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GT86 Camshaft Position Correlation P0018

4/26/2018

19 Comments

 
Picture
GT86 Timing Chain
One of the most dreaded issues with the GT86 seems to be the camshaft correlation faults, with a wide range of codes from P000A to P0020 this problem can leave your FA20 feeling sluggish. Don't worry though, many others have had the same issue and it's not a mystery as to what's actually going on.  The reason the ECM sets these faults is due to a discrepancy in the crankshaft and camshaft timing. This can be caused by either a faulty OCV solenoid, misaligned chain, a faulty camshaft sprocket, and sometimes the ECM. 

Terminology

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GT86 VVT Description
Here you can see the VVT designations as described in the service manual. Bank 1 is always on the side with cylinder 1, so B1 is on the passenger side and B2 is on the driver side. Bank 2 Sensor A is the first sensor on B2(intake cam), and Bank 2 Sensor B is the second sensor on B2(exhaust cam). With this information, you can see our P0018 Bank 2 Sensor A code is directed at the driver side intake cam. 

Step 1 - VVT Initial Position Learning Values

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GT86 Initial Position Learning Value Specifications
Whenever a new ECM is registered to an FA20 equipped car, it has no stored learning values for the VVT sprockets. Even new cars from the factory need to perform a drive cycle before ​the ECM can "learn" the sprocket positions. Once these values are stored there is no way to erase or reset them, small adjustments can be made over long periods of time but that's it. This is why it's very important to diagnose these issues properly the first time. If you install a new ECM before the cause of the failure is repaired, you will need to replace it again and they are not cheap. Be prepared to transfer your tune software or license to the new ECM as well. 
Picture
P0018 Bad Learning Value
In the image above you can see what our problem cars learning values were, and right away you can tell VVT #2(intake cam Bank 2) is out of the specified range. The VVT #1(intake cam Bank 1) looks good and so do both of the VVT Ex(exhaust cam) values. At this point we know we have a problem with the driver side intake cam sprocket timing and we will need an ECM at the end of our repair. Let's move on...

Step 2 - VVT OCV

Picture
GT86 VVT OCV
The first part of the VVT equation is the oil control valve. This 2-wire solenoid is commanded via duty cycle by the ECM to control the VVT sprockets. The solenoid presses the button in the center of the sprocket, opening the passage and allowing oil to flow inside. The oil pressure from the engine flows through the camshaft and into the sprocket chambers, forcing the inner section (attached to cam) to "advance" in relation to the outside shell (attached to the chain). The duty cycle determines how far the solenoid opens, which performs either an advance, hold, or release action. 

So you can see just how important the OCV is, so let's start by marking our problem part with a sharpie as "B2A". Swap the Bank 2 sensor A solenoid and the Bank 1 sensor A solenoids, clear the ECM memory and perform a 10-minute road test. After the road test check for any pending codes, if you now have a P0016 then you have a bad OCV and it should be replaced. However, if you have the P0018 again like us then keep reading...

Step 3 - Inspect Timing Chain

Picture
GT86 FA20 Chain Timing Marks
Another possible cause of the cam correlation issue is jumped chain timing, I've seen it several times already and even on new unsold cars still on the lot! You will need to drain the fluids and remove the radiator and front cover to inspect the chain. Once you get access, turn the crankshaft clockwise until the key is at 6:00 and the triangles on each sides sprockets face each other like the image above. If any mark is not aligned properly then that is probably the cause of your issue, I would recommend replacing both sprockets and the tensioner on the affected side. There is no way to tell what caused the jump, and the amount of work it takes to do this repair are the reasons for my suggestions. You will need an ECM  to correct the learning values for this failure.

However if your timing is aligned properly like ours was, keep reading...

Step 4 - VVT Sprockets

Picture
GT86 VVT Sprocket
You can see in the picture above that there are many small parts inside the VVT sprockets. I do not know what part fails inside these gears but 90% of the time they are the cause of cam correlation issues. After verifying your chain timing is correct in the previous step, lock the tensioners with appropriate tools then go ahead and remove the chains CAREFULLY with the marks still aligned. The chains and guides are universal so you don't have to worry about mixing them up, the tensioners however, are specific. Once the chains are off, turn each sprocket by hand and be sure the cams feel smooth an free within the unloaded range. If all 4 cams feel the same and you dont find any damaged parts, go ahead and replace BOTH the intake and exhaust sprockets on the affected side. Again, you dont want to re-do this repair in the near future so be sure to eliminate the odds of accompanied component failure. I've learned this the hard way.

Reassemble the car being sure to double check the sprocket knock-pin alignment, torque the sprocket bolts, set the timing and verify chain is in the guide grooves, tensioner bolt torque, then clean ALL of the old silicon from the cover and mating surface. Install 4 new o-rings and put down a 1mm bead of silicone on the cover, get the bolts ready and wipe the engine surface 1 last time being sure no oil is there to cause a leak. Install the cover and torque the bolts accordingly, assemble the rest of the car and fill fluids. Clear the ECM memory and run the engine to purge the cooling system, then go on another 10-minute road test. When you return to check for pending codes, the P0018 should be there waiting for you. 
Picture
GT86 FA20 Bank 2 VVT Sprocket Install

Step 5 - ECM

Picture
The final step in this repair is to replace the ECM. The GT86 ECM is located behind the glovebox trim on the passenger side. You will need to remove the glovebox, and the surrounding trim to access the module. It is attached to a metal bracket and two 10mm nuts hold it in place. Once you install the ECM you will need to register it to the car, this process takes 30 minutes so have the battery on a charger. Once registration is complete, go ahead and do another 10-minute road test. When you return to check for pending codes again, at this time there should be nothing. 

