Take the liftgate inside panel off an check the wiring , connections etc....
rear door hatch lock repair GMC Chevrolet
chevy tahoe lift gate not opening
The liftgate will lock any time the vehicle is shifted out of park on vehicles equipped with an automatic transmission and at vehicle speeds exceeding 5 kph with manual transmission. This happens in conjunction with auto door locks if enabled or independently of auto door locks if the feature is disabled. This ensures that the liftgate is locked anytime the vehicle is shifted out of park or when the vehicle is in motion.
The liftgate lock relay supply and coil sides receive a constant voltage through the battery voltage supply circuit and the ECC fuse. The normally closed contact is connected to ground and the control side is connected to the body control module (BCM). A lock function will occur when a door lock switch activation, keyless entry lock transmission, auto door lock function or a liftgate lock function has been received by the BCM. The BCM will then ground the control side of the liftgate lock relay. This energizes the relay and allows voltage to be applied to the liftgate lock actuator lock control circuit. Since the other side of the liftgate lock actuator is connected to the normally closed contacts of the door unlock relay to ground, the liftgate will lock. When an unlock function occurs the BCM will ground the control side of the unlock relay and the rear doors and liftgate will unlock.
The BCM also runs diagnostics on the liftgate lock relay control circuit and will set DTC B3825 as current and also send a Class 2 message to the DIC. The DIC will display REPLACE LIFTGATE FUSE to inform the driver that a fault has been detected in the liftgate lock circuit and that the liftgate is not locked. Faults that will set the DTC and cause the DIC to display the message could be any of the following
Power Door Locks Inoperative - Endgate/Liftgate
Schematic Reference: Door Lock/Indicator Schematics
Connector End View Reference: Power Door Systems Connector End Views
1
Did you perform the Diagnostic System Check - Vehicle?
YES - Go to Step 2
NO - Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2
Activate the door lock switches to the lock and unlock positions.
Do both rear passenger doors lock and unlock?
YES - Go to Step 3
NO - Go to Power Door Locks Inoperative
3
Did the liftgate lock actuator lock and unlock?
YES - Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
NO - Go to Step 4
4
Disconnect liftgate door lock actuator.
With a test lamp connected to a good ground, probe the door lock actuator lock circuit at the door lock actuator harness connector.
Activate a door lock switch to lock position.
Does the test lamp illuminate?
YES - Go to Step 5
NO - Go to Step 7
5
With a test lamp connected to a good ground, probe the door lock actuator unlock circuit at the door lock actuator harness connector.
Activate a door lock switch to unlock position.
Does the test lamp illuminate?
YES - Go to Step 6
NO - Go to Step 8
6
Inspect for poor connections at the harness connector of the door lock actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 10
NO .. Go to Step 9
7
Repair the open door lock actuator lock circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 10
--
8
Repair the open in the door lock actuator unlock circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 10
--
9
Replace the liftgate door lock actuator. Refer to Door Lock Actuator Replacement in Body Rear End.
Did you complete the repair?
Go to Step 10
--
10
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 2
Power was the first thing I checked. Learned the hard way to always look at it through a childs eyes and keep it simple! Its definitely mechanical because I can hear the gears ripping and it sometimes sounds like an apartment security buzzer that you have to be let in on. However, thanks for the info just the same! I knew I would have a hard time finding. No "pull a part" within 100 miles has them, so for anyone else that might read this, take note - look to shell out the $$ if you want to fix it, even if you do it yourself. Looking at $250 wholesale, 300+ retail. Next time, I'll make SURE it has a key and won't care!
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