Q: When the AC is turned on my Check engine light comes on , code reading throttle position sensor, not enough voltage.

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Only when I run the AC the check engine light pops up along with the triangle with exclamation point , code reading throttle position sensor/ not enough voltage and the cars RPMs fluctuate and car runs really weird. I reset the computer by hooking it up to a code reader. As long as the AC is not running, car runs fine. What could this possibly be, I changed the sensor and bought a new higher voltage battery being that I have 2 amps to my stereo . Tested it again by turning on the AC, same result

My car has 120000 miles.
My car has an automatic transmission.

If you have the electronic type throttle that has no cable to the throttle body, then you will need to check to make sure that battery voltage is not dropping below 12.5 volts when your A/C is turned on. You will need to have the charging system checked to make sure it is putting out above 13.2 volts at idle and the amperage at 1500 is within specified range of 87 amps and that the voltage does not drop below 13.5 with no load.

You may be overloading the alternator with the stereo amps you have and causing the battery voltage to drop too low at idle causing the throttle actuator to not work correctly. The A/C takes about 20 amps of power to run and if you are already taking more than the alternator can put out at idle, then the only place to get the power is from the battery. The battery is rated in AMPs not volts. You put a heavier duty battery that has more amp capacity and if the alternator cannot replace the power taken away, then the voltage will drop in the battery until it gets below the 12 volts needed to power the electronics in the car and there’s where you will start to have problems. If you want to have this diagnosed in person, a technician from YourMechanic can inspect your Check Engine Light and let you know exactly what will need fixing.

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