In this Instructable, I will show you how to repair odometer/gear select (PRND321) LCD on your GM truck. In this case, mine is a '02 Chevrolet Avalanche but this should apply to all GMT 800 series trucks within this age range.
A common fault on '99 - '02 GM trucks was the permanent or intermittent failing of the odometer/gear select LCD. This meant that you were unable to see what gear you were currently in, unable to determine the mileage of the vehicle, and unable to use the trip computer. The problem was caused by poor soldering of the internal components. Here's how to fix it…
Step 1: Determine the Fault
Before starting anything, check that the "message center" is operational.
If both the odometer and message center are not working, the problem is likely to be a fuse (both of these displays share the same fuse.) The fuse in question is the IGN 0 fuse (responsible for "PRND321/odometer/VCM/PCM") which is located in the instrument panel fuse block on the driver's side edge of the dashboard (the edge which you can only access with the driver's door open.) Open it up, replace it, and see if that cures the problem.
If the message center display is operational, but the odometer display is not, read on…
Step 2: Obtain Access to the Instrument Cluster
First off, engage the emergency brake. You will be moving the column shift out of park, so this will prevent the truck from moving/rolling.
Insert the key into the ignition and turn to "ON" - you don't have to fire up the truck, but you will need to turn the key enough that you can move the gear stick down to the lowest position.
Using the steering wheel's height adjustment, move the steering wheel to the lowest position.
Finally, remove the dashboard surround. This simply pulls off, and requires no tools.
Step 3: Removing the Instrument Cluster
The instrument cluster is held in place by four (4) 7mm hex screws, one in each corner. Remove these.
Tilt the instrument cluster forward carefully, and unlatch the large wire harness on the back. The instrument panel can now be removed.
Step 4: Opening Up the Instrument Cluster
Remove the black panel on the back by loosening the clips.
You will now be looking at the back of the printed circuit board (PCB). Carefully pry the board away from the instrument cluster - it is held in place only by the pins of the stepper motors (labelled on the image)… but BEWARE, there is another small wire harness on the right and side of the board.
The last thing is to gain access to the back of the LCD panel. It is held in place by nine (9) pins and three white clips. Gently unhook the three clips, and bend back the display enough that you can get to the back of the LCD where the pins are connected. (See pictures to explain this step better)
Step 5: Soldering
Check the connections for the any dry joint - as you can see, the offender is the pin on the end in my case (apparently, it's usually this pin). Crack out the soldering iron and solder the joint securely. Try not to burn the plastic around the edges.
I'll hold off on the "after" picture because my soldering is embarrassingly poor!
Step 6: Put It All Back Together
Bend the LCD display back carefully, ensuring that you have hooked in all three white clips.
Reconnect the small wire harness between the PCB and the instrument cluster.
Lining up the pins of the stepper motors with their corresponding sockets on the PCB, push the board back onto the instrument cluster. Put pressure on the back of where the stepper motors are (see photo).
Replace the back plastic cover of the instrument cluster, ensuring all clips are secured.
Step 7: Put It Back in the Truck
Connect the large wire harness on the back of the instrument cluster. Line up the instrument cluster and replace the four (4) hex screws.
Replace the dashboard surround - lining up the pins helps with this (see photo)
Step 8: Fire It Up!
Fire up the truck, and you should see the odometer/gear select (PRND321) LCD display working perfectly.