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scottmcphee

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    www.autowindow.com
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    06 Legacy 2.5i Wagon MT
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    Electronics for cars!

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  1. If your throttle body was like mine, it was riveted shut. I drilled out the rivets to clean what was inside. This sensor uses hall-effect elements that are essentially hermetically sealed. So there was nothing to clean inside the sensor cover on this throttle body because there is no wear item. No dirt was in there to speak of. The only thing to clean out are metal filings that you put in there when drilling off the cover. And of course, there's a matter of putting the cover back on. I used several small bolts and a dab of glue on each nut after tightening down to prevent them backing off. These additional rough idle symptoms could be many things. You need to get codes and/or operating parameters off the car to see what is causing the roughness. You can do simple things, like unplug the MAF sensor. This will throw codes of course, but also causes car not to rely on MAF so it enriches the mix and you can drive the car, using more fuel than you should... but it forces Open Loop - and the ECU ignores many inputs from emissions sensors. It can change your idle and responsiveness to pedal. It can change the starting (cranking) behavior. When you drive this way, maybe there is no "dip" or worn spot on the pedal ... maybe there's smooth revs up through that area. When you're done experiment, connect your MAF again. Clear codes. Are you getting front O2 / AFR codes? Car depends very much on a good front sensor for good running.. if you haven't changed that in 8 years or so, maybe it's due even if it is not coding. Rear O2 codes? Is the cat getting plugged? The car can do limp mode for different reasons, not always / only the p2138 code. But if you pulled that code, then start with the pedal... work your way back to the ECU. Follow the diagnostic for tracing values on the pedal wires..
  2. Other update: I got a spare ECU off ebay for about $100 and I reflashed it with my stock ROM from my original ECU. When you do an ECU swap on 2006 Legacy the car is undriveable until you get the keys re-registered to the car by a dealer. So I would suggest doing the swap AT THE DEALER rather than having to tow the car in... But I circumvented all that by moving over the little 8 pin EEPROM from my original ECU to the replacement ECU, by unsoldering / soldering it in place. This carries the key codes over to the new ECU so re-registering keys is unnecessary if you do this. So what did all this get me? A working car again. Been driving for days, and the random p2138 and p0139 codes have not come up since. It was a bad ECU in my case causing the p2138. This is "worst case" scenario for this code. And would be the last resort looked at by dealer. Man what a goose chase! That would have been an expensive process if I let a mechanic / dealer follow the diagnostics to arrive at the same conclusion and dealer finally having to drop a new ECU in. They most certainly would have put a new pedal in first too. Probably would have added up to the value of the car.
  3. Update on the Saga programming DTC codes off using ECUflash and Tactrix 2.0 cable is possible, so I tried programming off p2138 code and reflashed the ECU. The programming took hold and did what it said, and the car was driving, and boom! Car went into limp mode after a short while... and (as promised) with the p2138 code programmed off, the "check engine" light did not light up blinking. However, the cruise control light still came on solid, and the car still went into limp mode. In other words, the fault of a p2138 when detected by ECU is serious enough to still make the car go into limp mode, whether or not the DTC has been programmed off.
  4. Wow, still didn't solve the P2138 with all the redundant connections at ECU. After a couple days of driving like this, p2138 comes up and I'm in limp mode, again. I think the ECU itself is glitching. So I'm getting a "new" (to me) ECU. UPDATE July 2016: the reason the p2138 with this arrangement WAS BECAUSE the ECU was flakey. Replacement of ECU has solved this issue. The ECU has shown a voltage problem for an O2 sensor coming in on the same plug / area on the circuit board. The O2 sensor is good and is producing voltage swings between 0 and 1 volt, as it should. Sometimes the ECU reports (via OBD scan tool) the same voltages I'm measuring on the ECU pin at the motherboard (using a volt meter)... sometimes it doesn't, it might report a half volt higher. Or just report a constant 0.6v ... as I'm watching the REAL O2 sensor swing anywhere between 0-1v. That's a real stubborn ECU not showing the voltages that I can see going into it! My thinking is, if voltage referencing is somewhat baked on the ECU for the O2 sensor. It could be baked for one or both pedal sensors too. While the ECU is shipping... I tried programming off the DTC p2138 code using an OBD connected ECU flash reprogramming tool (Tactrix/ECUflash), and going for a drive. Car will start and drive with this DTC programmed off, but when the car trips on a p2138 fault (D/E voltage discrepancy) is still goes into limp mode - only the "check engine" light remains OFF but the "cruise control" light still comes on while car is limping along. I was kind of hoping the ECU would "ignore the fault" but it won't. Too safety oriented.
