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Discussion Starter · #1 ·
I put on the K&N CAI about 500 miles/2 weeks ago, but now I have a problem. I will be driving down the road, and the car will go into limp mode. When I read the code, it comes back "P0068 MAF/MAP Sensor Throttle Position Correlation", but if I look at the DTC list here it comes back "P0068 Throttle Body Airflow Performance ECM". I am wondering if the description from the handheld code reader is just a more generic description, not specific to our engines/PCM's.

So here is what I have done, I have taken out my MAF sensor and cleaned it out with throttle cleaner. There was a light coating of oil on it, I assume from the K&N Cone. It seemed to have fixed the problem for a couple days, but now it is back. Also it has nothing to do with how hard I am driving the car. Most of the time it happenes in the 40-60 mph while I am cruising.

What are your guys thoughts about this? I am thinking about taking off the intake pipes and giving them a good spraying. Am I barking up the wrong tree?
 

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ptparker said:
I put on the K&N CAI about 500 miles/2 weeks ago, but now I have a problem. I will be driving down the road, and the car will go into limp mode. When I read the code, it comes back "P0068 MAF/MAP Sensor Throttle Position Correlation", but if I look at the DTC list here it comes back "P0068 Throttle Body Airflow Performance ECM". I am wondering if the description from the handheld code reader is just a more generic description, not specific to our engines/PCM's.

So here is what I have done, I have taken out my MAF sensor and cleaned it out with throttle cleaner. There was a light coating of oil on it, I assume from the K&N Cone. It seemed to have fixed the problem for a couple days, but now it is back. Also it has nothing to do with how hard I am driving the car. Most of the time it happenes in the 40-60 mph while I am cruising.

What are your guys thoughts about this? I am thinking about taking off the intake pipes and giving them a good spraying. Am I barking up the wrong tree?
yep the handheld scanners are just the general code. The redline DTC is the one to go off.
 

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ptparker said:
I put on the K&N CAI about 500 miles/2 weeks ago, but now I have a problem. I will be driving down the road, and the car will go into limp mode. When I read the code, it comes back "P0068 MAF/MAP Sensor Throttle Position Correlation", but if I look at the DTC list here it comes back "P0068 Throttle Body Airflow Performance ECM". I am wondering if the description from the handheld code reader is just a more generic description, not specific to our engines/PCM's.

So here is what I have done, I have taken out my MAF sensor and cleaned it out with throttle cleaner. There was a light coating of oil on it, I assume from the K&N Cone. It seemed to have fixed the problem for a couple days, but now it is back. Also it has nothing to do with how hard I am driving the car. Most of the time it happenes in the 40-60 mph while I am cruising.

What are your guys thoughts about this? I am thinking about taking off the intake pipes and giving them a good spraying. Am I barking up the wrong tree?
Actually these DTC descriptions are just different ways of stating the same thing.This DTC is unfortunately very common when using a CAI (especially one that is ACTUALLY WORKING!) Here are the basic enable criteria for a P0068 from the FSM
The powertrain control module (PCM) uses the following information to calculate an expected airflow rate:

• The throttle position (TP)

• The barometric pressure (BARO)

• The super charger inlet pressure (SCIP)

• The intake air temperature (IAT)

• The mass air flow (MAF)

• The engine RPM

If the PCM detects the airflow rate is more than expected, DTC P0068 sets.
Basically the MAF is saying it's seeing more airflow than what the ECM is expecting based on conditions and values from other sensors. Unfortunately I dont know what you are going to be able to do about this, other than using your code reader to clear just the DTC when it sets. In a perfect world you would go into the ECM table where the outside "tolerance %" for this DTC was stored and make it larger- fixed. Too bad nobody has hacked this box...YET!

It stiill could be a bad MAF (since few others have commented on this DTC) but you might have trouble getting your dealer to look at it unless you swapped all of you facory intake back in first. Maybe you have a buddy you can swap MAFs with to diagnose??

ALSO- dont use carb cleaner on a MAF as it can damage it if it is the corrosive solvent type (like GM Cleens) Use only the type with high alcohol content that evaporates immediately when you spray it on your hand.(freezing it off in the process - lol)
I actually use GM BrakeCleen for MAF cleaning, never had a problem
WOT
 

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Ahhh... so there we go.. any idea what that parameter looks like ***? You would think that it's pretty small if just a CAI is setting it off...
 

