bw57409 Posted May 5, 2006 Share Posted May 5, 2006 My 98 Outback AWD has had the CEL on for the past month. The only symptom it has is irratic idleing and poor acceleration (may be a "get you home mode" from the ECU). However this only happens intermittently and when it does simply turning the engine off and restarting seem to clear the problem. I took it to my local garage and they carried out a diagnostic with a Snap-on Computer and the codes found were: P0500 Vehicle Speed Sensor, P1507 Idle Control System Malfunction and P1540 Speed Sensor Malfunction 2. The speedo is working ok and they found good signals from both speed sensors going into the ECU. In there words - "sensors and signals to TCM (transmission computer?) and ECM (ECU) test fine, signal from ECM drops out intermittently" Has any one heard of this type of fault? Could it be a faulty ECU or ECM if so how can this be determied prior to going to great expense on buying a new one. I am reluctant to go to a Subaru dealer from them to just start plugging in new parts to problem solve. Any advice would be appreciated. Quote Link to comment Share on other sites More sharing options...
ferret Posted May 5, 2006 Share Posted May 5, 2006 Manual (5sp) or Automatic (4EAT)? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted May 5, 2006 Share Posted May 5, 2006 with multiple codes showing i find it best to attack one at a time. in your case i'd look to solve the idle circuit malfunction problem first and go from there. it also might be a good idea to reset the ECU and see which codes appear immediately on the next start up. this would show the most emminent issues. not really sure on the speed sensor things, that's an odd ball of sorts, don't see very much of that. the vehicle speed sensors in older subaru's never cause issue, even when they cause the CEL to come on, but the newer ones could be completey different. that's why i mentioned that i'd look into the idle circuit more, it's more common and causes more issues on older subaru's when the VSS never does. but again...newer generations are completely different. you should be able to score a relatively cheap ($50) used ECU (engine computer) to swap in place and see if that alleviates any of the codes. he mentioned TCM - i'd guess he has an automatic. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted May 5, 2006 Share Posted May 5, 2006 1-828-724-1616 these guys have an ECU for $65 from a 1998 Impreza have you done any jump-starting or had any recent work done? I wouldn't expect an ECU to go bad for no reason. Quote Link to comment Share on other sites More sharing options...
ferret Posted May 5, 2006 Share Posted May 5, 2006 AHH, I see in your 1st post a TCM...so you have an Automatic. It could be as easy an a poor connection on the ECU ( signal wire goes to Instrument cluster then from that same pin the signal goes to the ECU, So since the speedo is working, the ECU connection may be making to make a good contact. I would try reseating the ECU connectors. This will set a P1507. 2nd, it may be the Neutral switch...Not only do they use this for activating the starter relay, but they also use it to tell the ECU when the car is in park or neutral ( no engine load ). This will set the P1507. The others, I would 1st check the accellerator cable, a pinched cable or one not returning to idle can cause P0500 or P1540. Quote Link to comment Share on other sites More sharing options...
bw57409 Posted May 5, 2006 Author Share Posted May 5, 2006 Yes its anautomatic. The shop that did the diagnostics had the ecu and tcu out of the car to check speed sensor pins going in to both computers. That will cover reseating the ECU conectors. Will have a look at the accelerator cable however car runs ok most of the time with the stall/poor idle fault happening infrequently sometimes one per journer sometime not at all. Where is the neutral switch and what can I do to look into the idle circuit? Quote Link to comment Share on other sites More sharing options...
nipper Posted May 6, 2006 Share Posted May 6, 2006 Neutral saftey switch is called an inhibitor swiatch and its located on the tranny. Usually multiple codes you look at them how do they relate to each other, you can usually figure out a chain. Here i dont even have a clue. The odds of BOTH vss sensors going bad at the same time are astronomical. i would check the harnesses to make sure the wires are ok. If one of your VSS were dead you would have no spedo and/or no awd, plus an angry flashing light someplace and weird shifting. I think you have a damaged harness. Also clear the codes, and with a reader on the codes shake the wiring harnesses and see if you get the code again. i wonder if your IAC (idle air control)is dirty. Thats fairly easy to clean. nipper Quote Link to comment Share on other sites More sharing options...
Jppare Posted December 1, 2013 Share Posted December 1, 2013 Hi Folks! I'm new here because i read about that trouble while i was searching on google to solve my problem.... Maybe someone can help me here. Since 2006 i hope that someone solved this problem and found what i was. Mine is a Legacy GT 98 Wagon with manual trans. My speedometer work fine but what i found with my obd2 reader is that the car receives weird signal causing VSS or Idle air control CEL. The ECU doesn't see any speed at all while my speedometer is working fine or seeing something but it's really erratic. I tested many wires with a ohmmeter and it seems to be ok. I found that my neutral swtich wasn't working at all, so i replaced the switch and did a test run. First run the car seemed to be repaired BUT! intermittent troubles still the worst troubles to find. The next day, i took it to go to the grocery store and BOOM CEL light come back on and the car stall at a red light. So put back the reader to see what is it and my trouble is back again. ECU receiving erratic signal or nothing. All the troubles on the car i linked to that no signal to ECU. on this pic i was rolling at 55mph constant....... that is weird! it dropped to Zero 2 seconds after that picture. Quote Link to comment Share on other sites More sharing options...
Gloyale Posted December 1, 2013 Share Posted December 1, 2013 Sending unit at the trans is bad/failing. Replace it. Quote Link to comment Share on other sites More sharing options...
Jppare Posted December 1, 2013 Share Posted December 1, 2013 What is the sending unit? I know that the speed is sent via the speed sensor to the cluster and then cluster is connverting signal to send it to ECU.... am i right or i'm missing something? Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted December 1, 2013 Share Posted December 1, 2013 Sensor sends a signal to the cluster. Cluster converts that signal and sends a different signal to the ECU. The clusters around 99 have problems with a ground trace on the circuit board. It makes the signal to the ECU erratic or none at all. Search for "99 speedometer fix" or something like that. There was a thread here just a few weeks ago about this with a link to a thread detailing the repair, with pics. Quote Link to comment Share on other sites More sharing options...
Jppare Posted December 3, 2013 Share Posted December 3, 2013 I finally found corroded connections on the ECU... Cleaned it but still have some troubles. I think the board had already too much damages to keep it... So now i am looking for someone that has an ECU for my legacy gt 98 manual trans engine is a 2.5l twincam Quote Link to comment Share on other sites More sharing options...
Colinmcrea01 Posted February 8, 2022 Share Posted February 8, 2022 Got a 97 Subaru legacy 2.2 auto. Lifted it 1 inch. Running 215 70r15s on it now. Much bigger then stock. Check engine light comes on 2 miles from house every time I drive it. Stalls at some stop signs and sometimes seems it goes into limp mode until I turn off and back on? Being it's an automatic would that cause the speed sensor to malfunction at low speed. Just wondering if I should go back to a smaller size tire.... Quote Link to comment Share on other sites More sharing options...
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