P0101 MAF Circuit “A” Limp Mode

[white_lx]

I agree with Jerry that the bypass wiring is not up to Toyota standards. Especially the strain relief on the wires coming out of the potted module seem a weak point. You could try a wiggle test. If CEL is not easily set, then it is probably best to wait for FF data.

If FF shows that the MAF signal is suspect, my next approach would be to jumper most of the MAF wires, as the Hewitt module really only changes the 'THA' signal wire. All other 4 wires could be just bypassed (you can check that with a multimeter).

One other possible cause related to the same bypass module: Is your starter relay output wired into the module? This is the single wire on the spade connector into the module. It will activate the module for a few seconds when the starter is triggered. It could have a sensitive input and trigger as a result of noise/stray voltage. You could unplug the space connector at the module and test that as well. Make sure to cap off the wiring running back into the fuse box, so it doesn't get shorted. Only downside it that you would need to start immediately after turning the key (as per instructions).

 

[rxaaron]

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

version 1

View attachment 3428059

My kit looks like this:

 

[jerryb]

Honestly.
I'd cut the wires and solder it. But I realize that's not an option all the time.

Usually if you took those apart you'd see some- different countries manufacturing techniques- and wonder why.

But, what white LX said is good.
You're better off unplugging all that and putting it back to stock in 3 minutes and driving and see if maf codes go away.

 

[rxaaron]

I agree with Jerry that the bypass wiring is not up to Toyota standards. Especially the strain relief on the wires coming out of the potted module seem a weak point. You could try a wiggle test. If CEL is not easily set, then it is probably best to wait for FF data.

If FF shows that the MAF signal is suspect, my next approach would be to jumper most of the MAF wires, as the Hewitt module really only changes the 'THA' signal wire. All other 4 wires could be just bypassed (you can check that with a multimeter).

One other possible cause related to the same bypass module: Is your starter relay output wired into the module? This is the single wire on the spade connector into the module. It will activate the module for a few seconds when the starter is triggered. It could have a sensitive input and trigger as a result of noise/stray voltage. You could unplug the space connector at the module and test that as well. Make sure to cap off the wiring running back into the fuse box, so it doesn't get shorted. Only downside it that you would need to start immediately after turning the key (as per instructions).

Pictured is where the spade connector is tied into the starter relay. I don't really understand what you mean by jumping the MAF wires. Reading the service manual, does the engine have to be under a "load" condition for P0101 to trigger? That may make it difficult to trigger by wiggling the wires from under the hood.

I guess the current plan is wait and see if I can get that freeze frame data.

 

[rxaaron]

Honestly.
I'd cut the wires and solder it. But I realize that's not an option all the time.

Usually if you took those apart you'd see some- different countries manufacturing techniques- and wonder why.

But, what white LX said is good.
You're better off unplugging all that and putting it back to stock in 3 minutes and driving and see if maf codes go away.

What wires are you referring to? The problem with removing the kit is it has the block off plates installed which aren't the easiest to get to. Likely there's an underlying problem with the SAIS system which is the reason the previous owner installed the bypass. Removing everything would just throw another CEL code if is the case. I will remove the system as a last resort though to rule it out if I can't find a fix elsewhere.

 

[jerryb]

I mean it only as a check to see if maf codes go away, then you'd know.
It's not horrible to driving it with the plates in.
The valves will just just think they're stuck closed. Safe mode or not, I'm not sure.

 

[bgibson23]

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!

I have a 2007 5.7 Tundra and I am having similar issues. I keep getting P0101 even with a new MAF sensor. Sometimes I would get "system too rich". During hot/humid days, my truck will surge/die while driving it. Starts right back up. I've taken to a shop but they were not able to reproduce the problem. Sometimes when the surging happens, I get a code, sometimes I don't. This only happens randomly which is kinda scary, especially while pulling a camper . I also have the Gen 1 Hewitt kit. I'm beginning to wonder if something with it has failed.

I have screenshots of my freeze frame data that I'll add up here if it may help figure this out. I honestly think we may be having the same issue. You're one of the first that I have seen having a similar issue that I've dealt with for the last 4 summers.

 

[2001LC]

If you came to me:
1) Since you mention; "may have correlation here with wet or humid conditions". I'd be looking at windshield and its molding, if replaced. Water entry down "A" pillar, may get to cabin wiring. This includes junction box LH & RH and CPU's like ECM. I'd look for any signs of current water leakage or past.
2) I'd make sure no obstruction in air intake. Such as a nest inside the fender wells air intake tube. Also, that fender skirt in place.
3) I'd study service history at Lexus, Toyota and carfax. Looking for history of engine DTC or any engine work done.
4) I'd inspect the S.A.I.S filter, with inspection camera. This would give me a very good idea if Hewitt kit installed in response to and issue or preemptively. If filter is gone, this indicates kit installed in response to S.A.I issue. I'd then, do a compression test. I'd also inspect to see if o2's are stock setup or have extenders on them.
5) I'd recommend removing all none factory wire/devices. Taking the vehicle back to stock. With one exception; I'd put a replaceable filter on the S.A.I pump. Which if filter is gone. It may require #1 switch and possible the #2 switches be replaced also.

