2003 Alero, heater won't shut off? Fan shuts off but can't turn heater off.

SOURCE: I HAVE A 99 ALERO OLDS.4CYL.& IT WON'T PASS SMOG

IF DECELERATION FUEL REDUCTION SYSTEM IS NOT OPERATING, FUEL ECONOMY WILL BE REDUCED WHILE HC AND CO EMISSIONS ARE INCREASD.SEE ON MANY ENGINES WITH DECELERATION FUEL REDUCTION SYSTEMS THE PCM STOPS GROUNDING THE INJECTORS IN A SPECIFIC RPM, DURING DECELERATION.

SOURCE: 2003 alero dash light won't shut off

I had the same problem in my 03 alero. I turned the key into the on position pressed the gas peddle down 3 times and it went off and hasn't been on for over a month.

SOURCE: shutting down

Try replacing the air filter.

SOURCE: Why won't my car heater shut off

You have a short in the switch or resistor pack. replace the switch

SOURCE: 2003 Olds Alero heat will only work on High

It is the blower motor resistor