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Hey ***, Not to second guess at all. :) But from your post, you seem to suggest that it's a lookup table ("expected value") check. Are you sure that's the case? The code description "P0068 MAF/MAP Sensor Throttle Position Correlation" seems to suggest that it's more of a MAF/MAP/Throttle rationality check, in which case you would think that the ECM would be able to cope with it just fine w/o failing (as long as none of the sensors were out of range). I'm just wondering if maybe he has a leak/obstruction somewhere, or if the airflow through the MAF is unusual or something. Not ready to give up just yet, cause lots of ppl use intakes w/o problems! :)
 

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Mine has been off for 3 weeks, I think, at this point. The temps have been from 93-58 in the last two weeks too. I'm not sure that it's solved, but it sure seems to have gone away. Perhaps the ECU needs time to adjust??? How long does an ECU take to adjust to something like that? Is it nearly instant, or does it slowly rebuild the tables to match?
 

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Well that's the thing - the ECM doesn't "adjust" to airflow numbers as far as I understand (not as in updating its tables). It will have some sort of rationality check that compares MAP to MAF to temp to TPS to whatever to make sure that all the values "agree" with one another. Ie if you read huge MAF and TPS=WOT, but MAP says high vacuum, something is wrong, and you fail the rationality check.

The thing is, because it's a rationality check, as long as everything is working properly, it SHOULD be able to cope with more airflow (as long as the other parameters, like MAP, agree with it). That's the reason I wonder if maybe he's got a vac leak or something somewhere. Otherwise, if it can't cope with relatively minor changes in air flow, you'd set codes left & right when you got a dirty air filter, and obviously that's not the case....
 

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Discussion Starter · #8 ·
Ok, so this is good info, guys...
DanM, the "P0068 MAF/MAP Sensor Throttle Position Correlation" description is the more generic one coming off the code reader. The Airflow description is the specific one for our cars.

I do not know anyone if the area (Raleigh, Durham, Chapel Hill, Cary, etc) with an RL. So, if anyone in the area wants to participate in a small experment, PM me.

BTW, when I cleaned the sensor, I used fuel injector/throttle cleaner, not carb cleaner. It is just like brake cleaner, but i think it might even be lighter/faster evap rate.

Also what is the part number/how much is a new MAF to try it out?
 

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ptparker said:
Ok, so this is good info, guys...
DanM, the "P0068 MAF/MAP Sensor Throttle Position Correlation" description is the more generic one coming off the code reader. The Airflow description is the specific one for our cars.

I do not know anyone if the area (Raleigh, Durham, Chapel Hill, Cary, etc) with an RL. So, if anyone in the area wants to participate in a small experment, PM me.

BTW, when I cleaned the sensor, I used fuel injector/throttle cleaner, not carb cleaner. It is just like brake cleaner, but i think it might even be lighter/faster evap rate.

Also what is the part number/how much is a new MAF to try it out?
Yah I hear you... the descriptions both mean the same thing. Are you 100% sure you don't have a vac leak somewhere, and that everything is installed correctly?? Not sayin I don't believe you, but a little leak between the intake and TB will cause a code like this real easy.... have you done the soapy water thing to look for leaks?
 

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Discussion Starter · #10 ·
DanM said:
Yah I hear you... the descriptions both mean the same thing. Are you 100% sure you don't have a vac leak somewhere, and that everything is installed correctly?? Not sayin I don't believe you, but a little leak between the intake and TB will cause a code like this real easy....

That is a really good thought... I will check it out... I looked at the joint where the two tubes meet, but I did not very carfully check the connection to the TB and the connection at the cone. It just sucks to have to take off the wheel/wheel well to get to that damn cone.

That would make sence, the connection at the TB being loose, b/c then air would be entering the system past the sensor... I will check it out tonight.
 

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DanM said:
Hey ***, Not to second guess at all. :) But from your post, you seem to suggest that it's a lookup table ("expected value") check. Are you sure that's the case?
Dan -No not an expected value table, but often with this type of DTC a table with an applied Pass/Fail tolerance to the "diagnostic" value based on exponentially weighted moving averages So when the correct conditions exist (ie enable criteria) the ECM runs the diagnostic, calculates the current "airflow" and then compares it to an expected value after applying a tolerance % range. It is this % range that could be different depending on the conditions, typically "tighter" when in the ranges most observed during the Federal Test Procedure, but may be more "relaxed" when outside of typical "road loads". Not all DTCs use this but many do, including the catalyst diagnostics.
DanM said:
The code description "P0068 MAF/MAP Sensor Throttle Position Correlation"
That DTC description is somewhat flawed as it was taken from a generic DTC reader. "Throttle Body Airflow Performance" is the official GM DTC title, but the true "diagnostic" rationale can only be observed from careful interpretation of the enable and fail cirteria stated in the diagnostic details in eSI (FSM)
DanM said:
<snip> seems to suggest that it's more of a MAF/MAP/Throttle rationality check, in which case you would think that the ECM would be able to cope with it just fine w/o failing (as long as none of the sensors were out of range).
Agreed. And this is a rationality check of sorts (as it's using numerous inputs to form parts of the diagnostic routine- not just as the enable criteria), but P0068s FAIL criteria is a bit one-sided, it will only set if the observed airflow is GREATER than expected/calculated. True,that ANY of the sensors used in the diagnostic routine could be out of range enough to result in an incorrect calculation and a FAIL, but usually there would be another DTC in combination then with the P0068.
DanM said:
I'm just wondering if maybe he has a leak/obstruction somewhere, or if the airflow through the MAF is unusual or something. Not ready to give up just yet, cause lots of ppl use intakes w/o problems! :)
Dan this is one of the most common DTCs that set when a "real" CAI is installed. Seen it LOTS on other cars including those with the regular 2.2 as well. The WORST part on the LSJ, is when it sets the ECM default action is to put the Throttle Actuation Control (TAC) system into "Reduced Power Mode" limiting throttle operation until the trip cycle is complete. In extreme cases (according to the FSM) it can even command the ENGINE OFF! (although I have yet to see it do this)