If you decide not to replace the ECM, be prepared to reset the check engine light every two trips. Also be aware your car will be down on power since the ECM will be limiting you to about half the VVT operation. I hope this helps and don't hesitate to leave any questions in the comments or suggestions. 
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19 Comments
William Owen Wallace
10/14/2018 09:32:07 am

Hiya mate,
First let me say this is brilliant page with good information. Thank You!

Working on a 2013 BRZ in the states in my home shop in Florida, it was all smoke and mirrors until I found your page.

It has thrown the dreaded P0021/P0011 codes and it appears that it may be bad VVT control heads. Are there any special bits or tools need to remove the sprocket/control heads?

I found the engine was out of time physically when codes first appeared and engine had VERY rough idle and died. I pulled the cover plate and set timing correctly

I know that the engine is properly timed as I followed your instructions and then verified that timing marks all line up properly after initially setting them. It was a bit tricky but after several attempts was totally successful thanks to your tips. Ran engine and still threw P0011/P0021 DTC.

Cheers Mate

Reply
Tom
10/14/2018 07:46:39 pm

Hi,

The only special tools you need to replace the sprockets is the unique E-Torx socket.

https://www.ebay.com/i/163122155336?chn=ps

At the end you may still have to replace the ECM too.

Reply
John Sweeney
2/15/2019 04:07:13 am

Excellent info, thanks for the write up! Can you tell me what you used to verify the VVT Initial Position Learning Values? I'm getting P0016 and have swapped the OCVs, maintaining P0016, so I want to verify there isn't simply an ECM issue before pulling the cover. After resetting the codes, the engine feels strong with no hesitation and no idle surge.

Reply
Tom
2/17/2019 01:23:16 pm

I used the Subaru diagnostic tool SM3. You shouldn’t replace the ECM before checking the gears

Reply
ANDREW
4/4/2019 03:53:33 pm

Hey Bud,
Ive been fighting a P0018. Went through all the tests and didnt find anything wrong with the chain, but the B2 intake sprocket was very stiff in comparison to the other 3 sprockets so I replaced it. After waiting 5 days for the part to come in, I installed it and it was just as stiff as the one I replaced. I ordered another to verify and it felt stiff too. I reassembled anyways and the P0018 returned. After reading the article that makes sense, but should the new sprocket feel as loose as the originals out of the box?

Reply
Tom
4/4/2019 07:16:10 pm

You can’t really tell the condition of the sprockets with your hands(unless it’s broken). There is a oil controlled lock pin inside to keep it from spinning without oil pressure

Reply
Juan Cordova link
4/9/2019 10:27:23 am

Just like the guy Above ^^^ i too am fighting a p0018 code, only problem is my code has dissapeared but the car still feels as horrible as it does when the CEL and code are present, my guess is i have cleared the code so many times that now my ECM is thinking this is normal... when in reality it is not... i have swapped OCV's and cam sensors but for some reason the problem still persists. also it seems like my car is dumping fuel when i do just a slight amount of throttle. its weird it feels fine just before 3k rpm after that it just basically feels like a disaster.

Reply
Tom
4/9/2019 11:06:50 am

You should have your timing learned values checked, sounds like it’s off

Reply
Juan Cordova
4/9/2019 11:11:40 am

I am hoping to get my car into the shop in the next coming days. would you say that this seems to be a combination of the ECM/ and Sprocket issue?

Ulyses
7/12/2019 12:33:53 pm

Im doing a 2013 BRZ with a P0016 code which is the exact same but opposite bank.Ive replaced the cam sprocket(B1 intake)chains,guides and tensioners.Code came back obviously because of the learned values.Now my question is,when the sprocket is faulty and the learned values are now wrong,why doesnt the values change now that the sprocket is working correctly?
It adjusted the values to the bad cam vvt gear,why wont it change the values to the good vvt gear?

Reply
Tom
7/12/2019 07:19:31 pm

That’s a good question, the only answer I got regarding this from the SUBARU field engineers is:

the first time a new ECM runs the engine the Exhaust cam values are burned onto a ROM chip and used for reference. The Intake values are learned on the first drive cycle.

It’s a lame design

Reply
Logan Gantt
7/21/2019 07:18:42 am

Hello , do you have to change the ecu after changing the oil control valve as well ?

Reply
Tom
5/3/2020 06:09:49 pm

No, do the repair in steps to be sure you dont do more than necessary.

Reply
Alex Ngo
4/18/2020 03:30:23 pm

I am dealing with p0018 as well i don’t know where to start. I am boosted too yes. I would occasionally stall at times when at idle. Sometimes my exhaust pops but I’m assuming it’s from the tune?

Reply
Tom
5/3/2020 06:11:04 pm

Maybe, start with the diagnosis and see what you find.

Reply
MATT T HELANDER
4/23/2020 07:39:04 pm

Hey Guys, I'm also battling a P0018 / P0018 P and after replacing both Oil control valves on bank 2 I'm still throwing the code. Don't want to rip into the engine at the moment as I'm supercharged and there's a bunch of crap in the way, but any other diagnostic steps I can take myself? It's tuned on Ecutek.

Reply
Luis
4/30/2020 02:15:48 pm

I’ve replaced every vvti sprocket and ocv. Getting all new timing components. I know the vvti learned values are off. If I keep clearing the code even tho mechanically everything is working as it should will I still have a problem or will I still be down on power? I know I can tune the car to get rid of the check engine light and avoid having to keep clearing the code.

Reply
John
5/3/2020 05:31:04 pm

If you didn't replace your ECU, you'll need to flash to a different calid (I have heard this works but it's unconfirmed) or get a new ECU.

Reply
Tom
5/3/2020 06:12:45 pm

Yes the ECM will still limit power until you replace the ECM as well.

Reply

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