We go down a rabbit hole with most any none Toyota part installed. I've seen issue chased for years even decades, by shop after shop. That by just changing a non Toyota component back to OEM, corrects.

S.A.I replaceable filter mod:

S.A.I. Filter Modification, in VVT engines. To prevent its failure! Alert Alert!

We've a $2.00 part in the S.A.I. (secondary air injection) system of the VVT engine, that is taking-out ~$7,000.00 $15,000 $25,000 (inflation) in parts. WOW! I've a very easy and cheap WORK AROUND. You are going to love this ;) This thread is dedicated to the 4.7L 2UZ-fe VVT engine, in the...

forum.ih8mud.com

FWIW. I may do a 200 series 5.7L S.A.I.S filter mod within the next year, since I've a request to do one. They have two S.A.I.S. pumps ( blowers) inside RH fender well. They should be much less labor intensive to put on replaceable filters. The tricky part will be to make apparent and easy to replace filter, as I did on the 100 series 4.7L.

 

[white_lx]

I have a 2007 5.7 Tundra and I am having similar issues. I keep getting P0101 even with a new MAF sensor. Sometimes I would get "system too rich". During hot/humid days, my truck will surge/die while driving it. Starts right back up. I've taken to a shop but they were not able to reproduce the problem. Sometimes when the surging happens, I get a code, sometimes I don't. This only happens randomly which is kinda scary, especially while pulling a camper . I also have the Gen 1 Hewitt kit. I'm beginning to wonder if something with it has failed.

I have screenshots of my freeze frame data that I'll add up here if it may help figure this out. I honestly think we may be having the same issue. You're one of the first that I have seen having a similar issue that I've dealt with for the last 4 summers.

Your mass flow rate of 8.9 lbm/min (67 g/s) is very high for 1500 rpm, even with a 5.7. But not implausible at ~85% engine load. Was this while pulling uphill or flooring it (throttle position is only ~30% according to the data). If not, then the mass flow rate is certainly suspect. (You can use VE Calculator - https://atgtraining.com/atg-volumetric-efficiency-calculator/ to test out some numbers.)

Does this FF data have multiple frames? I'd like to see the MAF data just before and after setting of the code, to see if the MAF signal is stable.

The intake air temperature of 107F seems fine (comparible to the outside temperature that day?). Same with coolant temperature. Those signals also run through the Hewitt module.

However, your long term fuel trims are quite high (negative) on both banks (-15%, -16%). So, this could indicate another underlying problem. Are they always that high, even when the engine is running fine?

 

[white_lx]

Pictured is where the spade connector is tied into the starter relay. I don't really understand what you mean by jumping the MAF wires. Reading the service manual, does the engine have to be under a "load" condition for P0101 to trigger? That may make it difficult to trigger by wiggling the wires from under the hood. I guess the current plan is wait and see if I can get that freeze frame data.

The code is set if the calculated load from the MAF-based air amount does not match the calculated load from the injected FUEL amount (they should be related at the lambda value * 14.7). If the MAF load is outside 40%-200% of the FUEL based load, the code is set. It does not mean that the engine has to be under load, but it is more likely.

If you wiggle the wires and just look at the MAF value, then you may be able to find the location of the problem. No need to load up the engine.

The bypass modules work as follows: the MAF air flow and ground/power are fed through uninterrupted. But there is an extra female/male connector in between the circuit after installing the module. That's why it was suggested to just bypass the extra connectors and solder the wires. At a minimum I would spray some Deoxit on those connectors as the plating may be different from OEM standards. Especially since humidity/heat seems to make the symptoms worse. Note that the module is powered from +12V and GND signal on the MAF connector, so even after soldering those wires will need to remain spliced.

The engine coolant temperature sensor and the air intake temperature sensor are fed through the little module and are switched so the ECM is tricked into thinking that the outside air temperature is below freezing and the air injection cycle will not run. After a few seconds the temperature sensors are switched back and the engine runs normally. At that point the ECM will no longer try to run the air injection cycle.

 

[rxaaron]

I thought I had this problem behind me after replacing a post-cat O2 sensor and not having any issues for months. DTC code back this morning. I no longer think there's any correlation with moisture or humidity- the cabin/under dash area is bone dry.

See the freeze frame data for those interested:

 

[rxaaron]

 

[rxaaron]