So I was out preparing for the track day, coming up next weekend, and during one of my 120 mph runs, the SES light came on. I came to a stop and noticed that the idle seemed to be stuck at 2500 rpms. I thought maybe a hose came off or something, so I turned the motor off and investigated. I couldnt find anything loose, or leaking under the hood, so I restarted the car. Fortunately the engine idle had corrected itself, but the SES light was still lit.

So, I pulled the code and found I had thrown code P1235. This turns out to be the code for Mass Airflow Sensor Plausibility. Well crap, this tells me nothing, so I look in the service manual and find that its a comparison between the actual measurement of VE by MAS signal with VE estimated from the TPS signal. The equation is |Calculated Ec(TPS(Main))-Calculated Ec(TPS(sub))| < 8.8%. If this is true, then the check is made again for 360ms. If it remains true for this entire time, the system forces a malfunction, and goes into a safe mode by disabling the MAS.

Personally, I think this system is crap, and I can see having a lot of issues with this once we up boost and the MAS starts reporting air flow much higher then the car expects from the estimated values given by the TPS tables, that are probably stored on the ECU. I have never seen this before, so I am hoping someone out there may have more input on this from other vehicles maybe.

For the record, my car is pure stock, with no modifications. Well it was when I had this issue. I just installed a MBC today, and I have a feeling this will show up again. If someone wants to try and reproduce this, get to about 110 and flip into 5th and floor it. Thats how I got it.

BACKUP INFORMATION:
According to the Service Manual, the most likely causes for this error is the following:
- MAS system failed
- ECM Failed

Thats not too encouraging

 

question off the subject when you put the mbc on did you get a cel. I just put mine on this weekened and it threw a code. Do you have any of the boost control solenoids connected. I had to hook 1 line back to the upper intrcooler pipe and the other to the maf to keep the light off. Any help since you just put one on

 

I havent thrown a light since I put the MBC in. I dont currently have the stock solenoid connected to anything. What was the code you were throwing?

 

Keep us up to date on this one PDXEvo.

 

My ses light came on for the second time and had it checked, the same code as yours p1235. My light never started coming on till i put on the mbc. Somebody help us.

 

Uh-oh..

 

Wow, this sucks. Hopefully its just a one time case, but that would be even stranger. Keep us all updated.

 

If it was the ecu seeing too much boost, you think it would have happened to all these shops adding all their parts and increasing the hp without any tuning.

 

Has AMS, Turbotrix or Buschar seen this problem?

 

I have nailed this down to being a 5th gear thing. Its definitely amplified by the addition of a boost controller though, and I can get it to consistently throw a code by just flooring it in 5th gear at lower RPM's. Since the addition of the boost controller is allowing the car to hold 23psi really solid in the low RPM ranges, and in 5th gear you stay in this range for quite awhile, its allowing for this mis-match to occur. I wouldnt say this is a critical issue, but the problem is, after it has occured, you need to "re-boot" the system by turning the car off and back on. After several minutes of correct operation, after the re-start, the light will auto clear too.

Once we have PCM editing tools, I believe this will be a simple fix as all we will need to do is change the comparator table, assuming its editable.

 

Not necessarily since the tuners are doing very short runs on a dyno probably only in 3rd gear. Sounds like PDX was out on a track and only happens in 5th gear when pushing the car hard.

Hopefully it gets figured out and isn't a computer gremlin safeguard that will throw the car into safe mode when pushed hard. That would totally defeat the purpose of this car being used on a track

 

Unfortunately the car goes right into safe mode, which means it turns the MAS off, and uses TPS position for everything. Car idles at 2.5k in this mode, but is easily resolved by pulling over, and restarting the car.

The issue isnt occuring at WOT pulls, fortunately, so I am hoping to avoid this issue on the track entirely. I will also be turning the boost down from 22-23psi peak to 20-21.

 

Some of the tuners have mentioned the CEL/limp mode when turning the boost up too high. TT mentions it a bunch of times in this thread: https://www.evolutionm.net/forums/sh...ight=boost+cut

Obviously there are additional safeguards built in to the ECU that will have to be worked around to avoid the limp modes, most likely with software ... although TT mentions that they found a work around and I don't think they have software yet ...

It shouldn't happen in stock form though obviously, although of course you are likely to see the most boost in 5th gear, going uphill, at low RPM due to the load ... best advice for now is probably not to do that

 

Good find PDXEvo!

 

I was in 4th gear low rpm building boost when mine came on