CEL Concerning VSS: I'm Confused

[the_bard]

Background: '97 OBW. Manual transmission. Swapped in a new clutch & kit last weekend. Changed the transmission fluid last Wednesday. No problems immediately thereafter. My father's fighting cancer (and a gall bladder infection, now), so I had the work done in preparation for using it to travel to see him. It's a good three hour trip, nearly all highway.

 

Symptom: Halfway back to Albany last night, the CEL came on steady. No other indications of problems. Speedometer was steady. Cruise control had no issue. Engine continued running fine. I stopped at the next "civilized" exit, and found an Advanced Auto Parts located just off the exit. I pulled the codes: P0500 and P1540.

 

Confusion: I haven't had time to actually take a look at the problem, other than reseating the connection to (the/one of the) VSS on the passenger side of the tranny. I crawled into bed last night at home, then drove my wife and I back down to the hospital in Elmira this morning. Not that having the car in front of me would help... I'd probably still be confused .

 

Now, from what I understand of my research:

 

1. I've only got one VSS. Manual tranny's have one VSS, auto's have two (the TCM refers to both when controlling the AWD).
   
2. I'll check the manufacture date, but I believe a '97 OBW shouldn't have a speedometer cable... it should be run off the VSS.
   
3. 1 + 2 means the speedometer should have quit if the VSS quit.
   
4. Because the speedometer didn't quit, the VSS might be intermittently failing, or there's a wiring issue.
   

So I think my best route now would be to simply clear the codes, and see if it reoccurs. Might be a good idea to waterproof that VSS connection, too, since it might've picked up moisture off the road (it was foggy last night with light rain).

 

If those codes reappear, then I should swap the VSS.

 

Anyone want to poke holes in my boat?

[lmdew]

Sounds like a good plan. Yes you should only have 1 VSS on the manual trans.

[hankosolder2]

Well, I was just googling your codes and came across this link.

 

Did you disturb any grounds during the clutch work?

 

http://wiki.answers.com/Q/What_are_codes_P0500_P1507_and_P1540_on_a_1997_Subaru_Legacy_and_how_do_you_repair_the_vehicle

 

 

I agree with your logic- if the speedo and cruise are working, it doesn't sound like a bad VSS (at least on a manual trans vehicle.) I suppose there's always the remote possibility of it being a threshold problem---i.e. the VSS signal is supposed to pulse from 5 to 0 volts... let's say that the sensor has failed in an unusual way or there's an open ground and the signal swing is abnormal. The speedo and cruise might be more tolerant of out of spec voltage swing than the engine control computer. It's a long shot, but possible.

 

Sorry to hear about the situation with your Dad's health.

 

Nathan

[lmdew]

There's a ground that should go from the firewall pitch stopper to the trans, its about an 1/8" dia wire. Good size.

[the_bard]

Thanks for the sympathy, Nathan. It's one of those facts of life, though... almost as bad as taxes.

 

I'll check the ground when I get back home. i should have time Tuesday night or Wednesday morning to play with it a bit. That tranny got yanked around enough while we were trying to line the engine up with it. I wouldn't be surprised to see if we damaged that ground wire or its connection enough to allow the wet weather to wreak havoc. Come to think of it, last night was the first occurrence of wet weather since the swap, so I wouldn't be the least bit surprised.

Edited November 15, 2009 by the_bard

[Fairtax4me]

Voltage issue sounds likely. Probe the connector at the VSS and see if it is getting 5V from the ECU.

[the_bard]

I took a look at the grounding wire that leads from the tranny to the pitch stopper. The bottom bolt was *tight*... too tight for me to break loose easily, without having to take something else off to get the room to do so.

 

I did break loose the top bolt. It had a bit of corrosion on it... I cleaned it using a small screwdriver and wire brush.

 

Took Serenity around for a twenty minute drive, and all seems well. Time will tell.