ECU compatibility for 2000 OBW manual trans

[211]

Hi,
I've concluded that my ECU is causing erratic idle behavior and poor mileage and I need to replace it with a used one

This is a 2000 OBW, manual trans.

Wondering if an ECU from an Auto trans would work? They're more common.
Or should I locate an ECU from a manual.

This is the ECU i.e. computer under the RHS carpet

Edited May 23, 2022 by 211

[heartless]

no, an automatic ECU will not work for a manual without some modifications. has to do with the TCU input to ECU

i am more curious as to how you arrived at this diagnoses?  ECU failure is not that common. There are many other things that can cause an erratic idle and poor mileage.

 

[el_freddo]

I think you’d need to compare ECU pin outs manual vs auto. 

From the wiring looms I’ve cut down, I recall that the TCU needs are T’d into wires between sensors and the ECU. 

Cross reference part numbers and that will tell you more about what you’re up against. 

Before all of that. Look into the idle air control valve/mechanism. The rubber end on the plunger seems to get brittle and crack/wear in a groove that probably doesn’t supply the greatest seal when needed. 

Another thing, have you read the codes? I’d say that if you had an issue with the ECU you’d be experience more than erratic idle issues! 

Cheers 

Bennie

[211]

A while back I posted a thread regarding an all-4 cylinder misfire and system too rich condition.

Finally took it to a reputable shop where they spent 3 months (off and on) diagnosing the issue. They too were stumped.

It was the shop that narrowed the problem down to the ecu. They swapped in a known-good one and all the symptoms disappeared.

But to be clear. Prior to taking it in I did everything you could think of including replacing the Temp sensor, O2, IAC, everything I could think of that didn't involve pulling the motor.

The first thing the shop said to me was that it was the Temp sensor. The car thought it was -24 degrees out. I told them I replaced it already and it was unlikely the new sensor was bad. They quickly realized it was not the sensor and began digging further till finally shotgunning a new ECU in place.

Because they had the car for so long the shop didn't charge me a dime. But did give me direction on finding a used ECU on eBay. Its an easy swap I just want to make sure I'm getting the right one.

[idosubaru]

On 5/23/2022 at 11:32 AM, 211 said:

Hi,
I've concluded that my ECU is causing erratic idle behavior and poor mileage and I need to replace it with a used one

This is a 2000 OBW, manual trans.

Wondering if an ECU from an Auto trans would work? They're more common.
Or should I locate an ECU from a manual.

This is the ECU i.e. computer under the RHS carpet

Automatic ECU should swap fine.  Subaru used the same ECU between auto's and manuals for a loooong time.  That's why when converting an automatic to manuals trans you don't need to swap the ECU.

 

 

[211]

1 hour ago, idosubaru said:

Automatic ECU should swap fine.  Subaru used the same ECU between auto's and manuals for a loooong time.  That's why when converting an automatic to manuals trans you don't need to swap the ECU.

I just compared the pinout tables for both MT and AT ECM's
There's enough difference between the two that I'm more comfortable just finding the ECM for my exact model.
 

For instance:

MT- Intake manifold pressure sensor outputs 3.4-3.6Vdc (key on engine off) and 1.2-1.8Vdc (engine on idling)

AT- Intake manifold pressure sensor outputs 3.9-4.1Vdc (key on engine off) and 2.0-2.3Vdc (engine on idling)

There's plenty of other differences as well but that's the big one.

 

Edited May 25, 2022 by 211

[jonathan909]

4 hours ago, 211 said:

I just compared the pinout tables for both MT and AT ECM's
There's enough difference between the two that I'm more comfortable just finding the ECM for my exact model.
 

For instance:

MT- Intake manifold pressure sensor outputs 3.4-3.6Vdc (key on engine off) and 1.2-1.8Vdc (engine on idling)

AT- Intake manifold pressure sensor outputs 3.9-4.1Vdc (key on engine off) and 2.0-2.3Vdc (engine on idling)

There's plenty of other differences as well but that's the big one.

 

Sure, but since that's an input to (rather than an output from) the ECU, it suggests either a different pressure sensor or simply a different operating range (I'd tend toward the latter).  That doesn't mean a different ECU is needed, rather that the ECU just needs to know whether it's in an AT or an MT car.

Edited May 25, 2022 by jonathan909

[idosubaru]

4 hours ago, 211 said:

I just compared the pinout tables for both MT and AT ECM's
There's enough difference between the two that I'm more comfortable just finding the ECM for my exact model.
 

