Pwr door locks out - 99 Silverado

[Tom Naff]

The power door locks on my 99 Silverado have gone out. They will work occasionally, but... mostly not. I have no idea what causes them to change. The fuse is good and I have removed and reset the thing I believe to be a relay (located under the hood)...I even tried reversing the thing...to no effect. Any ideas?
Where can one buy a new relay...if, in fact, that's what the thing is. I sure would appreciate some help.
Thanks....Tom

[crabtruck]

Welcome to the forum Tom.
You didn't mention which level of locks you have, base or up w/ remote.
Base uses two relays, up level uses three relays, both use the Body Control Mod.
Each of your lock motors has a circuit breaker attached.
You also didn't say if the problem is just one door switch or both.
Or if only Lock or unlock works / fails.

First suggestion would be to check connectors are tight and grounds are good.
You should be able to feel the relays engage with your fingertips.
For both types, using either "Lock" switch should trip the "DoorLock" relay.
The "UnLock" switch will not and uses BCM to trip different relay.
Both (or all 3) relays are located in the "Left Bussed Electrical Center"
Any parts store should carry replacement relays, if they are needed.

[Tom Naff]

Originally Posted by crabtruck

Welcome to the forum Tom.
You didn't mention which level of locks you have, base or up w/ remote.
Base uses two relays, up level uses three relays, both use the Body Control Mod.
Each of your lock motors has a circuit breaker attached.
You also didn't say if the problem is just one door switch or both.
Or if only Lock or unlock works / fails.

First suggestion would be to check connectors are tight and grounds are good.
You should be able to feel the relays engage with your fingertips.
For both types, using either "Lock" switch should trip the "DoorLock" relay.
The "UnLock" switch will not and uses BCM to trip different relay.
Both (or all 3) relays are located in the "Left Bussed Electrical Center"
Any parts store should carry replacement relays, if they are needed.

Thanks "crabtruck" for the info. The trouble concerned both door locks and both functions (lock/unlock)..the system has the remote fobs. I think I discovered the problem this afternoon. I checked the fuse one more time and found it still good...however, when I replaced it in the fusebox, the locks began to work. I now believe it was just a loose connection in the box itself or just poor contact with the fuse.