P1246 - Generator Load Input Failed (All Others) The PCM monitors generator load from the generator/regulator in the form of frequency. The frequency range is determined by the temperature of the voltage regulator where 97% represents full load, below 6% means no load. Generator circuit short to GND
Generator circuit short to PWR
Generator circuit open
Generator drive mechanism
Damaged generator/regulator assembly
Verify battery voltage is 14.5V.
Verify generator/regulator has the correct part number.
To me that sounds like 1 of a couple possibilities.
A. You have underdrives are are not tuned for them. Though I don't think that really happens, possible though I'd think.
B. The alternator is not making a good ground to the block. Corrosion or maybe a lackluster engine ground.
C. The "alternator clip" has failed or is failing. --> Alternator Clip "How-To"...
C. would be my best guess as it makes the most sense to me.