2006 Camry P0171…

[jcountry]

This has me confused.

Keep getting a P0171 on this 4 cyl 2006 camry.

Mechanic thought it was downstream O2, but keeps coming back.

So, I ran some live data.

Long term fuel trim is ridiculous. Gets much worse under load.

Short term is exactly the opposite. Been going as far as 10% negative under load

Any ideas what could cause this?

 

[ExplicitBoricua]

Of not wrong, if it was the O2 (and probably the catalytic converter) if would have been code PO420. Just saying as I just had to the converter and O2s on my car.

That PO171 could be the mass air flow sensor. If it’s not that, it could be a vacuum leak in the system, and I’d recommend to just bite the bullet and have a smoke test done. Hope it helps.

 

[canut]

+1 with above post...

Your MAS of 3.8 lbs per min (28.7 grams/sec) is three times normal for an idling car. Is your MAS reading 0.0 when engine off key on ? What is your MAP reading (vacuum), w/engine off key on it s/b 100 (atmospheric pressure of 30) and w/engine at idle somewhere in the 30-50 (about 15 lb vac) range and drop as throttle is applied. Running readings are engine dependent for each engine so I can't talk exact numbers for your setup.

What was status of car when you took these readings. Can you provide RPM and upstream O2 (pre CAT) B1O1 reading, it s/b swinging between 150mv and 770mv. The down stream O2 (after CAT) reading B1O2 s/b a steady voltage of about 1 volt and it is not used for fueling so it should not have anything to do w/trims being way off, normally signals bad cat or sensor for the emissions verification check only..

Your engine temp is at 190, was the car just started up, is that your normal temp it seems cool. The O2 (pre CAT) is used for fueling after car is hot, prior to that PCM is running in open loop using the LT trims stored in PCM from previous runs (that's the main use of LT trims) they are not used after engine is hot (closed loop/ O2 ready). Does you scanner display CAT temp it s/b above 600 degrees for correct pre and after CAT O2 readings.

 

[jcountry]

+1 with above post...

Your MAS of 3.8 lbs per min (28.7 grams/sec) is three times normal for an idling car. Is your MAS reading 0.0 when engine off key on ? What is your MAP reading (vacuum), w/engine off key on it s/b 100 (atmospheric pressure of 30) and w/engine at idle somewhere in the 30-50 (about 15 lb vac) range and drop as throttle is applied. Running readings are engine dependent for each engine so I can't talk exact numbers for your setup.

What was status of car when you took these readings. Can you provide RPM and upstream O2 (pre CAT) B1O1 reading, it s/b swinging between 150mv and 770mv. The down stream O2 (after CAT) reading B1O2 s/b a steady voltage of about 1 volt and it is not used for fueling so it should not have anything to do w/trims being way off, normally signals bad cat or sensor for the emissions verification check only..

Your engine temp is at 190, was the car just started up, is that your normal temp it seems cool. The O2 (pre CAT) is used for fueling after car is hot, prior to that PCM is running in open loop using the LT trims stored in PCM from previous runs (that's the main use of LT trims) they are not used after engine is hot (closed loop/ O2 ready). Does you scanner display CAT temp it s/b above 600 degrees for correct pre and after CAT O2 readings.

I’m gone for a few days, but I’ll track that stuff down when I get back.

I’m perturbed that the shop didn’t feally check any of this out.

Good mechanics are hard to find

 

[jcountry]

I actually remember that the MAF didn’t go to 0.0 with the engine off.

I figured maybe it was just the last bit of data from the live stream.

Maybe the MAF sensor is bad? (I cleaned it, but I guess it could fail internally.)

 

[canut]

Following is some generic fuel injection basics, not Toyota specific.....

Not sure of what type Toyota used in 2006. There are two general types but both work similarly. They either us a wire or a thin film strip that is heated. As air passes the heated element it is cooled and the voltage and/or current changes (depending on design). The PCM monitors the changes and converts the voltage or current reading to air volume and then converts that to weight (grams per second), that's used to control injector duration and insure correct fuel burn. trivia...14.7 grams of air to 1 gram of fuel (14.7 to 1 is 100% gasoline, changes for alcohol %) gives a burn that should produce ST trims at 0% usually never see 0% most likely +/- 10% as engines mechanical tolerances are not perfect however over 20% trim correction throws a DTC.

Hopefully you cleaned it MAF(MAS) cleaner, not carb or other stuff. The innards are pretty sensitive and can be damaged by touching and/or harsh chemicals.

 

[jcountry]

Following is some generic fuel injection basics, not Toyota specific.....

Not sure of what type Toyota used in 2006. There are two general types but both work similarly. They either us a wire or a thin film strip that is heated. As air passes the heated element it is cooled and the voltage and/or current changes (depending on design). The PCM monitors the changes and converts the voltage or current reading to air volume and then converts that to weight (grams per second), that's used to control injector duration and insure correct fuel burn. trivia...14.7 grams of air to 1 gram of fuel (14.7 to 1 is 100% gasoline, changes for alcohol %) gives a burn that should produce ST trims at 0% usually never see 0% most likely +/- 10% as engines mechanical tolerances are not perfect however over 20% trim correction throws a DTC.

Hopefully you cleaned it MAF(MAS) cleaner, not carb or other stuff. The innards are pretty sensitive and can be damaged by touching and/or harsh chemicals.

Yep.

Used MAF cleaner.

I’m gonna try again tomorrow.

This whole issue started not long after I changed the air filter. I’ve been looking closely for hoses or fitting that are cracked or loose and haven’t found anything yet.

 

[ExplicitBoricua]

Lol, you jinxed me. Just got the dam code on my daughter's 07 Matrix this morning. Guess we're figuring it out together.

 

[jcountry]

Lol, you jinxed me. Just got the dam code on my daughter's 07 Matrix this morning. Guess we're figuring it out together.

This car has been rock solid.

Until this code....

I wish the mechanic would troubleshoot properly. They kept it almost a week each time...

Tired of spending money on bozos who have no idea what they are doing.... I think if I take it back, they will just throw more parts at it, without really diagnosing.

 

[ExplicitBoricua]

This car has been rock solid.

Until this code....

I wish the mechanic would troubleshoot properly. They kept it almost a week each time...

Tired of spending money on bozos who have no idea what they are doing.... I think if I take it back, they will just throw more parts at it, without really diagnosing.

I’ve spent less on this 07 Matrix than I’ve already dumped into my ’17 Dodge Journey... The Matrix will die with us!