Check Engine Light - Code diagnosis help request

[spaldam]

2000 Tacoma with SR5 badgeing (though I'm not certain it's really an SR5 as it has manual windows and door locks, and aftermarket CC). Build date is Aug 2000.

I pick it up pretty cheap, but it has been a big project for the last year and has had a lot of stuff replaced, including the engine (original engine had a bad cylinder and was overheating) and a complete tuneup.

I recently had a California spec Magnaflow Cat put on it and was hoping this would be the last thing needed to get the check engine light to turn off. Strange thing is that every exhaust shop I talked to said the 2000 Tacoma has 2 cats, but I only found a spot for one, so I'm not sure if someone really messed with this truck before I bought it or what...

After getting the new cat installed I un-plugged the battery for a while. The first time I starting the truck up after that it ran rough, and seemed to stall slightly when trying to accelerate. Once it was allowed to warm up completely the check engine light came back on and the truck started to run smoothly will plenty of power.

Anyway here's the codes I'm getting now:

P0125 - Insufficient coolant temperature for closed loop fuel control.
Thermostat is about 9 months old.
Coolant appears to be filled to the top.
The temperature gauge appears to be functioning normally.
The cooling fan clutch was welded because (according to the shop that did the tuneup) it wasn't getting enough air flow to turn it engage the fan clutch.

P0171 - Air/Fuel mixture system lean bank 1 (Cylinder number 1 denotes bank 1)
The engine run fine once the check engine light is on, so I think I've got enough fuel.
The MAF sensor was replaced as part of the tune up.
I don't hear a misfire other then it was running rough at first.
I'm not sure what condition the O2 sensors are in, or if maybe I'm missing one (along with another cat). Does anyone know what the acceptable Ohm parameters are?
I guess I should check for vacuum leaks as well.

Thanks in advance for any ideas or suggests.

 

[spaldam]

After reading some documentation on the P0125 code, it seems it has nothing to do with the cooling system, but is actually related to the O2 sensor. I guess I should be looking at replacing the "heated oxygen sensor (bank 1 sensor 1) circuit".

Can anyone confirm this?

 

[raydouble]

After reading some documentation on the P0125 code, it seems it has nothing to do with the cooling system, but is actually related to the O2 sensor. I guess I should be looking at replacing the "heated oxygen sensor (bank 1 sensor 1) circuit".

Can anyone confirm this?

I've looked into this a bit and never really gotten a good answer.
But it appears to only have to do with the oxygen sensor not the cooling system.

Here is a couple good resources/posts from Dick Foster on TTORA about testing.

TTORA - Oxygen Sensor Test - Faq

Front oxygen sensor replacement - TTORA Forum

 

[spaldam]

Thanks for the reply. This is very helpful. I'm going to check out the front O2 sensor and possibly replace it. I'll let you know how it goes.

 

[spaldam]

I use my MAF cleaner to clean the MAF and the Throttle body, and shot some down the port to the IAC valve.

I also replaced the front (upstream) O2 sensor.

The P0125 code is gone, but the P0171 is still present (I pulled the EFI fuse to clear the CEL and drove it twice before it came back on).

I guess I'm going to start searching for vacuum leaks.

I have an extra throttle body with all the sensors attached (original one with 180K miles). Maybe I should put it on and take off the one that came with the Engine from a 4runner (100K miles - unknown year)?

 

[raydouble]

Is the PCV valve original? Could be real cheap fix.

OBDII P code lists + probable causes 5VZ 3.4L

Look on page two for some other ideas......

 

[TheDurk]

I've looked into this a bit and never really gotten a good answer.
But it appears to only have to do with the oxygen sensor not the cooling system.

Here is a couple good resources/posts from Dick Foster on TTORA about testing.

TTORA - Oxygen Sensor Test - Faq

Front oxygen sensor replacement - TTORA Forum

Ray, the stuff in the first link about testing the sensor function won't work for '99-'00 Cali. or '01+ front A/F sensors. The heater part is fine.

