V-6 Check Engine P0171 & P0420 trouble codes

5 Speed · #1 (**permalink**) 08-24-2004, 10:34 PM

I just finished a 19K trip to Alaska and during the trip I had the check engine light go and off three or four times and it finally stayed on. Checked with a reader from Autozone in Fairbanks and it had two trouble codes P0171 System too Lean (Bank 1) and P0420 Catalyst System Efficiency Below Threshold (Bank 1). I think I will try and start with cleaning the A/F sensor can you check the heater circut on a O2 sensor? The flow chart in the repair manual isn't specific. Anyone with a V-6 tackled this before? I found some P0171 when I did a search but the P0420?

mustang67408 · #2 (**permalink**) 08-30-2004, 09:16 AM

Quote:

Originally Posted by 5 Speed

I just finished a 19K trip to Alaska and during the trip I had the check engine light go and off three or four times and it finally stayed on. Checked with a reader from Autozone in Fairbanks and it had two trouble codes P0171 System too Lean (Bank 1) and P0420 Catalyst System Efficiency Below Threshold (Bank 1). I think I will try and start with cleaning the A/F sensor can you check the heater circut on a O2 sensor? The flow chart in the repair manual isn't specific. Anyone with a V-6 tackled this before? I found some P0171 when I did a search but the P0420?

Most of the time cleaning the MAF sensor will take care of the p0171 code.
The P0420 is usually a bad cat converter. They become inefficient and do not register properly thru the rear o2 sensor. The cat/cats are 8yr/80k mileage warranty.
I would take it to the dealer and have it looked at and replaced. If you have more than 80K miles. Have it replaced anyway, it will eventually cause problems. Most reputable exh shops have replacement cats at a reasonable price.

5 Speed · #3 (**permalink**) 09-07-2004, 04:43 PM

Had a can of electrical contact cleaner. I can't believe how dirty the two small electrodes were inside the Mass Air Flow sensor, with two or three squirts from the cleaner and they were half the size. Started the truck up and the Check Engine light is off!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I think I will clean the sensors more often!

mustang67408 · #4 (**permalink**) 09-07-2004, 05:01 PM

Go 5speed, Go 5speed, Go 5speed

(dancin)

czarny · #5 (**permalink**) 11-11-2004, 11:39 AM

5Speed and Mustang,

Thanks for the help! MAF was also the culprit on my MIL P0172. Followed 5Speed's procedure and Mustang's diagram and had my 2000 5Spd TRD Tundra back w/o the Check Engine light! Now onto reading some of the modification posts for pleasure

BJ

Bubba17 · #6 (**permalink**) 04-26-2005, 10:52 PM

Troubleshooting diagram? Help a brother out! Had the P0171 code a few months ago. Cleaning the MAF sensor worked like a charm. Light stayed out for a few months, now it's back on with P0420 code. Any way to check voltage on the O2 sensors before I replace the cat? Inspection is due in May and they check OBD here in NC. Any help will be appreciated!

mustang67408 · #7 (**permalink**) 04-27-2005, 12:39 AM

What vehicle are you working on? Is it your 04 Tundra? I need this info before i can help you with
the O2's.
P0420 is usually always the CAT CONV. "LOW EFFICIENCY"
It's not cleaning the exh up as well as it should.
How many miles on it? shouldnt be under warranty?
let us know
Thanks

Bubba17 · #8 (**permalink**) 04-27-2005, 02:26 PM

Oops, sorry. No, it's for the wife's 99 4Runner with V6 (5VZ-FE) with 80k+ miles on it. I realize it could be near end of life for the original cat, but it seems fishy that I just had the P0171 code a few months ago, and I'm seeing that code mentioned along with the P0420 code in the same discussion. Thanks for your help.

mustang67408 · #9 (**permalink**) 04-27-2005, 02:46 PM

Quote:

Originally Posted by Bubba17

Oops, sorry. No, it's for the wife's 99 4Runner with V6 (5VZ-FE) with 80k+ miles on it. I realize it could be near end of life for the original cat, but it seems fishy that I just had the P0171 code a few months ago, and I'm seeing that code mentioned along with the P0420 code in the same discussion. Thanks for your help.

With the p0171 the engine usually ends up running LEAN.(MAF PROBLEM USUALLY)
Lean=BAD. The engine and exhaust tend to be HOTTER and sometimes under the right conditions will COOK the CAT.The NOX (Oxides of nitrogen) This is what causes SMOG when mixed with sunlight. The NOX emmissions go up when engines run hotter and combustion temps increase. Therefore making exh temps increase and this is what cooks the cat.
Pm me your e-mail and ill send you some more info. Or i can try to attach it here.
I also need to know if it is CALIF SPEC or Fed. It will say on the sticker under the hood.
Thanks
Victor

Bubba17 · #10 (**permalink**) 04-27-2005, 09:38 PM

Sticker says it complies with 1999 California and US EPA NLEV requirements.

mustang67408 · #11 (**permalink**) 04-27-2005, 11:14 PM

Try these attatchments and see if this is wha your looking for. These are for NON CALIF emissions. The non calif uses 02 sensors, The Calif uses AIR FUEL SENSORS. They are different but do the same job. The A/F sensors are a more precise measurement.
Let me know
Victor
PM the VIN and I can check to make sure it isnt a calif vehicle, I am fairley certain it isnt.

Bubba17 · #12 (**permalink**) 04-28-2005, 07:10 PM

Thanks for the files. This should be more than I need. I don't have a scope and only the basic $100 code reader, so I can't check waveforms, but I'll definitely check the resistance on the O2 sensors this weekend.

bayou39 · #13 (**permalink**) 04-29-2005, 12:28 PM

I have the po171 trouble code as well.
I tried cleaning the maf sensor and it is still on.
When I started it up and drove away, it was extremely boggy like something was really holding it back. It will not idle right at all, sounds like its going to stall. When i am cruising it is fine. Anyone had this problem as well ?

mustang67408 · #14 (**permalink**) 04-29-2005, 12:35 PM

Quote:

Originally Posted by bayou39

I have the po171 trouble code as well.
I tried cleaning the maf sensor and it is still on.
When I started it up and drove away, it was extremely boggy like something was really holding it back. It will not idle right at all, sounds like its going to stall. When i am cruising it is fine. Anyone had this problem as well ?

Replace the MAF sensor. Make sure there isnt a piece of debris in it.
Here is a attachment to help you check the MAF SPECs. 9/10 times replacing it cures the problem.
If your sure it isnt the problem, then there is another reason it is running lean.
K&N?(the oil is not compatable), Low Fuel pressure, vacuum leak

bayou39 · #15 (**permalink**) 04-30-2005, 07:44 AM

i have a tundra with the v8
is it the same checks?
thanks

Quote:

Originally Posted by mustang67408

Replace the MAF sensor. Make sure there isnt a piece of debris in it.
Here is a attachment to help you check the MAF SPECs. 9/10 times replacing it cures the problem.
If your sure it isnt the problem, then there is another reason it is running lean.
K&N?(the oil is not compatable), Low Fuel pressure, vacuum leak