For instance:

MT- Intake manifold pressure sensor outputs 3.4-3.6Vdc (key on engine off) and 1.2-1.8Vdc (engine on idling)

AT- Intake manifold pressure sensor outputs 3.9-4.1Vdc (key on engine off) and 2.0-2.3Vdc (engine on idling)

There's plenty of other differences as well but that's the big one.

 

Okay. That works too. But there's no need to guess or research.  I have swapped MT and AT ECU's, and done engine/trans swaps. 

There's one pin on the car side connector that determines automatic or manual:
*without* that pin the ECU expects and runs as an automatic ECU
*with* the pin, it runs manual

All ECU's are the same, with no automatic or manual distinction, and the ECU adjusts accordingly based on that pin/wiring.  The manual trans ECU you buy will be the same ECU as an automatic.  The *only* difference is your body side ECU connector has one extra pin "telling" the ECU what it is. 

So when you convert an automatic transmission subaru to manual -  you swap the transmission and then just address that one pinout, by grounding that one pin - to "tell" the ECU it's now a manual.

It's that simple. And so is buying a manual trans ECU!

[211]

20 hours ago, idosubaru said:

Okay. That works too. But there's no need to guess or research.  I have swapped MT and AT ECU's, and done engine/trans swaps. 

There's one pin on the car side connector that determines automatic or manual:
*without* that pin the ECU expects and runs as an automatic ECU
*with* the pin, it runs manual

All ECU's are the same, with no automatic or manual distinction, and the ECU adjusts accordingly based on that pin/wiring.  The manual trans ECU you buy will be the same ECU as an automatic.  The *only* difference is your body side ECU connector has one extra pin "telling" the ECU what it is. 

So when you convert an automatic transmission subaru to manual -  you swap the transmission and then just address that one pinout, by grounding that one pin - to "tell" the ECU it's now a manual.

It's that simple. And so is buying a manual trans ECU!

Cool
Thanks for the clarification!
Gets a little confusing because there's just sooo many different P/N's. Add to the confusion, an exact match for my ECU on the used market is $300 but there's ones that (according to online Subaru parts stores) "matches your vehicle" for $100 used.

For instance, found one on ebay from a 2000 Legacy GT M/T H4 that's $119.

Guess I'll just pull the trigger and find out.

Any worries about an immobilizer buggering things up or is that not till later years?

[idosubaru]

32 minutes ago, 211 said:

Cool
Thanks for the clarification!
Gets a little confusing because there's just sooo many different P/N's. Add to the confusion, an exact match for my ECU on the used market is $300 but there's ones that (according to online Subaru parts stores) "matches your vehicle" for $100 used.

For instance, found one on ebay from a 2000 Legacy GT M/T H4 that's $119.

Guess I'll just pull the trigger and find out.

Any worries about an immobilizer buggering things up or is that not till later years?

Ahhh - Looking at Subaru part numbers explains your confusion!  Don't even look at ECU part numbers for Subaru!  It's a hot mess - for some unknown reason Subaru has always changed ECU part numbers every 46 seconds even back to the 1980's vehicles, when those ECU's are identical, from the same vehicles, and interchange with no discernable difference at all. 

No immobilizer or canbus issues until 2005+

Use www.car-part.com and you should find some $20-$50 ECU's.

their database is distorted by Subaru's part number systems as well, you just have to ignore it and work with the system a little.  Buy from an automatic and tell the person you call it's for an automatic so they don't get confused. 

car-part is far superior to ebay - much more product options and better pricing usually.  I've ordered probably a triple digit number of parts from various stores all over the US on car-part.com, they're all very accustomed to shipping parts.  I have two boxes on my porch right now found through car-part.com.

You can also order from preferable areas - like maybe buying an ECU from a less humid environment like Colorado or the SW is ideal for electrical components?  Colorado is one of my favorites because they're usually very familiar with Subaru's, no rust, and almost never over priced. 

[idosubaru]

In reference to my last post - the first ECU I found on car-part.com was $50 for your car.  Better than the prices it looks like you're getting elsewhere.  It was also from Colorado which has some plusses to it as I mentioned. 

[211]

24 minutes ago, idosubaru said:

In reference to my last post - the first ECU I found on car-part.com was $50 for your car.  Better than the prices it looks like you're getting elsewhere.  It was also from Colorado which has some plusses to it as I mentioned. 

Awesome! Thanks for this

[idosubaru]

32 minutes ago, 211 said:

Awesome! Thanks for this

Sure thing. Hope it solves your issues.