TC + CEL light on high rpm deceleration

[Agent_D]

First post on the fourm. Got a 2013 Subaru BRZ Limited about a month ago now. 12k miles, and had to fix a few very ghetto things the previous owner did to the car.

After going through quite a bit of fixing/replacing stuff that the previous owner did improperly; I've finally gotten the car to a point where it runs, and drives very well. I've gotten all the old CEL codes resolved, and now I'm stuck with only one. Whenever I downshift to decelerate; if I'm above 4500rpm, the TC light will flash for a second, then the CEL will come on and give a code for MAP sensor low input voltage. After hours upon hours of searching for this issue; I was only ever able to find one instance of this happening (at least on google/car forums) on a Honda. The guy ended up finding out that the Honda VSS unit was causing the issue.

So, my question is. Would that be viable in this situation? Could the VSS be throwing this CEL on high rpm deceleration? I don't really mind it that much, but it's just a small annoyance I'd like to solve. It doesn't affect the cars performance at all; everything works normally even after the CEL comes on from the circumstance.

I'm fairly mechanically savvy, and can do any of the work that needs to be done. This is just a new adventure, as I'm coming from owning a 2nd Gen RX-7, to a new car that has all the fun gadgets. Learning experience, but oh what a fun car; and very reminiscent of an FC3S for me (at least how the car feels in terms of driving, and the quirks).

Thanks for any information!

[jasonojordan]

Does it to it with the traction control turned off completely?

[Agent_D]

Yes, I've tried it with the VSC off button, and the Trac off buttons. While I haven't researched the car a ton yet; my Trac off automatically turns back on after 30mph (I'm assuming this is normal). So with VSC off, and Trac off; I've tested at over 4500rpm decel in first gear, and with vsc off, tested in other gears all with the same result.

On a side note. There are times I've decelerated from 7k rpm testing out this problem, and had the TC light come on for several seconds before the CEL triggered. I was assuming that this was possibly related to the LSD, and decelerating from higher RPM; though I don't believe the BRZ torsen unit is a 1.5way LSD.

I do know that the previous owner had messed around under the car; there are aftermarket rear control arms, and what I believe to be aftermarket diff mounts. Would it be possible that poorly installed, or improperly installed, diff mounts may cause something like this? I believe it also may have an aftermarket clutch/flywheel combo, as the car seems to rev much more quickly than others I've seen, and the clutch is quite odd feeling (not in a bad way). Possibility that any of a combination of those things may contribute? I'm a bit in the dark when it comes to the newer systems, and what may make them pop lights/codes.

[jasonojordan]

no its not. Hold the trac off button for apx 10 seconds and it will turn the system off till you power cycle the car.

[Agent_D]

So I went out and did a little more testing. 1st, 2nd, and 3rd gears; if I don't go above 5k rpm to decelerate, the situation does not occur. When I go over 5k, and then start decelerating, the TC light will flash, and the CEL comes on when the decel rpm gets to around 4500-4800rpm. I ran Torque with the logging enabled on this little test to see if it will give any useful information in the log.

[zc06_kisstherain]

sounds like something is triggering on sensors that indicates that TC light is on.
maybe sensor issue on TC/VSC?

[mav1178]

Originally Posted by jasonojordan

no its not. Hold the trac off button for apx 10 seconds and it will turn the system off till you power cycle the car.

Only way to turn off electronic aids until the next time you start the car is to do the pedal dance.

-alex

[jasonojordan]

So what is it doing then by holding the trac button for 10 seconds? turning most of it??

[[YOYO]]

Originally Posted by jasonojordan

So what is it doing then by holding the trac button for 10 seconds? turning most of it??

Yah. It's a bit deceiving that way. It's like you say, 'most of it'. Sounds like a really odd problem that you're facing. Best of luck with figuring it out

[jasonojordan]

Good to know. Thanks for the incite.

[[YOYO]]

If it ever becomes a concern / something that you are looking to do, this is a thread link to the 'pedal dance' -

http://www.ft86club.com/forums/showthread.php?t=25494

Also, a company called Beastronix Racing has developed a module that allows for the e-nannies to be completely disabled with the press of a button. Essentially, a pedal dance in one switch.

http://www.beastronix.com/blog/

[mav1178]

Originally Posted by jasonojordan

So what is it doing then by holding the trac button for 10 seconds? turning most of it??

It will turn it off for about 95% of the driving you would normally do.

Pedal dance puts the car in diagnostics mode with everything except ABS disengaged. It's perfect for purposes of trying to isolate a problem as described in this thread.

Also useful if you want to drift the car or otherwise not have any electronic aids mess with pushing the car to its limits.

-alex

[justatroll]

Let me guess, you have an aftermarket Intake?


Do you have a tune? (If you had a tune, would you know?)


Sounds like the rear suspension mods are messing with the VSC/TCS.
Have you had an alignment done? Checked tire pressures?


The MAF sensor reading being wrong at high RPM sounds like a MAF conversion needs to be tweaked (why I asked if you have an aftermarket intake).

[Agent_D]

Thanks for all the replies so far. I do not have an aftermarket intake. I have a Perrin inlet tube, and K&N filter in the stock box. The problem was present even before the Perrin inlet tube was installed.

The problem presented itself last night while decelerating at 2500rpm in 4th gear multiple times; though did not trigger the light today under the same circumstances.

I was assuming there may be a tune that I'm unaware of. As soon as I can, I'm going to get an ecutek kit, and map sensor to see about that as an issue.

In the meantime, I will be inspecting the tranny/diff as far as I am able without removing them completely as soon as I can to check for any issues there.

When I got the car, it had a cheapy $10 ebay oil catch can that was installed with the improper lines, the lines were both fully collapsed, so nothing was able to get through the PCV line. I have replaced that with a radium catch can kit, and new OEM PCV hose (I also ordered a new PCV just in case, and will replace that as soon as it comes in). It had a splitter on the brake booster line that was going to what I assume may have been a "boost gauge" or some kind of atmospheric pressure gauge (since it shows no signs of having had a turbo, or supercharger installed anywhere), and it was just lying open causing a vacuum leak (that has been fixed).

I have not had an alignment done, but it does have ISC N1 basic coilovers, and the car drives perfectly, no pulling or weirdness in the feel of steering/braking/etc. Tires are at 34.5-35.5psi (though the TPMS sensor light is on because the in car sensor is not receiving a signal from the TPMS sensors in the wheels, which I assume is an easy fix by having them recalibrated at the dealer). The only other thing I've noticed, is that the car has very bad diff shutter/wheel hop when launching, even at around 2500rpm, and if I drop the clutch at around 5k rpm, the tranny/shifter moves a LOT more than I feel is normal.