Continuouse Check Engine Light

[jmcbeath1]

The check engine light on our 2006 Terraza with 132,000 miles starting coming on intermittently in Jan. 2014. Our local shop got a code 171 lean on vacuum leak check and replaced the 02 Sensor and air filter. The check engine light reappeared. He suggested we take it to a larger shop which could perform a smoke test because the leak was so small he could not find it. In May the new shop replaced the Oxygen Sensor. Light came back on within 3 miles! In June, back to local shop which replaced the MAF sensor and cleaned fuel injectors. Light back on again. In the meantime, we noticed that the fuel gauge didn't seem to be showing the fuel level accurately and the MPG indicator seemed to be indicating a significant drop in the mpg . So we started calculating the mpg the old fashioned way and it was showing around 20 mpg which is what we usually have. Now we are wondering if the problem could be the fuel level sensor which on one of the sites I visited said, in addition to giving a faulty fuel level reading, could also cause the check engine light to come on. On Monday, we also had what may be an unrelated problem, but I don't want to leave out something that may be relevant-the car sputtered, before it started on a long trip we were taking. Then the acceleration started really dragging when we had to accelerate from a stop. We bought some fuel additive, and by the next day, the problem was gone. So it could just have been bad fuel. Both shops are at a loss to determine why the check engine light is still on and don't want to do anything else that doesn't work and suggested we take it to a dealer. But before I spend any more money, I am seeking any similar experience other members may have had like this and what the resolution might be. Thanks.








Thanks.

[maxwedge]

Lean condition,low fuel pressure,dirty injectors,vacuum leaks, any air getting in behind the maf are the most common causes, clear the codes and see if it comes back.

[Tech II]

What is the exact code?

[jmcbeath1]

re: maxwedge response: Thanks, but the tech cleared the codes several times, the last time being last week. No luck.

re: TechII response: Thanks. The only code I was given was 171 lean. I'll check and post it when I get it. .

[Tech II]

OK, P0171 means that you have a lean condition......a scan tool would show O2 data below 0.452 volts.....and it it would show the PCM trying to compensate, with fuel trims above 0%(0 % is the ideal reading the PCM wants to attain...may fluctuate slightly above and below, but with a lean condition can go up to plus 20 %)....

Any good tech, would put the scanner on the vehicle, clear the code, and take a snapshot of O2 data and fuel trims, while on a road test.......

So, what could cause this code? Naturally, a vac leak......an exhaust leak, just ahead of the sensor, dirty fuel filter(last time it was changed?), bad injector, etc.

Bad gas can cause this, if it has water in it..something like drygas would help...

One other thing is the MAF sensor.......while observing O2 data, if the data is lean, then disconnect the MAF sensor......if the lean condition is now corrected by disconnecting the MAF, you probably need an MAF....