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2002 EZ30 H6 into 1999 Outback swap

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We're swapping an EZ30 H6 out of a 2002 Subaru Outback sedan into my 1999 Subaru Outback (EJ25, five speed manual).


For more info on the car, check out my build thread:



This is the most helpful thread on this swap I've seen:


You will also want to download the factory service manual (FSM) for your donor car, and probably the car you're putting it into:



There are four ways to get a running H6 Subaru.  For engine or trans swapping purposes, the 2001-2004 non VDC cars are the simplest.


The easiest is just to buy a decent H6 Subaru.  I would recommend this, if you want a manual trans, swap one in, you'll probably need to swap the rear diff too, still less work and expense than an engine swap.  This post and the links above will help with the wiring side of that.


The next easiest is probably to buy an engine from a junkyard and use a standalone ECU.  The money and time you'll save by not buying a complete donor car and removing the wiring will probably pay for the standalone.  As I understand it, this is the only way to use a later EZ30 or EZ36.


I bought a donor car and we pared down the wiring to the minimum needed to run the engine with no codes and keep the cruise control and alternator working.


It seems like a lot of people, including in the thread above, do a harness merge.  This involves taking the harness out of both cars and combining them into one.  This would definitely be less wiring to fit in the car than the way we did it, but you'd really have to know what you're doing and be confident you're not going back to the stock engine.


This first post will cover the wiring.  By far the biggest headache is the wiring, especially since it means removing both dashboards and HVAC systems to get at it (and putting one of them back in eventually).  This part of the swap took us at least two weeks, but a lot of that time should be reduced if you follow this guide.

Starter wiring is the same.
The wires for the ignition switch on the 99 plug right into the harness of the 2002 even though one is four pin and the other is six.

The transmission and instrument panel wiring do not match the FSM, so that added to the challenge.


Seemed like the main reason to have the dash plugged in was the alternator wouldn't charge without it and it would cause the fuel level code.  The FSM showed one of the wires going through the battery idiot light.  So I wired a resistor instead, alternator charges and no fuel level code (usually) with this.  Spliced the green/white wires coming out of that blue plug in the front of the 2002 interior fuse block through a resistor to that second pin over on the SMJ (black/white wire).  Bottom line, you need to have 12V (switched on with ignition) going to pin 1 (black/white wire) of the alternator.  I had a 47 ohm resistor between the 12V ignition source and the alternator.  I believe that circuit opens when the alternator starts charging, which normally turns off the battery idiot light.  When we put this in the 99, I wired the black/white wire from that instrument panel (pin 8 i10, about the middle of the left hand connector) to the black/white wire coming from the 2002 alternator.




Even if the battery idiot light burns out, there is a diode going to one of the other circuits in the instrument panel that will keep the alternator charging the battery.


One of the last things I did before we pulled all the wiring out was to figure out the feeds for the various gauges and idiot lights.  Debated putting the 02 instrument cluster in the 99 but physically it's surprisingly different and electrically it will probably be simpler to keep the 99 instrument cluster.


So, again using the FSM, figured out the CEL/MIL, oil pressure idiot light, and temp sender (for gauge).  The 2002 FSM seems to have the right wire colors but the pinouts for the instrument cluster are different than the actual gauges.  Some of them were easy to confirm by testing for continuity on the well labeled circuit board to the pins on the top of the instrument cluster.  Final confirmation was cutting them and then grounding the CEL/MIL and oil pressure to see them light up.  Also put a resistor between temp gauge and ground to see the needle move.  Do not ground the wire for the temp gauge, it will cause the gauge to shoot all the way up and stick there until you take the cover off the instrument panel and unstick the needle.  Oil pressure switch is green/orange, MIL/CEL is red/white, and temp is pink/white for the 2002 EZ30.




Also figured out which wire to cut to kill the tach but still read on the OBDII scanner, same with the speedo.

Near the ECU I spliced those to the wires coming out of the 99 EJ25 ECU. 
The black blue wire at pin 64 (third row) of the EJ25 ECU goes to the tach.  I wired this to the output of the tach adapter.  Pin 9 B136 of the EZ30 ECU is an orange/white wire that I ran to the input of the tach adapter.

The red green wire at pin 58 (near center of third row) of the EJ25 ECU is grounded when the MIL/CEL is on.  So I spliced that into the red/white wire coming from the EZ30 ECU.

