P1251. The Journey. The Epic. The Fix.

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LR 4WD Rear Locker
LR 4WD Rear Locker
Posts: 437
Joined: Sat Nov 17, 2012 9:56 pm
Town: Strand
Vehicle: '09 Hilux 3.0 D4D 4x4 AT
Real Name: Johan

Wed Apr 19, 2017 2:45 pm

I posted a reply on the other forum because someone else seems to have the same problem. Error code P1251 stepper motor intermittent.

The reply was supposed to be short, but instead I became the below. I was planning on doing a full writeup on the issue here but didn't get around to doing so. So here goes: :siffler:

It took me 5 months and a fair bit of frustration and cash to solve. I was very near to replacing a perfectly working turbo due to a inherent software issue on the 2009-2011 models.

I drive a late 2009 3.0 d4d AT Hilux 4x4. The first error was logged at about 197k km (will need to go look in the freeze frame data). I'm now on 204k km.

P1251 means that the turbo driver ( a small ecu and stepper motor driver in a box located in the glovebox ) is unable to reduce the boost pressure in the intake manifold quickly enough. It does so by telling the stepper motor on the turbo to reduce the pitch of the VNT vanes.

I did the following before I finally found a solution:
1. Replaced the stepper motor/actuator unit on the side of the turbo with one from a accident damaged 2014 d4d. No improvement. ~R1400
2. Replaced the MAP sensor on the intake manifold with a new unit from toyota ~R2500
3. Cleaned the intake manifold and EGR valve. ~R90 (Mr Muscle Oven Cleaner)
4. Made a blanking plate for the EGR valve pipe that fits against the block. ~R80 for oem gaskets
5. Swapped out the turbo driver unit in the glovebox with one from a 2007 fortuner (my dads)
6. Removed the turbo, cleaned the inside with oven cleaner and diesel. ~R450 for new oem gaskets,nuts and cir-clips

All of the above had little to no improvement and the issue steadily got worse. I have a dedicated laptop with techstream which I used to diagnose and reset DLC errors. I have in excess of a 100 freeze frames for this error. This I managed to get due to the vehicle going limp on every single drive towards the end. I was about to replace the turbo before chatting to Kosie Swanepoel from KSD.

7. The solution. A chip with a boost clamp.

Now for the Why:

I have a short exhaust that is very free flowing, makes a fantastic sound and causes the turbo to spool up rapidly. This however causes increased wear on the turbo actuator ring. This ring sits inside the turbo body and controls the VNT vanes. The turbo stepper motor moves this ring about with a little lever. This lever is a close running fit in the actuator ring. With time and use this fit becomes either too loose or too tight due to carbon or wear. This leads to a delayed reaction in boost reduction and ultimately a P1251.
I had this exhaust fitted in May 2016 and did a 12000km trip through Botswana, Nam, Zim and back without issue. Its only in the last 5000km since the trip that the issues have started.

P1251 gets triggered when the boost pressure in the intake manifold is in excess of 225 kpa for more than 3sec after a signal to the stepper has been sent to reduce the pitch. 225kpa being the gauge pressure and is also what gets recorded in the freeze frame data.

The boost clamp simply hijacks the signal that tells the ecu the boost pressure and tells it that the pressure is 224kpa (thumb suck figure since I don't know at what level KSD set this) instead. The signal to lower the boost pressure went to the stepper motor driver/ecu before we even got to the 224kpa level (its threshold is lower than 224 kpa ) so its already busy lowering the boost. This negates the risk of overboost damaging the engine or the turbo by telling the ecu the boost is lower than it actually is.

I have done a ton of reading on P1251 on numerous forums all over the world. It seems to be a common issue on AT models with different exhausts. But there are reported cases where it happens on vehicles with stock standard everything. It also seems to only affect pre 2012 models. The ecu and turbo driver have different part numbers post 2011.

My conclusion is the following: A free flow exhaust can lead to increased wear on the turbo actuator ring leading to delayed boost control. This delay and a too low error condition trigger level leads to a P1251 error and limp mode.

Also something to note. Once a p1251 and limp mode has been logged the next drive will be in a detuned safemode. I would purposely trigger a p1251 in the morning within a few minutes of starting up to get into this safemode on my way to work. This prevents a second error from happening until I reach my office. But on the following drive this detuned safemode would be cleared and a P1251 would be waiting to happen in the most inconvenient place. Interestingly enough even on this third restart after the vehicle would still not be back up to full power. So if you have a P1251 fault code logged your vehicle wont be running on a optimum power level. A techstream needs to clear this error before power levels (and economy) would be back to normal.

KSD fitted my Dastek chip with boost clamp on the 5th of April 2017 since then I have not logged a single P1251 or limp mode. Did a 1600km trip before and over easter up the West Coast and back without a issue.

It seems like toyota solved this issue in the post 2012 models since I'm yet to find one with this issue. Or it could simply be that models post 2012 are yet to get to a age where wear leads to this issue.

I will add more detail in time and some photos. And also post if the error returns...

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Mud Dog
Posts: 27228
Joined: Tue Apr 29, 2008 2:18 am
Town: East London
Vehicle: '90 SFA Hilux DC 4X4, Full OME, 110mm lift. Brospeed branch, 50mm ss freeflow exhaust. 30 x 9.5 Discoverer S/T's on Viper mags. L/R tank. (AWOL) '98 LTD 2.4 SFA, dual battery system. Dobinson suspension, LR tanks, 31" BF mud's.
Real Name: Andy

Wed Apr 19, 2017 3:11 pm

Interesting .... makes sense as well. Don't drive diesel, but I'm sure that other members will find this to be useful. Thanks for the input. :thumbup:
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LR 4WD Full Lockers
LR 4WD Full Lockers
Posts: 905
Joined: Mon May 07, 2012 12:33 pm
Town: Pretoria
Vehicle: Toyota Hilux 3lt D4D DC 4X4
Real Name: Marnus

Fri Apr 21, 2017 6:30 am

Thanks Johan. As usual a nice and detailed post that will undoubtedly help someone in future. What is a boost clamp and does that come as an additional item to the dastek chip?

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