What is PO496 code? I've got a PO171B also, which I'm assuming is dirty an O2 sensor.

Question edited for clarity and add CAPS.
Question move to Cobalt category.

It is dumping extra fuel.

P0171 code SS SC - Cobalt SS Network

CobaltSS.net https://www.cobaltss.net > forums > p0171-code-ss-sc-...
Mar 1, 2014 - P0171 is a fuel trim lean code. Meaning the car is having to add more than 25% of the normally asked for fuel to reach proper O2 sensor ...

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P0171 Chevy Cobalt: Fuel Trim System Lean Bank 1

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‎Definition · ‎Symptoms · ‎Causes

Hey Eric,here's a link on how to remove codes if you haven't already done it this way.

The code is for the heater circuit in the front O2 sensor.
The sensor and circuit would need to be tested.

What is a CO sensor? Never heard of it. a 1999 OBD2 ford has approximately 1600 possible fault codes most of which can turn on the light. If you dont know which one is turning it on, you are guessing randomly which is expensive and usually unsuccessful. get the code(s) and then diagnose the possible causes. The vehicle you list (99 4L explorer) rarely had injector problems. Much more common were EGR sensor(DPFE) sticking at voltage, evap problems, misfires, and lean conditions due to dirty MAF, or vacuum leaks. get the fault code, or you will not fix the problem.

code p 0496 refers to evaporative emission (EVAP) system---high purge flow===causes ---wiring --EVAP valve---mechanical fault

code p 0171system too lean bank 1===causes --intake / exhaust leak---AIr system---MAF/VAF sensor--fuel pressure too low/---pump--injectors ---Heated oxygen sensor (HO2S)

with the first code it could be a faulty vent valve or solenoid
with the second code , it is probably a faulty HO2S unit ( the one in the exhaust manifold before the cat converter)

o2 sensors get dirty and trip the check engine light they get carbon buildup on them.

P0171 is O2 sensor indicates lean. You probably have a vacuum leak. The most likely and common cause is the PCV elbow at the front of the engine.

your purge valve solinoid isnt closing properly so just take it out and clean it and reset the fault code

PO171b System to lean,( to much air not enough gas) check for vaccum leaks if ok then i would have oxygen sensor checked,most of the time it a bad o2 sensor (oxygen sensor) hope this helps good luck.