I cut the wires going to the oil pressure switch and temp sender for the EJ25 and spliced wires from those to the corresponding senders for the EZ30.  They both are on connector B21 going to the EJ25 engine, the pinout is as follows:

-  -  -  -

-  -  -  -

9  10  -  -

Pin 9 is green or green/white depending on which side of the connector you're using.  It is grounded when the oil pressure is low.  Connect this to the green/orange wire for the EZ30.

Pin 10 is violet or white/green and goes to the temp sender.  Connect that to the pink/white wire for the EZ30.


I didn't wind up doing it this way, but since the 2002 FSM is inaccurate regarding the instrument panel wiring, here is a little info on that.  Looking at instrument panel where i12 plugs in:

-  -  -        3  -  -

-  -  12  -  -  9  8  -

Pin 3 is green/white and has 12V with the ignition on, powers the various gauges and idiot lights.

Pin 8 is pink/white and goes to the temp sensor.

Pin 9 is black/blue and goes to ground.

Pin 12 is red/white and goes to the MIL/CEL pin on the ECU.




The main code we kept getting was the fuel level code, P0463 I think.  Eventually I just wired the brown / white wire that went to pin 27 of the 99 EJ25 ECU to pin 25 B135 (brown/black?) on the 2002 EZ30 ECU.  It seemed with everything hooked up this would get 3V but when we tried to just give the EZ30 ECU 3V at that pin we'd still sometimes get the code.  The picture below also shows the tach adapter.  That was very easy to wire up and works great.  At the top of the picture are the 10W resistors we wired to the TCM so it thinks it's still hooked up to solenoids.  I would recommend 1000 ohm 10W or they will get pretty hot.




If you want the wipers, power mirrors, and other accessories to keep working on the Subaru you're putting this in, you'll have to power both the ignition and accessory circuits.  Easy way to do this is to go from the big green wire in the 2002 harness (see below for a convenient place to shove a spade terminal in that) to the harness of the car you're putting this in.  The 99 has a four pin connector B72 for the ignition switch.  Since we'd plugged the ignition switch from the 99 into the 2002 harness, the 99 harness end was just hanging loose.  It has four big wires, black yellow, red yellow, red, and blue red.  Red yellow and red are for accessories and ignition, so we plugged 12V ignition into both of those.  On a side note, the turn signals won't work if you don't have the hazard switch plugged in.




Another code we got before we were done was P0452 (evaporative).  There are four important wires going to the back in one connector that will cause trouble codes aside from the fuel level.  We traced them back to the ECU and wired in some resistors as follows.

If you don't have the red/light blue or black/yellow wires hooked up, you will get P0183 fuel temp sensor A circuit high.  There is normally about 3.5k ohms between these, so I wired in a 3.2k ohm resistor.

The green/black wire disconnected will cause a P1400.  The brown/yellow wire disconnected will cause a P0447 evap emissions vent control circuit system open.  These both seem to want voltage.  There are various green/black wires running around the harness that are 12V with ignition on, perfect for this.  Make sure to get one of those and not the VSS though.  I went from the green/black 12V to a 3.9k ohm resistor.  I spliced the green/black and brown/yellow wires to the other side of the resistor.



After we put the 2002 harness in the 99 my friend realized we only needed a few fuses on the interior 2002 fuse block, so we cut that down.  Here are the fuses we needed:

13 fuel pump




17 fans

18 fans & cruise  11 ignition



gray connector

1BR    -    -    -  -

6BL    -    8G    -  -


ignition connector

-  -  -         -  5GR

-  -  -  -  -  -  -


gray connector

1GL    2GL  3GB

-       -    -       -


white connector

1GL    -  -

-  5GB  -  -


blue connector (front of fuse block)

1GB  -  -             -  -

-  -  -  -  -  -  -  -  -


The big green wire, pin 8 of the first gray connector, supplies fuses 11, 17, and 18.  The black red wire, pin 1 of the same connector, supplies fuse 13.

The other side of fuse 11 goes to the green red wire, pin five of the "ignition" connector.  I forget what color that one was.

The other side of fuse 13 goes to the black blue wire, pin six of the gray connector for the fuel pump.

The other side of fuse 17 goes to the green blue wires, pin one and two of the other gray connector.  This is for the fan relay and sub fan relays 1 & 2.

The other side of fuse 18 goes to three green black wires.  One is pin three of the gray connector for the main fan relays.  Another is pin one of the blue connector for the cruise main switch.  The third is to pin five of the white connector for the cruise control module.


Main fan is driver's side, sub fan is passenger side.

