I just bought an s2k and drove a long way home. Some codes came up on the drive

p0171-lean
p0170-fuel trim
p0131-o2 sensor low voltage

Can I assume that these three codes all will go away if I just buy a new o2 sensor? I’m not trying to throw parts at the car, but this seems like the best idea. Any thoughts?

 

Check for wiring or connector issues. But it sounds like a bad O2 sensor.

 

Sounds lean, not a bad sensor.

 

It certainly is running lean. Would a bad o2 sensor cause it to run lean? Or only cause the CEL because the car THINKS it’s running lean?

 

Have you checked for vacuum leaks yet? That is one cause of an engine running lean.

 

I didn’t see or hear any. Was considering a smoke test, but then the o2 sensor code came up and thought it wasn’t a vacuum leak

 

P0131 just means the O2 output voltage stayed below a threshold for a period of time (not that the sensor is bad). If the car has an issue causing it to run lean all the time, then that code would be set along with the lean condition and fuel trim codes (fuel trim is outside of an expected range for a period of time because the AFR issue is not resolving). So it "could" be that the sensor is bad and just stuck at low output voltage, but it could also be an actual issue preventing the car from holding good AFR. Could be that the wiring to the sensor is bad too. So there are a few things to go through to know for sure, or risk the $$ buying a new sensor.

Any running issues, smells, etc that you notice? Smoke from the exhaust? Rough idle?

Is your diagnostic tool able to show you the actual O2 voltages? AKA is the primary sensors output voltage fluctuating at all or just sitting at zero all the time? Does it change when going from not running to running?

 

I’ve got a pretty basic scanner so no. The symptoms I’m experiencing is
-rough idle (around 1k rpm but just lots of vibrations)
-acceleration bogs down past 2k rpm (until vtec)
-at idle, if I give it a tiny bit of throttle the engine will almost die

no smells

 

Sounds like symptoms of actually running lean.

If the issue was that the sensor voltage was stuck low, I would expect the car to exhibit symptoms of running very rich. The ECU would keep trying to trim the mixture more rich because the sensor keeps reading it is lean. More likely it would smell rich (strong fuel smell in the exhaust) and even black smoke from the exhaust. Could also cause rough idle like a lean condition too.

So in this case, with the rough idle, stumbling when you give it gas at idle, no smells or smoke, the sensor reading lean and the fuel trim sitting outside of normal limits for too long, it indicates an actual issue with the AFR and not the sensor just based upon the info we have here.

Now the source of the lean condition can be a lot of things. Has any work been recently done to the car that you know of?

 

Have you checked the spark plugs?

Thanks!