  5. Here's what I ended up doing, in addition to cleaning all the pins thoroughly... Found some spare (empty / vacant) pin positions on plugs at ECU, and added female pins to the plugs in those positions and brought all the pedal sensor lines from inside the ECU out on these additional pins, leaving the original pins for this purpose intact as well. Right near the ECU I made jumpers from my new pin wires to the matching original wires for these sensors. Each black dot is a solder joint and taped. Notice I soldered the two grounds together outside the ECU, as they are also connected in common inside the ECU (taken off the same ground plane). So it's OK to bridge the grounds outside the ECU as well. This makes ground super redundant. But I kept the +5 supplies apart and matched to the corresponding sensor signal they support. So now, all the connections at the ECU are redundant for each wire going to/from the pedal. In the case of ground, it's 3-way redundant. All the rest are 2-way. This required some surgery inside the ECU, which involved soldering small wires, and snipping connector pins to disconnect them from the board. I was able to find enough of the larger pin 040 vacancies on the "top" row of the huge connector, which made it easier to work inside the ECU.
  6. I had bad luck when linking the +5v lines together, so I don't recommend that. It must not be direct connection to +5 but rather a controlled and/or monitored supply of voltage for each sensor. When I bridged the +5's, using the gas pedal consistently started throwing error codes when pressed more than half way down. So I removed the jumper. Even after that, the pedal started throwing voltage too high errors. I measured, and yes the voltage input range of each sensor was now extending up to nearly 5 whereas before they only got as far as about 3.5v when the pedal was floored. I thought I had buggered the ECU. I broke into a cold sweat. But miraculously the ECU righted itself and the car is driveable again with no error codes (at the moment) from the pedal. I think somehow the ECU is self calibrating or re-learning pedal mapping and range of input it is receiving from pedal sensors. Might have to do with drive cycles, and/or removal of power of the ECU. Lesson: don't bridge the +5 side. Bridging the ground side is fine though, it adds an element of redundancy. I am learning more than I want to about the drive by wire system of this car.
  7. At a minimum, for the drive by wire critical system, it would have made good sense to use a pair of pins through each connector to carry the signals instead of just one path. Because that's most unreliable point in the circuits.
  8. This was my theory: If they jumpered +5 and Gnd anywhere between the connectors, then one failing connection of +5v or one failing connection of Gnd, at the ECU would have no effect on the system. You'd still get two good signals back A and B. In fact, you could have one failing +5v pin AND one failing Gnd pin / connection at the ECU side at the same time, and still no negative effect. If Subaru designed the inside of the pedal sensor to have the jumpers across the +5v and Gnd internally, then you could have a failing connection of either +5 or Gnd at the pedal connector as well, and survive with no ill effect. (The ECU side internally on the board, does connect grounds together. I think it also connects the+5v together). There are good reasons for keeping things apart and not jumpering the powers. Supposing one power source fails, it brings down both, but this argument evaporates if the ECU is tapping off a shared power rail for +5 and Gnd, which I'm pretty sure it does. The only remaining argument would be for rouge voltage being introduced on the wiring on its run to sensor. That would knock both inputs off their mark, if powers were jumpered together. **** UPDATE **** The theory on +5 bridging has proven wrong!
  9. It strikes me odd that Subaru wouldn't take advantage of the redundancy of having 2 powers and 2 grounds going to the same sensor connector. And do this, from the factory: ***UPDATE*** Don't bridge the +5 sides together. Read down in this thread as to why I learned this the hard way.
