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16 Bit ECU vs 32 Bit ECU in your Subaru

In this blog post we talk about the differences between 16 Bit ECUs and 32 Bit ECUs and how these differences affect your swap. We are sticking to turbo platforms for the purposes of this blog.

What is a Bit?

A bit is the smallest element of computer storage (0s and 1s). A good way to picture how the bit relates to an ECU is to think about Nintendo. The first Nintendo console used an 8 bit processor so it could process 8 bits at a time while the advanced N64 could process 64 at a time. So the higher the number of bits, the more data that can be processed. In terms of video games that means better graphics. In terms of an ECU, that means more information can be sent and received.

16 Bit vs 32 Bit ECUs

As Subaru added more features to the cars (DBW, Immobilizer, etc) more processing power was needed so Subaru upgraded the ECU to handle that. The most important thing to note here is that the 16 bit and 32 bit platforms are NOT interchangeable. The problem comes down to the way that Subaru set up the ECU to send and receive information changes between these two models. The biggest identifier between these two is the cam position sensor type.


Which ECU do I have?

16 Bit features

5 ECU Plugs

2 Wire cam position

Cable throttle (exception is the JDM Forester drive by wire models, but it still uses the 2 wire cam position sensors)


Common platforms with this ECU:

02-05 USDM WRX

01-07 JDM WRX

01-07 JDM STi


32 Bit features

4 ECU Plugs

3 wire cam position

Drive by wire throttle


Common platforms with this ECU:

2004 and newer STi

2006 and newer WRX

2004 and newer FXT

2005 and newer Legacy GT/Outback XT


16 Bit to 32 Bit Conversion

There are essentially two ways to go about this conversion:


Don't recommend - The quick and dirty way is to bolt on the old intake manifold and harness to the new long block. For example if a 2005 STi engine is put in a 2002 WRX, the WRX intake manifold and harness could be bolted to the STi longblock. The AVCS would not function but with a tune the engine would run.


Do Recommend - A harness merge so that the new 32 bit ECU and engine wiring is installed in the original 16 bit body harness of the chassis. This will make sure all desired features from the new engine work like AVCS. For example the same 2005 STi engine is installed complete in the 2002 WRX, but then the WRX harness is sent to use to modify it for the STi ECU, STi engine plugs, and we'll also convert it to drive by wire so the harness will plug back into the WRX chassis just as it did before but also has the necessary connections for the STi ECU and engine. Click here if you want to see merge options - https://www.iwireservices.com/subaru-harness-merging


32 Bit to 16 Bit Conversion

We do not recommend this conversion. Not only is it a downgrade in ECU technology, but the camshaft position sensors won’t match which means the engine most likely will not run. In addition, depending on where you live smog could be a concern because when the ECU is scanned, the scanner will recognize it as an older ECU than what the car was designed for.


If you have a 32 bit platform, look for a replacement that is also has 3 wire cam position sensors in the head - https://www.iwireservices.com/post/my-subaru-engine-blew-up-what-should-i-replace-it-with

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