P0101 MAF Circuit “A” Limp Mode

[rxaaron]

I’m hoping for some assistance with a reoccurring issue with my 07 LX470.

I bought the truck from an individual this May. Ever since I’ve been having sporadic problems with a dtc code, P0101, “mass or volume air flow sensor ‘A’ circuit range/performance.” This only happens about every 500 miles or so. The check engine light comes on with some of the traction disabled lights and the truck goes into a limp mode with reduced power and increased fuel use. I can clear the code with a scan tool and the truck is fine for another ~500 miles. There may be some correlation here with wet or humid conditions. The truck also has one of the SAIS bypass plug and play kits from Hewitt Technologies installed by previous owner(s).

So far I’ve replaced the MAF sensor with new oem unit, pcv valve , and cleaned the throttle body. I took it to an independent shop, who was unable to find any issues.

I contacted Hewitt Technologies for help. A tech there recommended fuel injector cleaner, and upstream o2 sensors in addition to what I’d already done.

Any advice for next steps? Should I be running high octane fuel or does that matter? I know Lexus “requires” it.
Thanks in advance!

 

[Malleus]

What's the value of the bypass kit? To you, I mean.

 

[rxaaron]

What's the value of the bypass kit? To you, I mean.

What do you mean?

 

[Malleus]

From the FSM:

 

[Malleus]

 

[Malleus]

 

[Malleus]

The above assumes there is only the P0101 code present. If there are others, they have to be resolved prior to resolving the P0101.

Of course, Toyota didn't plan for someone to install a SAIS bypass, so that's not going to be covered in the FSM...

 

[Malleus]

What do you mean?

I mean, what does it do for you? Has the SAIS system been removed? Is it necesssary for your operation/daily use?

 

[Malleus]

Do you have a copy of the FSM?

 

[rxaaron]

I mean, what does it do for you? Has the SAIS system been removed? Is it necesssary for your operation/daily use?

I don’t know the full vehicle history. It’s possible part of the SAIS failed and that is why the bypass kit was installed.

 

[rxaaron]

Do you have a copy of the FSM?

Factory service manual? I have access to what’s posted on charm.li and have tech stream on a laptop.

 

[Malleus]

Factory service manual? I have access to what’s posted on charm.li and have tech stream on a laptop.

There is a copy of the 2006 LX470 Factory Service Manual (FSM), in the Resources section.

These manuals are very large, and it takes some time to edit and compress them so that they are usable from a forum download. If it would be of use to you, I can put a copy of the 2007 LX470 manual there for you (and anyone else who has a 2007 LX470). In the meantime, the 2006 FSM will get you by on most problems.

The information I posted above was from the 2007 FSM.

 

[Malleus]

I don’t know the full vehicle history. It’s possible part of the SAIS failed and that is why the bypass kit was installed.

I'd consider removing it. But that's just me. At $450 new, someone might want it, for a deal.

 

[rxaaron]

I'd consider removing it. But that's just me. At $450 new, someone might want it, for a deal.

My truck has the gen 1 kit that’s only $150. It has the block plates installed I’m pretty sure and I don’t know right off how to take those out.

 

[rxaaron]

I'm going to replace the pre-cat air/fuel sensors next week and dump some injector cleaner in the gas.

 

[white_lx]

I'm going to replace the pre-cat air/fuel sensors next week and dump some injector cleaner in the gas.

If you have access to Techstream, I would test the a/f sensors before replacing them using the a/f fuel trim active test. You can use the secondary oxygen sensors to confirm the readings.

Also check the MAF connector. Some people here have posted MAF sensor related problems were solved by replacing the connector..

 

[rxaaron]

If you have access to Techstream, I would test the a/f sensors before replacing them using the a/f fuel trim active test. You can use the secondary oxygen sensors to confirm the readings.

Also check the MAF connector. Some people here have posted MAF sensor related problems were solved by replacing the connector..

I did the test this morning based on your tutorial from another thread. How do you confirm with secodary o2 sensor data? The a/f sensors seem good from my understanding so far:
Lamda 0.883,0.883 when running +12.5%, 1.116,1.127 when running -12.5%. Those numbers were very similar to yours after you swapped to a new sensor.

