Hi Scotty, I have a 2003 Grand Marquis at 100,000 miles. It keeps throwing a Code # P1633 (Keep Alive Power Voltage Too Low). I had the battery terminals cleaned and tested the battery and Alternator and it is fine. What could this be. One mechanic had diagrams of the fuse box in the engine to find a short etc. No luck. Any help would be greatly appreciated. Jim Racich
Here's the PCM Pinout. Grab a straight pin and a multimeter and back probe the Yellow and Black wire going to PCM Pin 55 to check for battery voltage (Key OFF).
If you have battery voltage there, disconnect the connector and inspect the Pin and the harness female connector for heat damage or corrosion.
If you don't have power there, check the PCM/KAM fuse and make sure it's good and has power on both test tabs (Key OFF). If it has power then you can either trace the yellow and black wire back from the PCM to the fuse box (to find the break in the wire) or just run another FUSED wire from battery positive and splice it to the yellow and black wire at the PCM.
