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Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 27814
Experience:  14 years GM dealer Technician.
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My rear door locks intermittently unlock and or lock at

Customer Question

hi, my rear door locks intermittently unlock and or lock at times and not at times, with the key fob OR the driver/passenger switch on the front doors.
JA: Have you checked the fob's battery?
Customer: I have not, considering that the locks will not lock/unlock with the front door switches either
JA: What is the model/year of your Chevy?
Customer: 08 chevy duramax
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: I would prefer to fix it myself. This is my first attempt to search for solutions. I did however use my test light and checked the fuses that are inside the driver side panel of the dash. Every fuse (except for two 2amp fuses) and except for all of the lock and unlock fuses made the testlight light up. BUT when I took the lock and unlock fuses to check them visually, they appear to still be intact
JA: Anything else you want the mechanic to know before I connect you?
Customer: not that I can think of
Submitted: 8 months ago.
Category: Chevy
Expert:  Pete replied 8 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Is this issue only occuring with one rear door and which door is it on your model here?

Is it acting up both with locking and unlocking with the remote and the interior lock and unlock buttons?

Let me know so we can continue,thanks Pete.

Customer: replied 8 months ago.
Very sorry for my delay as well. I have a sweet Grandbaby who is fighting sleep. :)So let me try to answer your questions.First, let me add that my interior passenger window switch has not functioned in a couple of years.For the last 1-2 weeks, (as far as I know) it was only my rear driver side door that would not unlock (at times)..and then at times it would.Now today is the first time that I noticed the rear passenger side not unlocking.It's possible that I noticed it because it's the first time that I needed to put my Grandbaby in the back passenger side since it started acting up 1-2 weeks ago.So today, neither back door will lock or unlock with either the fob or the door switc.
Expert:  Pete replied 8 months ago.

When you try to lock or unlock them if you grasp the lock knob at the top of the door do you feel any movement at all?

Customer: replied 8 months ago.
I can physically unlock and lock them.I do not feel any "extra" movement coming from down inside the door, nor do I feel any resistance.
Expert:  Pete replied 8 months ago.

Do you hear any clicking noises inside the door at all when trying to operate them?

Customer: replied 8 months ago.
Expert:  Pete replied 8 months ago.

O.k.,first step.In your instrument panel fuse block locate the UNLCK 1 and LCK 1 (15 amp) fuses and make sure they are both o.k.If these are o.k. if you have a test light or multi meter test for power on these fuses when locking and unlocking the doors electronically.If you have no power across these fuses what fails is the Lock/Unlock PCB relay in most all cases.This unfortunately is a relay that is integrated into this fuse panel itself and cannot be replaced separately as it has to be replaced as a complete assembly with the instrument panel fuse block.The door locks can start to fail one at a time like this here as this relay controls these circuits individually.It is more of a control module/relay since it has so many different functions built into it.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete