CEL came on... P0101 & P0121

[jwalton]

Looking for any advice. On the way home from work tonight I had to accelerate to merge with traffic (honest officer, I was just merging at a <safe> speed) and the CEL lit up. I read the codes and P0101 and P0121 came up. I cleared them and drove a little further and they both came back.

First off, although I'm obviously still using the OEM MAF, I am using Tom's BTB. Could there be a link there somewhere? Has anyone else had this crop up? I've searched all over these forums as well as miata.net and I can't find even a single mention of both codes.

[Tom @ Fast Forward]

Jim,

Were you below or above 2000 RPM?

101 is the MAF signal out of expected range and 121 is the TPS out of expected range.

Just curious if you were high RPM at the time or low RPM? The PC-Pro tells the ECU that the TPS is at WOT as soon as it sees boost. I have not had either error code but wonder if there is a combination of WOT and MAF signal that it just doesn't like?

[jwalton]

When I first saw it I was on the freeway. Definately above 2000 rpm. When it came back on again I was cruising back across town and didn't see exactly when it came back on again. I reset it again last night and will drive it again tonight/tomorrow and watch for it.

[Kyp J]

I got both of those today along with a 171 (too lean) and I am currently running with the belt off and the bypass open. ( I was supposed to drop it off at the body shop but my new door didn't come in. I don't want it road tested with the belt on.)

My initial start up has been super low RPM and it usually chugs for about 30 seconds and finally jumps to 1500 and then evens out to 900 about. While chugging, it is getting about 15 or 16:1 A/F. I think that may be when my code came on but didn't really notice. I have been just driving around locally at under 50 mph

I got a code during last weekend's autocross, didn't read it and it went away. I don't know if any were saved from last Sunday or not. The CEL hadn't been on.

Maybe there is a date sensitve computer virus in the PC Pro.

[Tom @ Fast Forward]

Some of the code readers have a "snapshot" feature where they list the things that occured at the same time. That would be good to know as well.

Didn't I read somewhere about pulling the screen off the MAF for 171 codes?

[chuckerants]

Didn't I read somewhere about pulling the screen off the MAF for 171 codes?

That was Bill who mentioned it first. But that was for a MAF CEL that says it's getting too high a MAF voltage (?). Basically, the MAF is seeing too much air going through it.

After I removed the screen in my MAF, I never got the CEL again.

[pumpkin]

Can the MAF screen be removed in such a way that it can be replaced again.
Or is it torn up on removal?
JD

[Serpico]

I knocked mine out after I got the high voltage error code as well and the code never came back.

My screen came out in one piece and looks like it would go back in. Not sure if there is/was a tiny amount of glue holding it in place. I think it's just pressed in.

[chuckerants]

Can the MAF screen be removed in such a way that it can be replaced again.
Or is it torn up on removal?
JD

It popped out quite easily in one piece.

[jwalton]

Does the screen apply to the 101/121 codes as well, or only to the 171 code?

[jwalton]

Just went for a drive this morning and with normal driving the CEL didn't come back on. I even had a little fun with it (3rd gear, high rpm quick stab of the throttle to see where the boost was getting too, around 8lbs somewhere between 5-6krpm) and it still didn't come on. Then I came home. I pulled into the garage and with the car out of gear, went WOT which immediately brought the revs to about 6krpm and obviously got off the throttle. As the revs were naturaly coming back down, the CEL came on with the same two codes.

I also stopped by my mechanic friend and we looked up the wiring diagram and found that both the TPS and the MAF use the same ground (G119). We verified that the ground looked ok.

Thoughts?

[chuckerants]

After some research, it looks like the CEL I got was a P0103 - MAF circuit high input. Again, I never got that again after removing the MAF screen.

[jliu]

You may want to check around your EGR valve. I was getting a P0102 code a while back. It would only come on after I drove the car a bit. At first, I thought my intake/filter was loose. That was not the case. As it turned out, the harness of wires that comes out of the firewar was in contact with the EGR valve. The heat from the valve had melted the sheathing of the harness and a couple wires were exposed. That resulted in shorting out the wires. Reposition the egr valve a bit and re-taped the wires and all is well now. Hope that helps.

Jeff

[jwalton]

Thanks Jeff. I'll check that out. I've driven the car back and forth to work yesterday and today (about 180 miles total) including some brisk canyon driving this evening on the way home and no CEL. I'll do some more digging.

[Kyp J]

On the way back from Tom's after being there for the great Memorial Day Dyno experience, I used my blower a couple of times to pass some traffic up a hill (I can turn it on and off so I don't run the injectors out of stoich unnecessarily) and I got another pair of these codes (101, 121) reset them and didn't get any more.