To test the fans, you can put a resistor in place of the temp sensor.  This is the pinout looking at the harness plug:

black/brown    brown/red


The black/brown has 5V from the ECU, the brown/red is the temp signal to the ECU.  The temp sensor reads about 3k ohm at room temperature.  I put a 1k ohm resistor in the harness plug and the ECU reads 109F.  Anything under 120 ohms seems to read 210F and should turn on all the fan relays.

The brown wire at the bottom of the plug is just for the gauge.  That pin on the sender reads about 1k ohm to ground.



Didn't wind up cutting or splicing any wires for the OBDII connector, but there are really only four pins on it that matter.  A few times if we didn't have the grounds for the TCM hooked up it didn't work.  Here is the pinout looking at the connector:

BR -  -  -  -  -  -  -  -

-  VG  -  W  W  -  -  -

The black/red is 12V with the igntion on, comes from the main relay I think.

Violet/green is the signal wire that should go to pin 21 B134 on the ECU.

The whites should be grounded.



It was somewhat difficult to keep the cruise control working.

The brake pedal switch is normally closed going to the cruise control module (CCM).  Easiest solution is to short this.  I did eventually wire it to the 99 brake and clutch pedal switches so it turns off if you hit either of those pedals.

The green black wire that goes from the transmission control module (TCM) to the CCM pin 3 is for vehicle speed.  I cut this at the TCM and connected the VSS from the 99 five speed to it so it sends a VSS to the ECU (pin 1 B134), speedo, and the CCM.  The 99 VSS has three wires, I believe they are red/black = 12V, green/black = signal, and black/red = ground.

The speed sensors in the auto trans must have a different output.  Originally I'd wired the VSS from the manual trans to VSS1 for the auto trans and never got a VSS out to the speedo/ECU.

Didn't keep the cruise from working, but we'd get a cruise set code with black orange wire connecting the TCM to the CCM pin 3.  So I cut it and so far cruise works and no codes.


There is quite a bit of wiring involved to keep the TCM, and therefore the ECU, happy.  One of the big hassles with figuring this out is that the 2002 FSM only shows the wiring for VDC cars, and that TCM has three connectors whereas ours has only two.  So the pinouts are completely different.  The 2001 FSM seems to have the right pinouts in the circuit diagrams but some of the wire colors are different.  To top it off, the TCM I/O signal chart in the 2001 FSM shows the pinouts for three connectors.

If you have some of this stuff disconnected, you'll get a P0866 and/or P1698.

The TCM needs to be grounded, so ground pins B9 and B19 (brown/white wires) of the TCM.  If these aren't grounded I think it causes the OBDII port to not work.

One thing to do is to wire resistors in place of the solenoids.  If not you will get codes P0743, P0778, etc.  I would recommend 1000 ohm 10W or they will get pretty hot.  This is a lot more resistance than the solenoids but seems to work.  I got a terminal strip from McMaster.  I also kept the dropping resistor which was bolted to the passenger side strut tower.  That is wired into the circuit for some of these shift solenoids, see page WI-52 of the 2001 FSM supplement 6 cyl.

I wired a 330 ohm resistor in place of the ATF temp sensor.  This is in the middle of the normal range according to the FSM, and I've read other people have done this.  This resistor goes between the light green and yellow/white wires at the TCM.  The ATF temp light flashed when we still had the 2002 instrument panel connected, but never gave a trouble code.  I guess if you're doing a manual trans swap into an H6 car, just pull out that bulb or cut the wire to the idiot light.

If you're not going to have a Subaru automatic, you need to get around the inhibitor switch. 

The main thing you need to do is bypass the neutral/park switch for the starter wire.  The easiest thing to do is to splice the white/blue and white/green wires together near where they plug into the trans.  Once you take this all out of the car you'll see there's a lot of starter wiring going on, it goes through a harness plug that just has a jumper, and where it goes to that inhibitor switch it goes from being about 10 gauge to 20 gauge.  So I cut a lot of that out.

I cut the wires that are grounded in various gears, at the TCM these are B22 light green/black, B17 red/blue, B23 blue, A1 blue/black, A10 yellow/blue, B18 red/green, and B8 green.

We haven't had any codes in a while but just have it wired to think it's in drive all the time.  You do that by grounding the green wire to pin 8.  I actually have that and the neutral wire (light green/black pin 1) on a toggle switch so I can ground one or the other, but just leave it in drive.  It has stalled a couple of times, which I've read is a side effect of it thinking it's always in drive, but hasn't lately.  I have read that pin 8 B134 should be grounded in N, 5V in drive.  I think I just cut that wire and haven't had any codes since.  If I do flip my toggle switch to ground the neutral wire I do get a park/neutral code (P0851?).


