987687 Posted June 29, 2010 Share Posted June 29, 2010 I'm having a strange issue with the speed censor on my 1996 Legacy L. 5speed. 114k miles, but it's been doing it for a good long time. Here's the facts. The speedo on the dash always reads correctly. I have a scangauge2 installed and one of the options set to the speed the ECU sees. And it doesn't always match the speedo gauge. It's often a good deal less, or sometimes just goes to zero in which case after a few miles/shifts I'll get a P0500. USUALLY turning the car off and on again will make it act normally, but not always. And just recently it's developed another related issue. Sometimes when I push in the clutch or shift to neutral the engine will completely stall. And it ONLY happens when the ECU is getting zero for a speed signal (but the gauge is still working perfectly...). But it doesn't always happen, just every now and again. And it isn't clutch drag or anything like that because it's adjusted correctly and happens both when moving and stopped. And one more interesting thing. Last year it had a weird issue that it's now stopped. Which I don't get... But it was this. When the transmission had warmed up after a few miles of driving the speed would jump around (both on the scangauge and on the dash) when I drove under 20mph, over 20 it was fine. It would only do this when warm though, and if it was the middle of winter it would take about 20 miles to actually warm up enough to act up. I don't know if that's correlated at all. But maybe. One other thing is that the gauge cluster does NOT have a speedometer cable going into it, only wiring harness plugs. Link to comment Share on other sites More sharing options...
Legacy777 Posted June 29, 2010 Share Posted June 29, 2010 I'm pretty sure the 96 had the speed sensor on the transmission. If that is the case, I would probably start there. If you can find a used one, or if they're not much money, I'd probably replace your existing one. If it's not the sensor, it could be the wiring from the sensor to the ECU. Link to comment Share on other sites More sharing options...
johnceggleston Posted June 29, 2010 Share Posted June 29, 2010 from what i have learned swapping out a trans and a speedo, the data moves from the vss directly to the speedo, and then from there to the ecu. actually i do not know it moves from there to the ecu, but it gets to the ecu some how and i have seen no indication that is goes there first. especially considereng that the 94s had a speedo cable from the trans to the speedo. no way did the speed data go to the ecu before the speedo in 94. so trouble with the ecu speed is probably the speedo. the speedo jumping around, i think, is usually the vss but it could be either. re: the ecu speed, maybe the speedo outputs to the ecu are dirty. speedos and instrument clusters in general are a dime a dozen any legacy 95 - 98 will work. avoid the GT (and maybe LSi) if you can, that swap is a headache. outback will probably work, but lego L or LS is a sure thing. Link to comment Share on other sites More sharing options...
Cougar Posted June 29, 2010 Share Posted June 29, 2010 (edited) I agree with Legacy 777. The code states there is a problem with the sensor. It could be just a wire connection problem, as he also said, so that should be checked first before replacing the sensor. Going from what you said about the other symptom you had I think it kind of points to just a connection problem to the sensor. Edited June 29, 2010 by Cougar Link to comment Share on other sites More sharing options...
987687 Posted June 29, 2010 Author Share Posted June 29, 2010 It has a censor on the transmission where older transmissions have a cable. And the censor has 2 wires coming off it going into the wiring harness. So that supplies the speedo and the ECU. I don't get why one would work and why the other wouldn't. Seems like an ECU thing to me, maybe. Link to comment Share on other sites More sharing options...
Cougar Posted June 29, 2010 Share Posted June 29, 2010 What makes you think the ECU is bad? It is telling you there is a problem with that sensor or wiring to it. Your Scangauge is telling you the same story. When the signal gets bad enough the ECU shuts down the engine. Hopefully the Scangauge connection to the sensor isn't causing this trouble. You may want to isolate that connection to see what happens. Link to comment Share on other sites More sharing options...
987687 Posted June 30, 2010 Author Share Posted June 30, 2010 What makes you think the ECU is bad? It is telling you there is a problem with that sensor or wiring to it. Your Scangauge is telling you the same story. When the signal gets bad enough the ECU shuts down the engine. Hopefully the Scangauge connection to the sensor isn't causing this trouble. You may want to isolate that connection to see what happens. What do you mean the scangauge connection to the sensor? I don't see how it could be causing an issue because it's just reading out of the obd2 port. Seeing as only 2 wires come out of the sensor into the harness, and the speedo works right I can't see why the sensor would be the issue. But assuming it is, is there any way to test the sensor besides throwing a different one in there? It doesn't look very fun to get out. It looks like it has the same plastic nut thing the EA transmissions use. Those aren't fun... Link to comment Share on other sites More sharing options...
