P0 171 Error Code

[pfrontin]

99 1500, 360cid, AT, 4x4.

When the exhaust gets hot (usually on long trips) it idles very rough and the check engine light comes on. I borrowed an OBDII scanner from the local Chief Auto Parts and it returned error code P0171:

"A lean air/fuel mixture has been indicated for fuel system 1/1 by an abnormally lean correction factor"

I just tuned the truck up (cap, rotor, plugs, oil & air filters, etc.), and just had the cat replaced. The timing appears correct? (around 5 degrees advanced, but I don't have a manual so I'm guessing based on other V-8's I've owned in the past). The truck runs fine on cooler days; I just drove it 120 miles this morning- no problems.

Does anyone know exactly what this code means? Is it the front O2 sensor reading wrong, and telling the computer to compensate in the fuel mix?

[moparmike70]

It sounds like the heater circuit on the 1/1 O2 is bad. This may happen intermittenly, causing the computer to think the engine is running lean. I would replace the O2.

[hundahunta]

does the vehicle have an exhaust leak!!

[pfrontin]

No exhaust leak...just had the cat replaced, it was clogging.