Diagnostic Aids
The 5-volt reference for the TPS is the same 5 volts used by the A/C pressure sensor. If the 5-volt reference has a short to ground, the MAP sensor, A/C pressure sensor and other related sensors will also have a short to ground. This short to ground will not damage the PCM. When the shorted 5-volt reference circuit is repaired, the PCM 5-volt reference will return to normal.
In extremely low temperature climate, the A/C pressure signal can drop as low as .3 volt. If this happens, Code 66 will set and disable the A/C system. Clear code and recheck A/C system in a heated garage to determine if outside ambient temperature is cause for Code 66 setting.