[Tom @ Fast Forward]

Could be it didn't like being switched on while moving?

DTC P0101 MAF circuit range/performance problem
DETECTION CONDITION
• PCM compares actual input signal from MAF sensor with expected input signal from MAF sensor which
PCM calculates by engine speed.
• If mass intake-air flow amount is above 74.7 g/s {9.88 lb/min} for 5 s and engine speed is below 2,000
rpm with engine running, PCM determines that detected mass intake-air flow amount is too high.
• If mass intake-air flow amount is for below 5.3 g/s {0.70 lb/min} for 5 s and engine speed is above 500
rpm with engine running, PCM determines that detected mass intake-air flow amount is too low.
MONITORING CONDITION
—ECT is above 70 ｰC {158 ｰF}
— Throttle opening angle is above 50%
Diagnostic support note
• This is a continuous monitor (CCM).
• MIL illuminates if PCM detects the above malfunction condition in two consecutive drive cycles.
• PENDING CODE is available if PCM detects the above malfunction condition during first drive cycle.
• FREEZE FRAME DATA is available.
• DTC is stored in the PCM memory.
POSSIBLE
CAUSE
• MAF sensor malfunction
• Electrical corrosion in MAF RETURN circuit
• Voltage drops in GND circuit

DTC P0121 TP circuit range/performance problem
DETECTION CONDITION
• If PCM detects that throttle valve opening angle is below 12.5% for 5 s after following conditions are met,
PCM determines that TP is stuck close:
MONITORING CONDITION
— ECT is above 70ｰC {158ｰF}
— MAF sensor signal above 63.2 g/s {8.36 lb/min}
• If PCM detects that throttle valve opening angle is above 50% for 5 s after following conditions are met,
PCM determines that TP is stuck open:
MONITORING CONDITION
— Engine speed above 500 rpm
— MAF sensor signal below 5.3 g/s {0.7 lb/min}
Diagnostic support note
• This is a continuous monitor (CCM).
• MIL illuminates if PCM detects the above malfunction conditions in two consecutive drive cycles.
• PENDING CODE is available if PCM detects the above malfunction condition during first drive cycle.
• FREEZE FRAME DATA is available.
• DTC is stored in the PCM memory.
POSSIBLE
CAUSE
• TP sensor malfunction
• Electrical corrosion in TP signal circuit
• Voltage drops in reference voltage (Vref) supply circuit
• PCM malfunction

[Kyp J]

Quote: "Could be it didn't like being switched on while moving?"

I don't see how it would know that, but looking at the conditions in the code description, maybe going into boost (forcing TSP above 50%) and being at too low an RPM and/or being in too high a gear to get air flow moving soon enough (lugging the engine) sounds like a possible scenario. I don't always drive it like a small engined car when the SC is active. I just mash the gas and let the increased torque do the work. Maybe not the best idea. Its not really a big block V8. I will start down shifting before pouncing in the future.

[jwalton]

Could be it didn't like being switched on while moving?

Mine sounds pretty similar although, as you know, I can't turn mine on and off. I do find myself lower in the rev range due to the increase in torque. I also find that the light tends to come on after some full-throttle silliness.

[ThomS]

It popped out quite easily in one piece.

Chuck can you walk me thur where it is and how to remove it? The screen from the MAF for code P0171. I am getting that code now.
Tom just installed two new PC-PROs and after a tug of war between us and the car we finally won no more p1518.( KNOCK ON WOOD.) Thanks Tom customer service again is OUTSTANDING.---OUTSTANDING.... iDID HAVE P0101 AND P0121 THE OTHER DAY BUT THEY NEVER CAME BACK.

[ThomS]

That was Bill who mentioned it first. But that was for a MAF CEL that says it's getting too high a MAF voltage (?). Basically, the MAF is seeing too much air going through it.

After I removed the screen in my MAF, I never got the CEL again.

I have a question. Why would you take a screen out of the MAF when you think its getting too much air, when having the screen in would cut out some air flow? After I did this I am still getting this code P0171
signed puzzled.

[Serpico]

P-0171 is a lean condition code. Are you able to monitor your A/F ratio?

The code that is eliminated by removing the MAF screen is the P-0103.

[ThomS]

P-0171 is a lean condition code. Are you able to monitor your A/F ratio?

The code that is eliminated by removing the MAF screen is the P-0103.

No Iam not able to monitor the A/F wish I could
But if you read in this post they talk about P0171 and removing the screen
and no more code.?? But now that I look better you are right. darn.
What do I have to do to get rid of P0171??????????????????????????????
Thanks Serpico

[Serpico]

Without a way to measure your A/F ratio, it's hard to know just how lean your are and at what rpm/boost level you are seeing a lean condition.