  10. When running with one sensor dummied out... Car eventually threw a p2138 (A doesn't agree with B) The value read on input A is too far out of whack with what is read on input B. The only way that can happen is a problem at the ECU / or its connector. Or the reliability of the jumper. UPDATE July 2016: the reason the p2138 with this arrangement WAS BECAUSE the ECU was flakey. Replacement of ECU has solved this issue. As shown, with one dummied out, the connector for input A or input B at ECU is probably flaky. (Because the jumper makes the voltage on the wires for A and B identical for that length, the only place of discrepancy can be the ECU end and its connector.) Or perhaps the 5v or Gnd pins for sensor A are flaky, and the car is throwing p2138 when either/both of the inputs "drop to zero" momentarily, as would be the case if voltage does not have a complete circuit flowing through the still-connected single sensor. But the car has 4 other codes for values out of range of these sensors... more likely A or B inputs are flaky.
  11. Some things I know about the pedal and sensors and wiring.. This is a stock pedal and ECU, in my car wired like this.
  12. So, need to tighten / clean / replace the female pins inside the B plug. How to get this plug apart, pins out? ?? anyone I've asked in a thread over here: http://legacygt.com/forums/showthread.php/getting-pins-out-ecm-ecu-plugs-252651.html I have answered my own question of getting pins out... here: http://legacygt.com/forums/showthread.php/getting-pins-out-ecm-ecu-plugs-252651.html
  13. It is a jinx upon oneself to ever mention a code going away. p2138 came back, and it's "buddy error" p0139 within a day of each other and the day following me putting the ECM back into its proper fixed position to the floorboard, covered by its metal shield. These two error codes are from completely unrelated systems in the car. However, the sensors for each code share pins on the same ECM "B" plug. So these errors are "roommates" at the ECM. I had driven several days with no issues of P0139 or P2138. Happy with those results, thinking the cleaning of the pedal sensor made all the difference and cleaning the O2 sensor pins helped, I decided to mount the ECM properly again, bolting it down, covering it. Did that then Bam! Both issues p0139 first hit the following day and P2138 the next. Worthy of note: I did get the p2138 first thing in the morning after car had been sitting for a couple days, and garage at around 15 degrees C. Car cabin was soaked at this temp. Metal shrinks when cold. Heat expands it. And my wife a couple weeks ago, also got the p2138 after pulling out of the garage in morning, when cold. (The ECM was mounted at that time too.) Hmm... I have been going slowly between steps with lots of drive cycles before doing too much at a time... trying to isolate the problem, to KNOW what action is causing the issues. That is why I was driving for a week with the ECM exposed (metal cover plate off). I noticed when mounting the ECM properly it required "stuffing" the harness into its place behind the kick plate. You cannot mount the plate without putting pressure on the harness where plugs go into the ECM. There is a foam structure back there with a channel allowance for harness routing, but the harness is too bulky (foam allowance too small). As a result, you must squash the harness into the allowable space, and even after doing that, the metal cover/kick plate presses onto the bulging harness as you tighten its 4 bolts down. Squishing the harness .. putting the most pressure right where ECM plugs go in, and approximately connector B. Plus I can appreciate passenger feet on the floorboards over time pressing down on the carpet there, putting pressure on the plate which is essentially in direct contact with the harness, plug B, and ECM. This plus temperature flux in the cabin over seasons.. has softened the contacts of pins in this harness, I'm pretty sure. We are seeing temperature shifts of nearly 20 degrees C on a daily basis. These ECM plug/pins have probably gotten a bit relaxed in their clamping power and are going intermittent. Taking the cover plate off the ECM allows the harness to be "expanded" (pushed) out by the foam. When this happens, it probably shifts the pins inside the plugs and they find slightly different contact points.
  14. I'm just at the point of having a good pedal again that (knock on wood) hasn't thrown a p2138 code for days... A new record! Scared of possibly wrecking a good thing by putting a greasy film on the carbon traces. Did you know the wiper of the pedal sensors is not your typical looking thing you'd find on a regular pot? The wiper has tiny metal fingers bent and positioned to look like scrapers that sweep the trace. Just to see them you'd think they'd chew their way through that material in no time scraping back and forth... but it must be very hard carbon material. Put another way, they seem very capable of cleaning the surface they want to run on! These wipers are not like the back side of a dimpled spoon shape rubbing back and forth like a saucer floating over water. I do worry that putting dielectric grease film on those carbon traces might clog up the "fingernails" of these wipers, interfering with the electrical contact they need to make. For now, no grease. I'll see if oxide becomes a problem.
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