appreciated.

If you have child safety locks on the rear doors, and most vehicles after about 1995 did, then there should be a sticker either on the glass, or on the door frame itself. The purpose of the interlock was to prevent kids in the back seat from opening the doors when it wasn't safe. It disables the electric unlock and the door handle, so the door can only be opened from outside with the handle or the key.

[crabtruck]

My bad, I didn't get that you tried the swap.
Hardest part of web info is not being able to SEE
what you're talking about.

First check Bernie's child lock idea,
and if that doesn't get it,
let's deal with I made a mistake.

Those relays are NOT lock and unlock seperate controls.
They are labeled as such, but BOTH are required for each act.
Having done the relay swap actually helps narrow the problem.
Proves all wires from relays to door locks are good.

Next is see if unlock relay is getting command to open.
Put your fingers on relays and see which one clicks when locking.
Should feel no click when unlocking (because of failure).
Relay that does not click should be pulled. (No key ever needed)
Check for 12v to ground on socket #86. (control hot)
Check for 12v to ground on socket #87. (unlock hot)
These share same fuse, you are checking connections.
Next test only happens for a moment. (Same amount of time as click felt)
Check voltage to ground on socket #85 - will jump to zero from random.
To see what to expect you can compare what happens at other relay.
This is check to see if relay getting signal to unlock - probably doesn't.
If you were to use a fused jumper from #30 to #87 (with lock relay in)
doors should unlock. Just FYI - no need to do.

Relays are controled on their #85's with a "ground" signal from BCM-body control mod.
To see if BCM sending signal you can check for voltage changing to zero at
connections A3(Tan/Blk)unlock and A6 (Gry/Blk)lock.
If no ground being "sent" then BCM is source of problem.

Source but not proof it's bad, may have wrong instructions from "you"
Check owners manual for a setting that deliberately disables the rear unlock feature.
If BCM is bad it should have thrown a code (even if no light currently on)
So really look for "feature" or Bernie's child lock.
Double check for stored codes.

[hotrodpc]

I do not believe this has anything to do with your relays at all. It has to do with your power door lock programming. You can even program those locks to NOT lock in park if you don't want them too, you can also program them NOT to lock until I think its 8 mph instead of instantly when you come out of park into drive or reverse. You have programmable locks. Check out your owners manual how to change it. I think it can also be done thru the DIC (Driver Info Center). However, I do charge for advice, so if that fixes your issues, get my PayPal email addy from me in PM to send payment.