One of the last wiring projects was the air conditioning.  The 99 system is pretty simple.  There is a wire for the AC compressor relay the ECU grounds.  The ECU also runs the radiator fans.  There is another wire that goes to the ECU that I assume tells it you have the AC switched on.  It goes through the temp sensor on the evaporator. The 2002 system is much more complicated. Four pages in the FSM versus one for the 99.  There are at least five wires going to the 2002 ECU related to AC.  Long story short I couldn't get it to ground the AC compressor relay. 

The 99 is pretty simple so it was fairly easy to hotwire the AC.  I plugged the connector from the 99 that goes to the compressor into the H6 compressor.  There is 12V going through the pressure switch and the thermal overload and then to the AC compressor relay.  If the pressure is too low (or maybe too high?) or the thermal overload is open, the relay won't have 12V.  The 2002 H6 compressor seems to have different thermal overload wiring than the 99, so I hotwired that.  Take the yellow and red/white wires at the compressor plug and splice them together.  The yellow/green wire going to the compressor energizes the clutch, it's the only one really needed.




I wired up a four pole switch to ground the AC compressor relay, fan relay, main fan relay 1, and sub fan relay 1.  This seems to throw a fan code on the ECU if the coolant temp starts to get hot, I assume when the ECU sees the fan relay is already grounded when it tries to turn them on it gets confused.




So now the AC works.  One good thing about this setup is that we could just unplug the compressor or compressor relay and turn the switch on to run the fans if it's running hot.  The biggest downside is that it doesn't turn off at full throttle.  That wouldn't be too hard to do, but I haven't bothered.


The next posts will cover the plumbing and mechanical issues.

Edited by pontoontodd
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Fuel lines/filter are the same.


I'd recommend using the H6 radiator as the radiator hoses will be much simpler that way.  But we already had a 2" thick core Mishimoto in the 99 that I really wanted to keep.  The H6 is definitely longer, maybe only an inch, but there is no way any Subaru fans are going to fit between the radiator and the engine.  Even if they did, I don't know where the air would go when it came out.  Piece of 2" square tubing pictured in between I was using to check for clearance.  I think the only reasonable solution is to put a pair of pusher fans on the front.




Exhaust from the H6 almost fit the 99, some modification will be required.  H6 exhaust hits the 99 trans crossmember on the driver's side.  Almost bolts up flush to the head, back end of the cats probably has to go up
about 1".  Exhaust will go to the driver's side anyhow, so I'll just tweak the stock system for now to fit.






We wanted to use the accessories on the H6 since the pulleys are different and it would make things much easier.


The high pressure (short) AC line from the 2002 and the low pressure (long) AC line from the 1999 seem to connect the 2002 compressor to the 1999 evaporator and condenser.


Power steering lines at the top of the crossmember thread right in.

Edited by pontoontodd

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For the most part, mechanically this swap is simple since it's Subaru into Subaru.


I had some difficulty removing the engine from the trans in the donor car.  I think they were corroded together and/or the bellhousing dowels and torque converter pilot were tight.  I used the hammer and chisel sparingly on the parting line and threaded some bolts into the engine and hammered on those.  Make sure you unbolt the torque converter, there is an access plug at the top of the block under the intake manifold.  It helps to put a jack under the front of the trans so the engine isn't holding it up while you're trying to separate them.


Make sure you have both bellhousing dowels in place in the engine or trans.


One thing I did before installing the H6 was to RTV that plastic cover for the torque converter bolts back in.  Also duct taped both sides of the flywheel shield, there were some slots in it.  May not last but it's a nice thought.  If you're not running in a lot of dust like we do, you can skip this.



Flywheel and clutch from the 99 bolt right up to the H6.

Transmission bolts up.

Starter works.

Engine mounts line up perfectly in the 99 crossmember.

Throttle cable hooks up, even has the right amount of throw.

Edited by pontoontodd

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any updates? I tried the links above, but they just come back here.


I need to update the wiring info a little when I get time.

The engine has been running great, no stalling or anything, makes decent power.

I do get some trouble codes related to evaporative pressure, fuel temp, and I did get a mixture lean code once.   I plan on getting it tuned sometime and I've heard they can keep some of those from coming up.

It does have a head gasket leak, the yard I got the last engine from has a 90 day warranty so I plan on replacing that soon.

I would definitely recommend doing a manual conversion in a six cylinder car rather than swapping one of these engines in a different car.

I think I just fixed the links.

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Went through this and my notes and I think all the information is here now, added a few things to the first post.

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