1997 Plymouth Breeze CHECK ENG. LIGHT

P0112 - Intake Air Temperature Circuit Low Input
P1496 - 5 Volt Supply Output Too Low
P1599 - A/C Pressure Sensor Volts Too Low

Since no one has come up with a better answer yet, start by unplugging the intake air temperature sensor, then measure the voltages on the two terminals with the ignition switch on. This is normally not a valid test for this circuit because the readings will be wrong, but in this case code 112 refers to its signal wire being grounded. Proof of that is you'll find 0.0 volts on the signal wire and the normal 0.2 volts on the ground wire which is shared by a number of other sensors. Anything less than approximately 0.5 volts on the signal wire will set this code.

Code 1496 doesn't specify at what voltage the code will set, but typically that 5.0 volt supply is real stable. If it is indeed a little low, there's no telling at what voltage other circuits will start setting their own codes. Given that all three codes refer to that 5.0 volt supply, tell me what you find there. If you find exactly 5.0 volts, you'll most likely be looking for an intermittent problem. It would be real helpful if you could fashion something that lets you watch the voltmeter inside the car while you're driving so you can see when it acts up and what might related to it.