Cougar Posted June 30, 2010 Share Posted June 30, 2010 (edited) What do you mean the scangauge connection to the sensor? I don't see how it could be causing an issue because it's just reading out of the obd2 port.Seeing as only 2 wires come out of the sensor into the harness, and the speedo works right I can't see why the sensor would be the issue. But assuming it is, is there any way to test the sensor besides throwing a different one in there? Ok. Thanks for the heads-up on the connection. I was mixed up on a couple of things and see your point now. I think there are two speed sensors used on your car but I'm not positive on that. If there are two then the trouble may be with the one going to the ECU. Again, the wiring to the sensor should be checked first before replacing the sensor. I looked at some data for a 95 model and it shows two speed sensors are used in it. One is for the speedo and the other for the ECU. Edited June 30, 2010 by Cougar Link to comment Share on other sites More sharing options...
johnceggleston Posted June 30, 2010 Share Posted June 30, 2010 I looked at some data for a 95 model and it shows two speed sensors are used in it. One is for the speedo and the other for the ECU. auto trans - my understanding is that 90 - 99, AWD have 2 and Fwd have only one. the ecu will uses th front one for info unless it dies and then it will use the rear. (i don't know how.) usually the rear is used to control the power transfer to the rear wheels. phase 2 auto trans (99? up) added speed sensors to the trans and wires to the harness which makes it difficult to swap phase 1 and phase 2 trans. there is also a limp home mode which i would think would kick in if the ecu wasn't getting any data at all, but i don't really know. generally speaking, if the car runs alright, i would suspect the front seed sensor or the speedo. but checking the wiring is free so do that first. i just do not see how the speedo is reading correctly? and the ecu has '0' unless it is a connection problem between the two. either the output from the speedo or an actual wire connection. i guess it could be the ecu, but that is pretty rare, i think. Link to comment Share on other sites More sharing options...
987687 Posted June 30, 2010 Author Share Posted June 30, 2010 Again, it isn't necessarily the output from the speedo. I've run the car with no gauge cluster at all, actually. Mine died so I was getting a used one and rolling the mileage back. But for a day I had none in and just used the scangauge. And at that point it gave the correct speed. I've never head of the manual trans having 2 speed censor hook ups, but I guess I can check. Link to comment Share on other sites More sharing options...
johnceggleston Posted June 30, 2010 Share Posted June 30, 2010 (edited) ooops! Edited June 30, 2010 by johnceggleston Link to comment Share on other sites More sharing options...
Cougar Posted June 30, 2010 Share Posted June 30, 2010 The Cat here must be on too much catnip for I now realize that we are talking about a manual transmission and not a AT and was clearly stated in the beginning. Another foepaw on my part. Sorry. I have to agree with you 987687, I don't think there is a second sensor for a MT. The Cat is going back to the cave and ponder this trouble because that is all I've got for now. Link to comment Share on other sites More sharing options...
johnceggleston Posted June 30, 2010 Share Posted June 30, 2010 The Cat here must be on too much catnip for I now realize that we are talking about a manual transmission and not a AT ooops!! Link to comment Share on other sites More sharing options...
987687 Posted June 30, 2010 Author Share Posted June 30, 2010 Glad we're all on the same page now... I was confused as to what you were all talking about... I understand why you all assumed auto though, the autos are much more prone to this type of vss issue seeing as they have 2, AND most of these cars are autos. I have never read and can't find anything about this sort of issue on a manual that doesn't have a cable. Obviously if it has the cable it's perfectly obvious what the cause is if the gauge reads correct and the ECU is incorrect, the vss in the gauge is off... but this? dunno.... It's getting really annoying though having my engine shut off. Today I was going through an intersection. I shifted to neutral because it's a downhill so I was just gonna coast through, but then it stalled. Scary!!! Link to comment Share on other sites More sharing options...
Cougar Posted July 1, 2010 Share Posted July 1, 2010 I have to assume that the one sensor is tied to both the speedo and the ECU on seperate legs and the circuit leg for the ECU has a problem. Do you know which pins of the ECU are used for the speed sensor? If you do then you need to follow them and check for any trouble on them. Link to comment Share on other sites More sharing options...
987687 Posted July 1, 2010 Author Share Posted July 1, 2010 I guess I could find the pin on the eco, fix my oscilloscope (which I should do anyway). Then I'd have to wait for it to act up again so I could start tracing stuff and finding out what's wrong ... Link to comment Share on other sites More sharing options...
