Mitsubishi Lancer Evolution Forum banner

SES Light during brisk driving

2699 Views 16 Replies 11 Participants Last post by  DVDee
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.

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

Thats not too encouraging :(
See less See more
1 - 17 of 17 Posts

I have a feeling that Mitsu engineers need to tweak this ECU a bit more.

I have a feeling that Mitsu engineers need to tweak this ECU a bit more.
Does this feel slightly familiar to you?
1st alot people geting erratic idle on warm start. Now Stuck idlel at 2500 rpm?
everything seem fine with the JDM guys. but for us. Bad OEM flashed ECU that delayed the MR. Nothing major on any mechanical parts.beside people complaining about notchy gears. ECU is an easy fix, but it need to come sooner. Bad ECU can lead to other mechanical problems later on.
The reason the idle stuck at 2500rpm's is because the car went into a safe mode loop that ignored all inputs from the MAS. "Rebooting" the car fixed the issue, but doesn't clear the SES light. You have to do that manually. The service manual states that the most probable cause for the issue is a bad MAS. My dealer was all for ordering a new one, but I want to see if the issue re-occurs first.
This has happened to me twice now since the mbc install. Both times I was WOT when the CEL came on.

Also, upon receiving this CEL, If I'd let the car idle, it would idle at 2000rpm. Just like PDX said, turning the car off and on fixed the idle.
bugger! keep us updated. Im ready to start my mods shortly once the cars back from the panel beaters.. not good to hear.
This is occurring because your boost levels are too high for whatever your throttle position is. Going to the Unichip and a EBC (which is part of the unichip) has fixed this issue for me! The Unichips boost control is much more accurate and smooth then the MBC is.
I experienced the same issue you had when I was screwing around with my MBC running to high boost. I set my boost lower asap pulled my battery for 10 min and SES cleared.

What boost were you running right before SES on?
I was spiking to 25psi and settling at 18/19
The JDMs get the same problems when they changed to EBC..

It happens on part throttle low rpms high load
PDX is this repeatable? Can you do it on command when going from 110 to 5th and flooring it every time? If so then it stands to very good reason that there is a design flaw somewhere in the system and it would be mitsubishi's fault. If it's intermittent it is probably something they are willing to over-look until it becomes a wide-spread problem with lots of owner reporting it.
I'll see if I can't get out tonight after work and try to replicate the issue. This doesn't sound good.

On a slighlty related topic that I would like to have others test. I was sitting at a stop light yesterday reving the engine. As I let the revs fall back to idle, suddenly the ASC off light lit up and the warning associated with it popped up along with a "service soon!" warning. I tried turning the ASC off/on without any change. The stop light turned green so I drove down the street to my condo. The warnings stayed on the whole time. I turned the car off then on again and it was all reset. I replicated the problem immediatley after. I tried it a third and fourth time with no success. Anyone else run into this problem? I would be interested to see if anyone else has the issue. My car is stock.
I've had the same thing happen as well Evolutionary.
This isn't a design flaw really, its throwing the code by design. Like Gunzo posted above, this problem generally arises at part throttle operations where you will build boost quicker then you would if you were using the stock solenoids. In this case, the car believes there is a problem since the MAF is reporting a flow higher then what the ECM thinks you should be getting at part throttle, where your TPS is relatively low. The car has a table that it compares its expected flow rate against your actual and your TPS, and if the variance is too high, you through this SES light. Since the primary reason for this failure would be a failed MAF sensor, the car then goes into a safe mode and drives pretty poorly.

I dont believe there is anyway around this when using a MBC, but with an EBC you should be able to adjust your boost in different gears to prevent this.
Do you guys think that the reflashes done by Ecutek help avoid these problems?
1 - 17 of 17 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.