 

[white_lx]

If you drive the fuel control rich (+12.5%), you should see the secondary oxygen sensors follow after a few seconds, i.e. > 0.45V. And when driving it lean (-12.5%), the secondary oxygen sensors should follow at <0.45V. Flip the lean/rich conditions back a forth a few times and check that the secondary oxygen sensors keep following. This will confirm that your primary oxygen sensors are not 'lying'. Alternatively, you can check the tailpipe emissions, but that requires a lot more equipment.

(btw: The fuel control active test also has another feature. When none of the three buttons are 'lit' the engine is in closed loop fuel control. Then press the 0% button (it lights up blue) to put the engine in open loop. The difference between these two situations, will tell you how much the A/F sensors have to step in, v.s. open loop control with the MAF and known injector volumes. You can flip back and forth between open and closed loop by pressing the 0% button.)

Any chance there is freeze-frame data from when the code is set? How are the fuel trims? It almost seems like you are temporary loosing the MAF signal when the code is set, since it doesn't come right back. The MAF would have to be seriously off at that moment as the code is only set when MAF calculated load is less than 40% or more than 220% of the expected value. (this is a 'rationality' code) Any chance there is something loose in the air intake (leaf, debris)?

If the Hewitt bypass plates are indeed installed, we can ignore the 'SAIS vacuum leak'. Any other possible intermittent vacuum leaks?

 

[rxaaron]

If you drive the fuel control rich (+12.5%), you should see the secondary oxygen sensors follow after a few seconds, i.e. > 0.45V. And when driving it lean (-12.5%), the secondary oxygen sensors should follow at <0.45V. Flip the lean/rich conditions back a forth a few times and check that the secondary oxygen sensors keep following. This will confirm that your primary oxygen sensors are not 'lying'. Alternatively, you can check the tailpipe emissions, but that requires a lot more equipment.

(btw: The fuel control active test also has another feature. When none of the three buttons are 'lit' the engine is in closed loop fuel control. Then press the 0% button (it lights up blue) to put the engine in open loop. The difference between these two situations, will tell you how much the A/F sensors have to step in, v.s. open loop control with the MAF and known injector volumes. You can flip back and forth between open and closed loop by pressing the 0% button.)

Any chance there is freeze-frame data from when the code is set? How are the fuel trims? It almost seems like you are temporary loosing the MAF signal when the code is set, since it doesn't come right back. The MAF would have to be seriously off at that moment as the code is only set when MAF calculated load is less than 40% or more than 220% of the expected value. (this is a 'rationality' code) Any chance there is something loose in the air intake (leaf, debris)?

If the Hewitt bypass plates are indeed installed, we can ignore the 'SAIS vacuum leak'. Any other possible intermittent vacuum leaks?

Yes the O2 sensors confirmed the A/F in this case then. I'm fairly certain theres nothing in the air intake as I've had most of that apart since having this problem (new filter, MAF, and cleaned throttle body). I don't have any freeze frame data. I'll have to wait for the CEL to come back on and look into that next time.

I'm not aware of any vacuum leaks. I haven't officially done a vacuum leak test. I had the truck at an independent shop for diag, and they dismissed the idea of vacuum leaks as well with the theory the engine would be having issues running all the time with a vacuum leak. They suggested to leave the Hewitt bypass kit unplugged, but this will continue to trigger CEL since the SAIS plates are installed forcing the system closed.

I looked at the connections on the MAF and there's no visually damaged wiring.

I really appreciate your help on this. I'm running out of ideas.

 

[jerryb]

I'd check the wiring first. PLug and play version $$ - I'd be suspect.
PLug and play $$$$ version - I'd blame the air control driver.

Post a pic of what you have, look for a little black potted square box mounted on the pass fender maybe, close to the air box with colored wires coming out.
OR over by the brake booster on the driver's fender wall rectangle box, bigger connector with a big(thick) battery voltage wire in it, blue/yellow, maybe red.

OR sell me your 100 for cheap

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