Cougar Posted July 1, 2010 Share Posted July 1, 2010 You may not need a scope to find the trouble. If the trouble is just due to a faulty wire connection an ohmmeter should be sufficient I would think. Link to comment Share on other sites More sharing options...
edrach Posted July 11, 2010 Share Posted July 11, 2010 (edited) The Cat here must be on too much catnip for I now realize that we are talking about a manual transmission and not a AT and was clearly stated in the beginning. Another foepaw on my part. Sorry. I have to agree with you 987687, I don't think there is a second sensor for a MT. The Cat is going back to the cave and ponder this trouble because that is all I've got for now. I have a '97 Impreza with a cable driven odo/speedo. The VSS is shown in the FSM and is built into the Speedometer itself. From the wiring diagram one side of the VSS is tied to ground and the other feeds to the ECU at terminal 83. Judging from the diagnostic info in the FSM, the VSS generates 4 pulses per cable revolution. My susupicion is that the internal VSS is a reed switch dropping terminal 83 of the ECU to ground 4 times per cable revolution. I'm not sure how this helps. If needed, I can scan the appropriate pages of the FSM and send them out to you. Edited July 11, 2010 by edrach Link to comment Share on other sites More sharing options...
987687 Posted July 11, 2010 Author Share Posted July 11, 2010 Thanks, it does help because it tells me how the VSS works. It's probably the same for the transmission mounted one like on my car. It's only happened once since last time I posted. It was reading a low speed on the scagauge, then dropped to zero. But as I was going along I turned the key off and on again and it was working fine right after that. The fact that it works fine after turning the car off and on makes it rather difficult to diagnose :-\ Link to comment Share on other sites More sharing options...
edrach Posted July 11, 2010 Share Posted July 11, 2010 Thanks, it does help because it tells me how the VSS works. It's probably the same for the transmission mounted one like on my car. It's only happened once since last time I posted. It was reading a low speed on the scagauge, then dropped to zero. But as I was going along I turned the key off and on again and it was working fine right after that.The fact that it works fine after turning the car off and on makes it rather difficult to diagnose :-\ Yes, intermittants are always tough. I use a scanguage II regularly in my car and never had any problems with it other than it sometimes forgets that it's in a subaru and I have to reset that function. I run undersized tires and appreciate the fact I can adjust the mph readout when necessary. I've been looking into the VSS since I'm looking for a source of reliable odometer impulses for a rally computer I'm installing. I'll let you know how that works for me. Back to your issue: The VSS sends pulses to the ECU which in turn sends the information to your OBDII connector and then to the scanguage. Part of the wiring diagram shows another connection between the VSS and pin 83. It is apparently the connector on the rear of the instrument cluster from what I've been able to tell. If your speedo AND scanguage both fail at the same time, I'd expect that connection to be the intermittant one in the chain. Removing the instrument cluster and reseating all the connectors might resolve your problem. Other than that, the VSS itself might be at fault in which case the only solution is to replace the speedometer/odometer portion itself since I believe the VSS resides inside that unit. The last thing I would suspect would be the ECU although that would be the easiest item to replace. Your year of Subaru is getting pretty common at the boneyards and finding a used replacement shouldn't be too pricey. I think the Seattle area pull a part yards charge $25 for an ECU. Link to comment Share on other sites More sharing options...
987687 Posted July 11, 2010 Author Share Posted July 11, 2010 As I've said in previous posts, my instrument cluster doesn't have anything to do with the signal the ECU gets. My VSS is actually on the transmission, there is no cable. I've driven the car with no instrument cluster and at that time my scangauge2 showed the correct speed. I was replacing the instrument cluster because it stopped working due my my alternator spiking really high. And since then my electrical system has been acting stupid, so that probably has to do with it. Link to comment Share on other sites More sharing options...
edrach Posted July 11, 2010 Share Posted July 11, 2010 (edited) As I've said in previous posts, my instrument cluster doesn't have anything to do with the signal the ECU gets. My VSS is actually on the transmission, there is no cable. I've driven the car with no instrument cluster and at that time my scangauge2 showed the correct speed. I was replacing the instrument cluster because it stopped working due my my alternator spiking really high. And since then my electrical system has been acting stupid, so that probably has to do with it.I'm sorry, I missed the part about your not have a cable driven speedo. My bad. The alternator spiking high is significant. My thoughts go back to the VSS on the transmission or the ECU in that case. Someone must have an FSM for your model to verify the wiring between the VSS and ECU (and any connectors in between). I should think that would narrow down where to be looking for an intermittant connection. Edited July 11, 2010 by edrach Link to comment Share on other sites More sharing options...
Cougar Posted July 11, 2010 Share Posted July 11, 2010 Since resetting the power makes it work again then check for a power connection problem. Link to comment Share on other sites More sharing options...
987687 Posted July 11, 2010 Author Share Posted July 11, 2010 Since resetting the power makes it work again then check for a power connection problem. Power to what? the ECU? Link to comment Share on other sites More sharing options...
Cougar Posted July 11, 2010 Share Posted July 11, 2010 No, the VSS sensor. Link to comment Share on other sites More sharing options...
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