Stock ECU vs Standalone ECU in your Subaru

Stock ECU vs Standalone ECU in your Subaru

Apr 15, '21

Warning - No aftermarket standalone ECU will pass an emissions test because they do not have OBD2 communications that would be required.

Update April 2022 with Cobb Green Speed
With ripple effect of the Cobb Green Speed update we've gotten a lot of requests for standalone ECU harnesses. Unfortunately we are still are not wiring up standalone ECUs due the same EPA concerns that brought about Cobb's Green Speed update. However, we decided to put in some of our knowledge here to help those who are looking into the pros and cons. We also wanted to remind people that no matter which ECU you choose our products should work just as they would with the Cobb Tuning Software prior to the update. If you have any questions, please ask us and we can help.

Prior to Cobb's Recent Changes
We had been living in a optimal world where we got all of the benefits of a standalone ECU without losing the stock ECUs reliability and ease of use because we could add additional logging (wideband), features (flex fuel) and upgrades (big turbos, injectors, etc.) while still utilizing the stock ECU. This created a scenario where we could build high horsepower cars while still keeping the reliability, user friendliness, and refinement afforded by the stock ECU. Based on that, there were very few scenarios where a standalone ECU would be better than the OEM Subaru ECU. Some common scenarios for standalone are below.


Common Standalone Scenarios:

  • 6 Cylinder (H6) swaps running a manual transmission

  • Racecars that requires a large amount of datalogging or engine protection

  • ​Non tunable ECU from factory (example: V1-6 JDM WRX or STi Models or Non Turbo Applications)

  • Engine swap into CANBUS car (example: 2013 WRX engine into 2010 2.5i Chassis)

  • Non Subaru Platform into a Subaru (example: LS into a 2010 WRX)

Current Stock ECU Limitations

With the Cobb updated tools with their tuning software the biggest current issue we see is datalogging and ECU adjusting based on an outside input. The 2 most common situations are when e-tuning and utilizing the rear 02 to log wideband input with the rest of critical engine data so that calibrations can be made without being local to the tuner. The other is flex fuel. Without the ability to bring in outside data, the ECU can't make adjustments for the changes in the ethanol blend.

The current solutions to the wideband problem is to log the wideband externally using a laptop (both of our AEM widebands could be configured to use the serial input) or utilize the wideband that your tuner will have attached to their tuning device or dyno. If you purchase our AEM Wideband with Gauge you can still have a display for you to monitor while driving even though it does not log to the ECU. If you have a standalone, both with and without gauge widebands could be configured to data log through the ECU just as you would with the Cobb AP.

As for the Flex Fuel there is not currently a solution for this with the Cobb AP. The closest thing would be to tune 2 maps, one for E85 (ethanol) and one for standard pump gas. We hope that Cobb will come up with a solution for this problem in the near future so we can have the safety and reliability that comes with the flex fuel sensor input.

Standalone compared to Stock ECU.

Pretty simply put, the difference is the ability to fine tune an aftermarket ECU to do one specific thing extremely well, while the stock ECU can handle any situation while maintaining engine performance and reliability.

There is no aftermarket ECU that can compete with the stock ECU in terms of ability to work in all conditions while maintaining reliability and refinement. The research and development dollars put into the stock ECU is likely to be greater than the dollars invested for all aftermarket ECUs combined. If you look at the number of inputs and outputs the stock ECU processes without issue (close to double most aftermarket ECUs when you consider cruise control and emissions equipment) you realize how sophisticated they are. Also factor in the base tuning that comes equipped to handle any driving condition from 120 degrees at sea level to minus 30 degrees at 10,000 feet you start to see that in action.

Yes, standalone ECUs have their place but the use case for them is fairly limited.

How should I decide if I need to run a standalone?

Depending on the number of modifications the threshold for standalone is probably lower than it was until recently. This will likely be a discussion between your tuner and mechanic to determine your goals and whether to reach them a standalone is required. This will be different for each project. Generally speaking it would be a scenario where there are so many modifications that retaining emissions equipment is no longer feasible and the car would be moved to a track only situation.

For now, we suggest doing whatever is possible to stick with the stock ECU. There are alternative tuning options for now like Opensource (Tactrix, Romraiader, ECUFlash, Carberry, etc.) and ECUTek. 

Cost needs to be factored in

Standalone ECUs are expensive. Yes, there are cheap standalone ECUs out there, but this is a scenario that is very much "you get what you pay for". Each ECU has a different number of open slots for inputs and outputs. The cheaper the ECU, the fewer inputs and outputs. This can present a serious problem depending on your application. Consider a dual AVCS STi with drive by wire. At bare minimum you'll need inputs for

  • 4 x digital input cam position sensors
  • 4 x Output for AVCS solenoids
  • 4 x Fuel injectors
  • 4 x Ignition coils
  • 2 x AVI throttle position inputs (main + sub sensors)
  • 2 x AVI accelerator pedal inputs (main + sub sensors)
  • 2 x Output for Throttle Body Motor
  • 1 x Output Boost Control
  • 1 x AVI Manifold Pressure
  • 1 x AVI Coolant Temp
  • 1 x AVI Intake Air Temp
  • 1 x Knock Sensor
  • 2 x Radiator Fan Trigger Output
  • 1 x Fuel Pump Trigger Output
  • 1 x Crank Position
  • 1 x Digital Input for flex fuel (usually this is a driver to go standalone)
  • 1 x AVI for Wideband (this commonly is CAN or built in to the ECU so it may not utilize an AVI)

Many of the lower cost ECUs do not have have enough inputs to even run this setup and many of the middle tier ECUs will be maxed out with the basic setup and you still haven't factored in any additional logging or features. 