You could try adding more fuel with your Powercard, PC -Pro or fifth injector if you have one. But again, it's hard to know how much to add without an A/F reading. However, I'd rather be too rich than too lean anyday.

You could also check for vacuum leaks as that may also be causing a lean condition.

Do your sparkplugs look OK?

[ThomS]

Without a way to measure your A/F ratio, it's hard to know just how lean your are and at what rpm/boost level you are seeing a lean condition.

You could try adding more fuel with your Powercard, PC -Pro or fifth injector if you have one. But again, it's hard to know how much to add without an A/F reading. However, I'd rather be too rich than too lean anyday.

You could also check for vacuum leaks as that may also be causing a lean condition.

Do your sparkplugs look OK?

Spark plug have only three thousand miles on them.
Tom just installed the PC-Pros and VAcuum test seem to be ok?

[ThomS]

If the car runs too lean for too long what will
happen ?

[Serpico]

Running very lean at WOT can only lead to bad things ( burnt pistons , valves ect ).

Safest thing to do is to get to a dyno to measure your A/F ratio and find out where you are lean ( low, mid or high rpms).

or invest in a wideband sensor/gauge so you can continually monitor your air/fuel. It cost me $275 , but I sleep much better these days.

Can you post both of your PC Pro's settings?

[ThomS]

No I dont know how to see them. Tom set them up and I do not know what they are.
Also I do not any one with a dyno here in this part of Ohio.
Don't make it easy do I ? Sorry. What is WOT? Sorry if that is a very dumb question.

[chuckerants]

According to my 99 Service Manual, P0171 is:

Fuel Injection closed loop correction and learning correction are above the specified value because of system too lean.

The diagnostic tree lists the following items as possible causes:


Fuel injector malfunction
Fuel pump malfunction
Fuel filter clogged
Fuel delivery hose clogged or leaking
and on and on


There's about twenty possible causes on this list.

The first thing I would do is to verify that you are in fact running a lean AFR.

[Serpico]

WOT = Wide Open Throttle

You really need to find out what your A/F ratio is ASAP and since there's no dyno in your area , I suggest that you buy a wideband setup.

Once you have a wideband gauge, it's really simple to adust the PC-Pros to get a nice steady air/fuel ratio.

[ThomS]

THANKS TO ALL. I guess I will just park the car. I am tired

[Kyp J]

I only got a 171 one time(recently) I think. Maybe also a long time ago when everything was going wrong. Anyway, I probably had some major vacuum and boost leakage even though my vacuum gauge usually shows about 18 inches at idle and boost about 13 lbs. I just found out the studs holding the intake manifold are breaking (they are replacements, not stock. I bought them from a generic fastener place and were probably not the right grade) and other nuts missing. Only one stud still holding at the top. I haven't checked underneath yet. Waiting on all new studs and nuts.

Anyway, it may not hurt to verify that the manifold nuts are still all tight. I may have brought this on myself during the rebuild when the studs got pulled out due to locktite on the nuts during the original SC installation.

Kyp

[ThomS]

I AM JUST WONDERING? If the Maf is seeing too much air go through it and you take out the screen won't the MAF see even more air go through it? I have P0101 which is if I am correct MAf code. Can you explain for me. Thanks in advance?
ThomS

That was Bill who mentioned it first. But that was for a MAF CEL that says it's getting too high a MAF voltage (?). Basically, the MAF is seeing too much air going through it.

After I removed the screen in my MAF, I never got the CEL again.

[Kyp J]

Thom

From page 2, the write up from a manual that Tom posted says a P0101 can be caused by too much air or too little air depending on some conditions. Mostly, I think the PC Pro jamming on the throttle position sensor is what is causing the code based on how you drive the car. Just don't go into boost below 2000 RPM and it shouldn't see all the conditions needed to set the code.

Also, you might try wiring open the bypass for a while to see if you still get any codes. This should prevent any positive pressure under normal driving, preventing the PC Pro from activating. However, I was seeing a bit of positive on my vacuum/boost gauge in high RPM windups when I was driving with my "valet" mod. It was obvious because the wideband went richer. I don't know if it over came the bypass or my "valet" mod started closing it due to extended low vacuum. OK that was too much information.

[Supermiataman]

I AM JUST WONDERING? If the Maf is seeing too much air go through it and you take out the screen won't the MAF see even more air go through it? I have P0101 which is if I am correct MAf code. Can you explain for me. Thanks in advance?
ThomS

i might be thinking off, but I'd see it doing the opposite.