The second link is so full of misinformation and BS that if you don't already know this stuff, you are better off never reading it. Sorry, but I think it will confuse people more than it helps. (I know I'm a rookie here, but I'm a vet at YT and T4R.)

 

[4LLC]

you need a new maf sensor to clear up your 171 code

 

[raydouble]

Ray, the stuff in the first link about testing the sensor function won't work for '99-'00 Cali. or '01+ front A/F sensors. The heater part is fine.

The second link is so full of misinformation and BS that if you don't already know this stuff, you are better off never reading it. Sorry, but I think it will confuse people more than it helps. (I know I'm a rookie here, but I'm a vet at YT and T4R.)

The propane test doesn't work for the a/f sensors or the values are wrong?

No worries, I could use the help.
I'm spreading myself thin here.

 

[TheDurk]

The propane test doesn't work for the a/f sensors or the values are wrong?

No worries, I could use the help.
I'm spreading myself thin here.

Unlike the classic O2's, the A/F's do not produce voltage. The ECU applies a steady 3.3V and measures the current through the sensor. At the stoichimetric point, current flow is zero. The voltage needs to be supplied by the detection circuit. So I don't think you would ever get a reading just hitching one to a voltmeter. I'm not willing to put a $100 sensor at risk to find out.

Here is a good explanation of the difference:http://www.autoshop101.com/forms/h37.pdf

 

[raydouble]

Unlike the classic O2's, the A/F's do not produce voltage. The ECU applies a steady 3.3V and measures the current through the sensor. At the stoichimetric point, current flow is zero. The voltage needs to be supplied by the detection circuit. So I don't think you would ever get a reading just hitching one to a voltmeter. I'm not willing to put a $100 sensor at risk to find out.

Here is a good explanation of the difference:http://www.autoshop101.com/forms/h37.pdf

Nice, I'll have to peruse later.

 

[spaldam]

TheDurk: I guess these "Federal Emissions" 2000 Tacoma's are somewhat rare, because just about everyone I've talked to says I should have 2 cats and an A/F sensor, but I only have one cat and a O2 sensor. Also the sticker under the hood specifically says it's not intended for sale in Calofornia.

The P0171 is still a problem, but I got some help with that, and so far we've found a cracked hose. That helped but didn't fix it completely. We are looking into fuel system and injector problems next.

4LLC: The MAF sensor was cleaned and it made no difference. It's been tested and appears to be working fine. Plus it's only 9 months old anyway.

raydouble: PCV valve only allows air to blow threw one way... out of the Crank Case.

 

[TheDurk]

TheDurk: I guess these "Federal Emissions" 2000 Tacoma's are somewhat rare, because just about everyone I've talked to says I should have 2 cats and an A/F sensor, but I only have one cat and a O2 sensor. Also the sticker under the hood specifically says it's not intended for sale in Calofornia.

They probably were, because even in '99 Toyota was selling 'Cali'. rigs all over the country. (I got my '99 Cali. 4Runner in NJ). But URD has listings for both, and shows the Denso part numbers. They definitely exist. Linky: Oxygen / AFR Sensors - Underdog Racing Development Toyota went to 50-state two-cats only in 2001.

 

[spaldam]

Since I was running out of time I some help, and finally got it to pass inspection yesterday. The engine was defiantly running lean with a crack in one hose, and a clogged up fuel system. The fuel filter was black with dirt when poring out it's contents. Sine the intake had to be pulled apart to get to the injectors, the original intake from the original engine was used as we figured it would potentially be a better fit for the rare Fed Emissions ECU (not sure if theres really a difference or not). The guy that was helping me out riged up a harness to the injectors to activate them and stayed cleaner threw them for about 20 minutes (it was either that or sent them out for a wee). We also found a ground that wasn't attached to the engine; probably missed from the engine swap.

All this, and every thing else that was wong with it when I first picked it up, makes me think this truck was submerged or in a flood or something like that. Any way, hopefully it's now to a point were it will last another 10 years with regular maintenance.

The next big project is going to be refurbishing the torn up and oderous interior.