DTC P0171, have you had it ?

I have not had the DTC error P0171 myself.

The actual description is "system too lean (bank 1)", no lean in the bank. "Too lean" means that the air-fuel mixture has too much air in relation to the amount of fuel being delivered.

A factory service manual will have a chart that outlines the possible causes of any particular condition and so is a very valuable tool.

A possible cause for a lean condition on only 1 bank is a poorly performing oxygen sensor. A faulty EGR valve can also cause the condition but that tends to be on both banks, not just one.

A vacuum leak would also probably cause rough idle or poor performance as well. A simple way to check for a vacuum leak is to attach a vacuum gauge.

thanks RayO. I may diagnose this myself so your suggestions are appreciated, do you know what i will pay for a decent vacuum gauge, and where could i get one?

You're welcome!

You should be able to get a vacuum gauge at any decent auto parts store or Sears for under U.S. $40.00. As I mentioned before, if you do not have a rough idle or loss of power, then a vacuum leak is not very likely.

I just thought of something else that can make the engine run lean... Check the air intake hose from the air filter back to the manifold for cracks. To do this properly, you will have to remove it from the engine compartment to check the underside. This is easy to do and won't require any special tools. A crack between the air flow meter and the intake plenum would suck in extra air, making the air/fuel mixture too lean. If you find a crack, you can apply a bead of oxygen sensor-friendly RTV (room temperature vulcanizing) caulk to the crack and then apply duct tape over the bead. Make sure the stuff you use is O2 sensor-friendly or you will eventually ruin the O2 sensor.

thanks again, i will perform the check on the air intake hose.

by the way, i just changed the oil and the light hasnt yet come back on, so i may see how this goes for the next few hundred miles. i wonder if that was the problem...

You're welcome!

Some items have 2-trip detection logic, which means that the malfunction has to be detected in 2 consecutive trips, where a trip is defined as starting the engine, driving for a certain amount of time for a certain distance. If the light does not come back on, don't worry about it.