MAF has less area (w/ screen) for the air to go through, so removing the screen will slightly enlargen the hole (by getting rid of the grid) and so if the same amount of air is going through it, it might think less is (slightly less, due to the decreased restriction.)

Hope that makes sense, in my head it does, but I typically underexplain things. and then i've been completely wrong before too...but nonetheless, that's my take- less restriction.

[Tom @ Fast Forward]

As the engine/blower sets how much air is flowing, the screen should have no effect on the "amount" of air. However, it will have an effect on the velocity of the air. That could have an effect on the MAF? Not sure why it would. I can't help much. The screen on my 99 has been off since the days on my original hotside. The screen on my 05 is still there. Neither of them throw codes.

[jwalton]

As the engine/blower sets how much air is flowing, the screen should have no effect on the "amount" of air. However, it will have an effect on the velocity of the air. That could have an effect on the MAF? Not sure why it would. I can't help much. The screen on my 99 has been off since the days on my original hotside. The screen on my 05 is still there. Neither of them throw codes.

It would really depend on how close the sensor element is to the screen. If it was immediately behind the screen, it would either be in the wake of one of the screen elements or in the higher local flow coming through the elements of the screen (or worse, stradling both). Yes, in the immediate vicinity of the screen (like within a downstream thickness of the screen or two, it would be flowing faster, but very, very quickly after that the flow will be back down to what it would be as if the screen weren't there at all. I think our sensor element is well outside this region.

The one benefit of the screen is that it acts as a flow straightener which will aid in accurate measurements of the amount of air actually going through the pipe. Wind tunnels use screens in front of the test sections to smooth and even out the flow in exactly the same way.

Mine hasn't thrown the code that started this whole thread in almost 2 months and I still have my screen in. I think that it has a lot to do with the <2k rpm and boosting conditions that Kyp J brought up.

[ThomS]

Well I am going to revive this post. I have been diving my car all summer now since I got it fixed and it has been fine. All of a sudden Iget a code P0507 my mechanic say he knows what that is and Mazda has told him how to fix it, It has nothing to do with a SC supposedly. ANy way it happens enought that mazda knows about it but not enough that they have sent out a bulletin. One way or one part of fixing it is to reset the system, now that car has to learn how to be driven again. OK next I get
P0506 twice, just reset it never comes back, guess it happened because of the system being reset. then I get P0121, not sure why, reset it it goes away, they say it is from the system being reset again.OK. 300 miles later it comes back. Reset it again. 65 miles later I get it back P01212 and P0101, reset it again, still not sure why car ids running great.
85 miles later P0101 P0121 P0171, car is stiull running real fine.
COdes are going to be the death of me. Any idease why? I need to know this.
Thom

[jwalton]

I ended up going through this a bunch with a whole lot of code clearing and it finally just stopped happening. Not sure why. Maybe subconciously I'm not going WOT at low RPM's. Again, not sure. If I were you, I would try and find out by experimenting with driving habits to see if you can make it throw the code at will. If you can do that, then you can start to narrow down the possibilities.

I might have mentioned this during one of my earlier posts, but I experimented with going full throttle up to redline just sitting in the driveway and then getting completely off the throttle and let the ECU bring the car back down to idle. I got it to throw the codes that I started this thread with pretty reliably at the time. A place to start...

[ThomS]

I am pretty sure it showed these code without going to boost or WOT at 2000 rpm. I was pretty much at 3000 or more when I did go into boost last night. I need to watch better what is happening when it happens than I do now. I have been all over the scale on how I have been driving that car and codes still show up. NOw I am afraid to drive the car with P0171. Thanks for your post.

[Kyp J]

I wrote a big long explanation but deleted it.

This may not be the cause but with so many codes it might be wiring or grounds. If you notice, there are really a lot of gnd wires around the engine. This must be to prevent noise on the sensor wires which this sounds like if it was in an old fashioned computer. (New fashioned computers are built into box the size of a small coin and don't have ground wires.)

[Snakeoil]

COdes are going to be the death of me. Any idease why? I need to know this.
Thom

Thom,

If you remember correctly Joe Btfsplk had a black cloud follow him wherever he went. Man had perpetual bad luck. You might consider changing that picture you use and going to something a little more benign like Freddy Kruger or Casper the Friendly Ghost. All your codes might suddenly disappear.
Just a thought.
Rob

[ThomS]

Thanks Rob, LOL I think you might be right.
Right now Kenjitsu Auto has my car and between them and Tom I think
they might have the problem fixed, but time will tell..
If not then I will for sure think about what you have said because you might be right.. But Tom gave me that call sign, and it will be hard to change that..
Thanks Tom

Thom

[Tom @ Fast Forward]

Maybe if we rotate that picture so it is upside down, it might be better.