Beyond the cost of the ECU and adapter harness, you will need a wideband so that the ECU can adjust properly on its own once the tune is done. The basic breakdown of cost for an Elite 2500 for a 07 WRX is below. Estimated total for a standalone, add ons, and tune time would be no less than $4,000

  • $2300 - ECU + Haltech Adapter Harness 
  • $300 - Wideband
  • $170 - Flex Fuel
  • $1500 - $2000 - Remember that even ECUs that come with preloaded maps will require initial setup to set base timing, adjust the map configuration to your specifics, actual tune time, multiple maps, etc.

I'm going to need to run a standalone, what do I do now?

If you determine the only solution to meet your goals is a standalone then you'll most likely need an adapter harness. Unfortunately this is not something we currently make however there are options out there. Below is a list by model type of ECU options. We did not list all the ECU options, only the ECUs that we think are worth looking at and have at least some experience with. This is not an exhaustive list and will get updated as we get more feedback since people will likely try more options in the coming months.

Note that some of the manufacturers like Haltech and Emtron are Austrialian based so their listed applications are slightly different than what we have listed below. That's because generally the JDM and AUDM markets are one model year ahead. 

Non CANbus cars are in this group and allow for more options on ECUs because there aren't the CANbus protocols back to the chassis to worry about. For more about CANbus click here.

JDM V1-6 (1993-2000)

  • Haltech - Plug and Play via Haltech Jumper
  • Link - Direct plug in board

JDM WRX and JDM STi 2001-2006 and USDM WRX 2002-2005

  • Haltech Elite - Plug and Play via Haltech Jumper
  • Haltech Platinum Sport (discontinued) - Direct plug in board
  • Link - Direct plug in board
  • AEM - Aftermarket jumper harness
  • Emtron - Aftermarket jumper harness
  • Motec - Aftermarket jumper harness

STi 2004-2006/Forester XT 2004-2005/Baja XT 2004-2006

  • Haltech - Aftermarket jumper harness
  • Link - Direct plug in board
  • AEM - Aftermarket jumper harness
  • AEM Series 2 (discontinued) - Direct Plug in Board
  • Emtron - Aftermarket jumper harness
  • Motec - Aftermarket jumper harness

USDM STi 2007/USDM WRX 2006-2007/USDM Forester XT 2006-2008

  • Haltech - Plug and Play via Haltech Jumper
  • Link - Direct plug in board
  • AEM - Aftermarket jumper harness
  • Emtron - Direct plug in board
  • Motec - Aftermarket jumper harness

CANbus equipped models require ECUs that have the ability to communicate with the car. Only a few ECUs have the Subaru protocols built in so the options for standalone ECUs become smaller. You will notice that on their websites they do not list the USDM market on their fitment lists. With CANbus, there are differences between the markets so their CANbus emulation can only be for what the manufacturer has available in Australia. From what we've found generally the CANbus protocols between models of different markets are the same but it's also worth noting that with the exception of the Motec we don't know any standalone ECUs that will 100% replicate all CANbus communications back to the car so that everything works. If you have one of these cars you may lose functionality of some features (traction control, SI Drive, DCCD, etc), so beware before you purchase depending on your expectations. 

Based on our experience the CAN protocols are probably the same from 2008-2014, but in 2015 and newer they change because it switches from high and low speed CAN to high speed CAN only. This means more features run through the CAN system and we haven't seen aftermarket ECUs updates their CAN protocols to meet this change other than Motec.

Legacy GT 2005-2006

  • Haltech - Plug and Play via Haltech Jumper

USDM WRX 2008-2010/Legacy GT 2007-2010

  • Haltech - Plug and Play via Haltech Jumper
  • Link - Direct plug in board
  • Emtron - Direct plug in board
  • Motec - There is a specific model for this application that comes with a plug and play harness when purchased through a Motec distributor.

USDM STi 2008-2010

  • Haltech - Theoretically this could be plug and play via the Haltech Jumper for the 2006-2010 WRX because the pin outs are almost identical and you were to add in the exhaust AVCS wiring into the Haltech jumper harness.
  • Emtron - Direct plug in board
  • Motec - There is a specific model for this application that comes with a plug and play harness when purchased through a Motec distributor.

USDM WRX 2011-2014

  • Haltech - Aftermarket jumper harness 
  • Emtron - Aftermarket jumper harness
  • Motec - There is a specific model for this application that comes with a plug and play harness when purchased through a Motec distributor.

USDM STi 2011-2021

  • Haltech - Aftermarket jumper harness 
  • Emtron - Aftermarket jumper harness
  • Motec - There is a specific model for this application that comes with a plug and play harness when purchased through a Motec distributor.

USDM WRX 2015-2019 - This is a direct injected platform so the number of ECUs that have the ability to drive those injectors is extremely limited.

  • Motec 142 - There is a specific model for this application that comes with a plug and play harness when purchased through a Motec distributor.

For the jumper harnesses we don't have any specific affiliation with any companies that do this so we do not specifically endorse the quality or accuracy of their product. That being said we have seen many people use for most standard ECUs and John Reed Racing for Motec adapters and ECU sets.