Problem with a keyless any ideas???

[Ranger SVO]

Two years ago I put a keyless entry in an 02 Trailblazer. According to the customer it worked flawlessly until today. Heres is what I've done so far.
1. Replaced the data interface with a new one. still didn't work
2. Replaced the data interface again, still don't work.

Obviously the approach above is not working.

3. Hooked up my OTC Scan Tool to the diagnostic connector and reinstalled the first data interface. Pushed lock on the keyless. Saw the data stream on the OTC screen.

4. I know data is being transmitted to the vehicle BCM. Check the BCM output and saw NO lock command being sent to the driver or passenger door modules.

Where do I go from here, while I can see a data stream being sent to the BCM, I have no idea what its saying to the BCM. But I also know that there is no way I can have 3 faulty data interfaces. I have installed around 90 of these interfaces and have only seen this one problem.

How do I prove the vehicle is at fault.

[OnYrMrk]

cause the install is 2 years old. No telling how or what was done to that car since.

[JeremyC]

Bypass the Vehical BCM.

Ok picture a fault tree.

At the top is data interface

next would be the wiring from it to the BCM

Next is the BCM

and the last thing is the wiring from it to the lock.

Your on the third interface, and haven't fixed the problem.

first step of tree c/w

next is the wiring.

You said that you know the siginal is getting to the BCM, so your wiring should be good.

second step in the tree c/w

Next is the BCM (factory part I am guessing)

Yor not getting a signal out from it.

third step c/w, ops check bad

The last step isn't really needed, but it does help you verify.

Find a way to bypass the BCM and send an unlock pulse to the door.

If it works you know its not the wires. so your back to step 3, and the bad BCM.

C/W = complied with
OPS check = Operational System Check

[Ranger SVO]

I like people who think logically.

The problem I am having with proving the BCM (Body Control Module) is bad is the fact that it is communicating with my scan tool and if I push the lock button on the door(not the keyless), I see a lock command being sent to the other doors.

So the BCM is either ignoring the command from the data interface or it does not know what to do with it.

Keyless cannot be done conventionally in this vehicle. The passenger and driver door have there own seperate control modules. The rear doors and tailgate is controlled by Liftgate module.

I like a challenge but this one is going to get old really fast.

Since 02, I have done alot of keylesses in these SUV's and this is the only problem I have run into. Also I have a mild case of Excessive Compulsive Disorder, so I can assure you that each and every install is exactly the same in every Trailblazer. All the way down to the number of tie raps use in each install (3).

[JeremyC]

I know the feeling. We have 23 F16s that I work on every day. They are all the exact same, but each one has its own set of problems. Thats why the fault tree came to mind. I use them every day.

Well if the BCM is ignoring the command, change the way the command is sent. You said the door lock buttons work, would it be possiable to use them as an interface?

Without knowing the system its hard for me to help. But there has to be a way to trick the BCM into responding.

If not, see if the dealer will loan you a BCM for trouble shooting. Tell him you think the software or hardware has a internal glitch and see if they will let you temp install one.

Its very possiable one part of the BCM broke causing the problem. I see it all the time. An internal computer will drop one function (like symboligy for a display) but everything else this computer does still works perfectly.

[Ranger SVO]

I won't see the Trailblazer again til Wendnsday. But I could try what you suggested. Using the OTC, I can tell the car it has a factory keyless, then program the data interface to send the same command to the BCM that the factory keyless would. And see what happens.
(I miss the good old days when all I needed was a keyless module and 2 relays)

A freindly car dealer in Abilene Tx aint happening. These dealers would lie and steal from their mothers to make a sale. These people are so two-faced it aint even funny.

Anyway I am convinced its the BCM, but I will need to convince the customer.