long term fuel trim

I'm trying to diagnose a p0171 error code.

I've got an actr1. install the scan tool

  1. start and idle engine at normal operating temperature in the Closed Loop
  2. record the data for long term fuel trim
  3. turn off engine
  4. turn on ignition, engine off
  5. review freeze frame / failure records and record displayed data for this diagnostic trouble code

how do I get it in the Closed Loop? how do I get the data for long term fuel trim in the scanner? how do I view freeze frame / failure records in the scanner?

thanks.

Reply to
Raymond
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"Raymond" wrote in news:be_Ve.20$ snipped-for-privacy@news.uswest.net:

"Closed-loop" occurs when the ECM sees that the coolant temperature is at

90C (194F), and the throttle is NOT wide open.

If the engine is less than full-warm, you run the risk of dropping to open- loop, which is when the upstream O2 sensor is not used as ECM input.

Reply to
TeGGeR®

P0171 means Bank 1 system too lean.

Closed Loop means the O2 sensor is heated up to operating temperature and is providing signals to the ECU. To get it to closed loop, drive the car for about 5 minutes or so.

Simple OBD II scanners do not have the capability to provide fuel trim or freeze frame information. Scanners with that capability tend to be in the thousands of dollars. The ones they lend out at auto parts stores are under a hundred dollars.

What kind of vehicle are you trying to diagnose? Are you sure there was only 1 trouble code? Was there a code for O2 sensor or MAF sensor? A marginal O2 sensor or MAF sensor can cause this code.

Reply to
Ray O

so I just warm up my car then to get to the closed loop?

will my scanner tell me if I'm in closed loop?

Reply to
Raymond

Yes, but at idle, not with the throttle floored.

Probably not.

Reply to
Ray O

I figure out the bank 1 system too lean.

it's actually for a nissan pathfinder. I've been reading this group for a while and noticed there are quite a few knowledgeable people around here that can help me.

I've reset the light 3 times. 1st time, I just got P0171. 2nd time, I got P0171, bank 2 system too lean. the 3rd time, just P0171.

I looked at the MAF sensor, and it looked ok. no tools to test.

stupid car has 4 oxygen sensors. 2 were already replaced which were by the catalytic converter. the other 2 are right by the engine. how can I test if the oxygen sensor is bad?

Reply to
Raymond

If it is a heated wire system, make sure the wire isn't coated with gunk.

4 O2 sensors is common on a V6 or V8 engine. A properly functioning O2 sensor in closed loop mode will send an on-off signal to the ECU. You may try google to see if you can come up with the proper voltage and repetition rate.
Reply to
Ray O

it's not a heated wire.it's plastic with some electronics in the middle.

so can the $150 dollar scanner I have tell me if one of my O2 sensors is bad?

Reply to
Raymond

I'm not familiar with Nissan so I'd have to look at it to see how it works. There are basically 3 ways to measure how much air is getting into the engine:

1) A mechanical flap or vane that moves more as more air flows past it. 2) A heated wire that gets cooled more as more air flows past it. 3) An optical system that is kins of like those burglar alarms that shine a light at a target. The light is reflected off a mirror that is mounted on a filament in the air stream. The more air flows, the more the filament and mirror are disturbed and so the light detector counts the disturbances.

Yes and no. The scan tool will know if the O2 sensor is inoperative or has an open or short circuit but it won't tell if the O2 sensor's performance is marginal, especially if it is like the Actron scan tool I have. You'll need a digital volt/ohm meter for that.

Reply to
Ray O

Geez, what a pain. I don't know what sort of tool you're working with, but to diagnose this you will need the capability to access the 'data list' from the computer. If you are using a scanner that just serves as a code reader, than that won't cut it. Anyway, the reason you need to see the data list is to observe fuel trim #s, and also the input voltages from the 02 sensors. But, barring an expensive scanner, you could observe the voltage of the sensor directly from the sensor with a good meter or logging scope. I've had to do that a few times, and it works. The sensors cycle between .2v (lean) to .8v(rich), but the frequency varies from manufacturer to manufacturer.

Reply to
qslim

I think what I have is the optical system.

I guess if I have problems with my O2 sensors, looks like the performance are marginal? If I get lucky, will it will me which O2 sensor it is?

If not, I guess I'm stuck to bringing it to a mechanic.

temperature

Reply to
Raymond

If the O2 sensor quit working altogether, you would have a trouble code for it. An O2 sensor that is getting ready to fail might not set a trouble code.

If I get lucky, will it will me which O2 sensor it is?

If the O2 sensor fails altogether, the scan tool will tell you by the code, i.e. bank 1 sensor 1or bank 1 sensor 2 or bank 2 sensor 1 or bank 2 sensor

  1. If the O2 sensor hasn't completely failed, then you're out of luck.

If you invested in a scan tool, you might want to invest in a basic digital volt/ohm meter. You can get one at an electronics shop like Radio Shack for under $50. Then do a google search on measuring O2 sensor performance and you can tell for sure.

Reply to
Ray O

it's actually a loaner tool from an auto parts store.

the two O2 sensors, if they're the ones that are bad, are a bit difficult to get to.

I guess I'll take it to a mechanic.

thanks for all your help.

performance

Reply to
Raymond

You're welcome!

Good luck.

Reply to
Ray O

"Ray O" wrote in news:a8619$432887e4$44a4a10d$ snipped-for-privacy@msgid.meganewsservers.com:

The latest method is TFT, which is exactly as the OP describes it. Apparently that's less prone to contamination than the other methods.

More here:

formatting link
may help the OP determine the cause of his problem.

Reply to
TeGGeR®

Great info TeGGeR!

Reply to
Ray O

Perhaps in talking about Bush. We don't seem to talk about CARS too much anymore... ;)

Reply to
Hachiroku

As the code is telling you bank 2, I'd rule out the MAF sensor at this time, concentrating on the 02. You need a scanner that will tell you live "data" so you can see what is working. You can watch the 02 sensors and determine what is going on.

Reply to
Steve H

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