One would first need to test the HUD, the HUD dimmer switch, related wiring as well as the IP Cluster fuse. One of these items could be faulty. Another item to check for is the wiring harness around the A?C accumulator. The wiring harness on the 97-03 Grand Prix was known to rub out and ground against the metal accumulator, causing electrical concerns including those you mention. Repair the harness and make sure it is snug. Insulate it to protect from further damage.
I am 99.9% sure that it is the light sensor located on the HUD board. I had this same problem several times - simply requires removing the board and re-soldering the sensor. There is a great write up out there with step by step instructions on the web, check grandprix.net or do a search for fixing the Heads up display light sensor.3Courtesy of MACCPGP.com
Replacing the HUD Photodiode
by Bill Whitmer
Medium to Large Philips screwdriver
Very Small Flat Head screwdriver
T-15 Torx Bit or Driver
25w or less (not more!) Soldering Iron, with fine tip
Vacuum Desoldering Tool
Drill with 15/32" Bit
Small needle nose pliers
Very small amount of 1/8" diameter head shrink tubing.
2x PDB-C142-ND from www.digikey.com wired in series works well (these look like LED's but they aren't). They are $1.50 each. PDB-V106-ND appears to be almost identical to the original, but it is
a $7 non-stock item with a minimum order quantity of 8.
This write up is for cars where the HUD photodiode is bad and the
resoldering technique doesn't work.
Step 1: Remove HUD Pod from Dash
This can be done by raising the front of the HUD pod by about 1" then
pulling forward to release the quick clips. The quick clips can be tricky
to remove without losing them in the dash. The security LED and auto
headlight sensor simply twist out of their holder.
Step 2: Remove HUD from Dash
First unplug the blue connector from the left side of the HUD module.
Next remove the two Philips screws on the HUD module on the side closest
to the engine bay. The HUD should come out by pulling up on the side
closest to the steering wheel, it still has two quick clips holding it
down. Be careful not to scratch the dashboard when removing the HUD.
Step 3: Disassemble the HUD Module
Remove the four Torx T-15 Screws from the Top of the HUD Module. Remove
the ribbon Cable from the PCB, and the maroon two wire connector also.
Remove the PCB by pushing up on the two clips.
Step 4: Remove the Photodiode
Make sure the soldering iron is at full temperature. Desolder the joints
on the photodiode by heating them up with the soldering iron until they
melt, and using the vacuum desoldering tool while the joint is liquid.
Place the small flathead screwdriver between the photodiode and the PCB.
Again heat up each joint on the photodiode, and use the screwdriver to pry
the photodiode loose. Pry only a small amount on one joint at a time
until the photodiode comes loose, in order not to damage the PCB.
Step 5: Join the new photodiodes (only if using 2 PDB-C142-ND's in series)
The reason to use two photodiodes in series is that these only output .5v,
and the original photodiode outputs 1.00v, the original part number is
BPW21 from Vishay Semiconductor or Infineon, but I have been unable to
find a supplier for this part. Cut the positive (long) leg on one of the
new photodiodes, and cut the negative (short) leg on the other. Cut both
to about 1/4" long. Bend both cut legs 90 degrees. Solder the two cut
legs together. Cover the solder joint with a small amount of 1/8"
diameter heat shrink tubing. Cut the remaining two legs on the
photodiodes to about 1/4". It is very important to remember which one is
positive (originally long) and which one is negative (originally short.
Bend the remaining legs to match up with the photodiode holes on the PCB.
Step 6: Attach the new photodiodes to the PCB
You will need to remove the coating on the PCB where you will be
soldering, it cam be easily scraped off. Melt a small amount of solder in
the holes where the original photodiode was soldered, on the bottom (no
components) side of the PCB. The hole that is closest to the edge of the
PCB is negative, the innermost hole is positive. Attach the photodiodes
by placing the correct leg of the new photodiodes against the correct
hole on the top side of the PCB, and applying heat to the bottom side of
the PCB to melt the solder. Make sure the joint is good.
Step 7: Modify the top HUD module cover (only if using 2 PDB-C142-ND's in series)
The new photodiodes won't fit through the hole on the top cover for the
HUD module. Simply drill out the hole, I used a 15/32" drill bit.
Step 8: Reassemble everything
Put the PCB back in the HUD module, reconnect the two connectors, and
screw it back together. Put the HUD module back in the dash, reconnect
the connector, and put the two Philips screws back in. Now is a good time
to see if the HUD works properly. Replace the HUD pod, first reattach the
auto headlight sensor and security LED, the HUD pod simply presses into
Enjoy having a working HUD again!