ptparker, do you actually have a scan tool that can read various diagnostic parameters or just a DTC reader? There ARE a few other things we can check that might be influencing the DTC- BARO, IAT, TMAP, SCIP and TP values should all be confirmed for accuracy and proper operation. Also what ECM calibration level are you at? 04 or 05? Have you had ANY updates??
HTH
Regards
WopOnTour

PS> Dan, did you get your SS yet?
 

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Not yet. :) Soon I hope. I didn't realize that that code was one-sided (only if airflow is too high). Neat! Good info.

I'd still check the basics first (like vac leaks) before I go pulling the intake off thinking there's nothing you can do about the code. I realize airflow codes are not uncommon, and that ETC applications are particularly sensitive to this sort of thing, but the ECM should be able to handle an incremental increase in airflow w/o throwing a fit.
 

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Mine still is a problem....our advanced diagnositics instructor and his whole class tried to troubleshoot the surging idle problem. They found a manifold pressure code, but nothing that wouldn't normally be there....the condition ONLY happens when the A/C is turned on, and even after the AC is off, the surging/stalling will continue until the engine is shut off and restarted....VERY bad news, these guys are the best, using their cool little Bluetooth PDA tools and all....impressive, but no headway for my problem.
 

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No offense Jim, but if they wern't using a TECH 2 with the latest release (NAO 25.003) software there is NO WAY they would be getting all of the PIDs and details neccessary to fully diagnose the LSJ. Blue tooth enabled PDA scan tools are cool and all, but there's no substitute for the real McKoy.
What actual DTC did you have in memory, and can you get me the Freeze Frame and Fail record data of the engine parameters that were occuring when the DTC failed. I'll see if I can help.
WOT
 

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i have no idea if this could even be correct but if you have a stock intake and turn the maf just a deg or 2 off then it will say not enough airflow right so if the maf is saying too mugh airflow cant you turn the maf just enough so it wouldnt throw the code. im sorry if this sounds hella dumb or whatever but i thought i read something in another thread about the maf being off by like a deg or so and it would throw the not enough air flow.
 

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jesus christ... so what i get out of this, is that in order for us to use a COLD AIR INTAKE, we need to, essentially, have our ECU's reflashed?
 

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You're trying to get something out of a 1/2 completed conversation... I have the CAI, and have been code free for weeks.... just keep reading and learning as it unfolds...
 

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DanM said:
<snip>I'd still check the basics first (like vac leaks) before I go pulling the intake off thinking there's nothing you can do about the code
ABSOLUTLEY! Good advice DAN. I would inspect your throttle body and supercharger mounting as well as your CAI
Barring that, get thee to a TECH2 or some other real" scan tool that will pull the FREEZE FRAME and/or FAIL RECORDS. These are "snapshots" of the sensor and engine conditions that were existing when the DTC ws failing. I could really use this information to help deteremine just what was happening at time of failure.
WOT
 

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With the way that the CAI uses thes rubber sleeves, there's some room for error there. I had mine attached at one point, without the tubes lining up correctly, and the sleeve still went on and would tighten down, but you could see that the seal was less than perfect. It took a few attempts to get everything lined up right and tightened down.
 

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WopOnTour said:
No offense Jim, but if they wern't using a TECH 2 with the latest release (NAO 25.003) software there is NO WAY they would be getting all of the PIDs and details neccessary to fully diagnose the LSJ. Blue tooth enabled PDA scan tools are cool and all, but there's no substitute for the real McKoy.
What actual DTC did you have in memory, and can you get me the Freeze Frame and Fail record data of the engine parameters that were occuring when the DTC failed. I'll see if I can help.
WOT
No offense taken - my instructor bud said he wished he had a Tech 2...I'll contact my Saturn dealer guy and see if he can figure it out.
 
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