inspired by the people on club sub and reading the suby docs i figured DIY this weekend and share the notes before forgetting.
mine is the face-lift 07 auto trans H6 3.0R with engine push start button. not all loom wiring is pre made for these model years. The purpose here is to complete the cruise control system by installing cruise buttons and parts to supply a brake switch signal to ECU pin B20. This is my write up, don’t do anything to stuff up your vehicle or anyone's safety and if you are not sure stop. steps are in sequence each dependent on the previous.
1. Have the correct service manual for your vehicle @ http://jdmfsm.info/Auto/Japan/Subaru/Legacy_Outback/ or https://techinfo.subaru.com. Print and read the relevant pages in the subaru service manual because there is important information and safety info in the 5,000+ page service manual that is not detailed here.
2. Most of these steps required the battery to be disconnected.
3. Check cruise and set lights are available on your dashboard, even if they are never lit. We only noticed ours when the sun was right behind us.
4. Check cruise is supported by the ECU. I used FreeSSM with a cheap vagcom cable and the engine diagnostics page shows integrated cruise control on the left hand side of the window. Not all models support cruise apparently higher spec models are more likely to
5. Check you have a 2 pin brake light switch and there is not a 4 pin loom plug tucked away in the loom near your brake light switch. if there is you are lucky and subaru have saved you a heap of time, just replace the switch with a 4 pin and ignore all of the new wiring steps.
6. Use the service manual to identify and check the ECU under the front passenger foot well carpet that ;
1. C25 (clutch pedal pin) is wired green yellow and tied 12v with ignition on (for auto transmission models), subaru included this wiring for us
2. note/ you could probably easily pick up the ignition 12v from elsewhere if you wanted to but i wanted to test C25 was working per the wiring diagram.
3. B20 (brake switch) is not wired. Subaru didn’t include this for us as they did for some previous model years.
7. Check which cruise controls are required. Similar legacy/outbacks to mine have steering wheel cruise control
8. Go to the wreckers and pick up;
1. Steering wheel cruise control buttons
2. 4 pin stop light & brake switch
3. 4 pin stop light & brake loom connector with some wiring
4. ECU plug with 5cm+ wires attached (computer under passenger footwell). This is so we can take a pin out to use on B20
9. not familiar with these components? practise removing ECU pins and also the connectors from the brake switch loom connector as this skills will be required later on. I didn't this before so asked for help @ https://mechanics.stackexchange.com/questions/48623/how-to-remove-pin-from-subaru-ecu-plug
10. Install steering wheel buttons which required removing the wheel to unscrew the buttons panels from the rear side. My SW buttons were stereo controls on the left and a blank plate on the right. Put it back together now the cruise dash light is shown during lamp test when the ignition is turned on. The set button on the steering wheel won’t do anything. May get a DTC whilst driving when the computer realises the other circuits are not ready.
11. now need to wire the normally closed contact on the 4 pin brake switch to feed ECU pin B20. I took the ignition power from C25 (spliced a couple inches back from the ECU plug) up behind the foot well, above the stereo and over to the brake switch location. The return came back along the same path to the ecu’s pin B20. This was time consuming because removed most of the front trim panels to follow existing loom paths. Used solder and heat shrink on all splices/joins and a PPS cable sleeve. Don’t work on ECU cables with their plugs connected to the brain. At first I couldn’t get the new ecu pin into B20 but gently did it to click in with the crimped side facing downward.
12. Replace 2 pin brake switch loom connector with the 4 pin. Used a small flat jewelers screwdriver to pop out the white/blue and brown/white wires from the new 4 pin loom connector as loom already had those. Popped out same colour wires from the 2 pin and moved them over to the four pin. Connected in the new cables from previous step. See pix above from @sobanoodle that yellow & green yellow wires are the new ones. Your green (or equivalent) goes from pin 1 on the connector to ECU B20 and your green/yellow from pin 4 on the connector to the ECU C25 splice.
13. Replace 2 pin brake switch with the 4 pin brake switch using a 12 mm spanner and check it is in the correct position. I used a multi meter to check the contacts changed state when the brake pedal was depressed even slightly (had to adjust the switch position, don't wanna be rear ended with no brake lights). It was good to test from the ECU side as well to check the new circuit is working end to end.
14. Put back enough of the panels and connectors to have the car driveable and test the engine starts with no warning lights.
15. didn’t do anything else to enable cruise because the computer detected all of the signals were in place. it automatically enabled and made the cruise available
16. go drive to test the new cruise control, it worked - the cruise function and dash lights operate nicely
If I did this over would probably use another source of ignition 12V rather than have to splice the C25 wire. anyways done now and uses same circuit, fuses and pins described in the service manual for the factory cruise.