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Car Forum / Nissan / Nissan Cars / May 20071994 sentra speedometer / odometer quit
Hello. My GF has a 1994 Sentra, 4dr, automatic, 1.6litre engine. While driving the other day, the speedometer simply quit. Shortly after that, the check engine light came on. Otherwise, the car still runs perfectly. Still shifts perfectly and gets good gas milage. I'm no mechanic, but I like to try and figure stuff out if I can. My first thought was a sensor. I've read that there is a vehicle speed sensor on the transaxle (the part between the two axles feeding the two front wheels?) I read that this thing should put out 0.5 volts AC while spun, so I tried to locate it and take it out. I think I have located it (round, about 1 inch in diameter, near the back of the engine compartment on the driver's side, down low, below what might be a fuel filter ...) but I wasn't sure how to get it out. Any tips? Is it a screwed connection, or just brute force? What are the chances that the problem is actually in the dash? Local dealer says $330 just for the part! thanks for any help, Chicobiker The speed sensor in the trans rarely goes bad. You can test it without removal. Previous threads have repeated that the speedo is the culprit. One of the IC's in it goes bad, but the IC itself is not available in single or small quantities. Go find a used one in the junkyard, instead of the overpriced one at the dealer. -SP > Hello. > [quoted text clipped - 18 lines] > thanks for any help, > Chicobiker I have this problem in my Maxima while back. The problem was NOT the speedo but the crankshaft position sensor. This is an easy part to get to (one screw) and I'd check this and its cabling first. Replacing speedo is a lot harder and may cause other electrical problems. Hmmmm! Do tell- How is the crank sensor connected to the speedo??? I realize strange wiring is always being invented, but this doesn't make sense. -SP > I have this problem in my Maxima while back. The problem was NOT the speedo > but the crankshaft position sensor. This is an easy part to get to (one > screw) and I'd check this and its cabling first. Replacing speedo is a lot > harder and may cause other electrical problems. > Hmmmm! Do tell- How is the crank sensor connected to the speedo??? > > I realize strange wiring is always being invented, but this doesn't > make sense. > > -SP Methinks he meant driveshaft sensor. >> I have this problem in my Maxima while back. The problem was NOT the >> speedo >> but the crankshaft position sensor. This is an easy part to get to (one >> screw) and I'd check this and its cabling first. Replacing speedo is >> a lot >> harder and may cause other electrical problems.  SignatureBill In Hamptonburgh, NY Speedy, in my Max (2002), the CKPS is located at the end of engine near the tranny. The signal from it goes to the engine computer, which evidently drives the speedo needle somehow (its not physical speedo cable like the old days). When my CPS went out I had a hard time starting the car, but once it is running, I was able to drive away fine, but the speedo stays at zero mph ( I think the rpm too, but its been a while...). The speedo indication should not be related to the CKPS as there is no possible way to convert CKPS signal on a vehicle with AT to speed indication (think idling downhill). > Speedy, in my Max (2002), the CKPS is located at the end of engine near the > tranny. The signal from it goes to the engine computer, which evidently > drives the speedo needle somehow (its not physical speedo cable like the > old days). When my CPS went out I had a hard time starting the car, but > once it is running, I was able to drive away fine, but the speedo stays at > zero mph ( I think the rpm too, but its been a while...). AS, intuitively I agree with you, BUT, I still have my "bad" CKPS in my tool box, so I am speaking only from my OWN experience in my Max just last year. I wished I had saved the website that points me to this solution. I remember in my old days speedos are typically driven by a gear attached to the tranny, turning a sleeved cable which drives the speedometer... Could it be that the ECM kills the speedo to let you know that there is something wrong with the ckps? I would imagine the MIL would do that. Or was that the ckps failed in such a way that it was killing the power for the speedo circuit? I am not refuting that replacing the ckps fixed the problem. Good luck > AS, intuitively I agree with you, BUT, I still have my "bad" CKPS in my > tool box, so I am speaking only from my OWN experience in my Max just last > year. I wished I had saved the website that points me to this solution. I > remember in my old days speedos are typically driven by a gear attached to > the tranny, turning a sleeved cable which drives the speedometer... "crank angle sensor" vs "crankshaft position sensor" the original thread was about a 94 nissan sentra, which has a "crank angle sensor" that is mounted inside the distributor. later year models of the sentra have a "crankshaft position sensor", which is mounted on the transaxle bellhousing. the location is misleading, because it is designed to detect crankshaft speed and sends info to the ECM. lets hope chico posts results for us to learn his solution. > lets hope chico posts results for us to learn his solution. Well, some bad news. I went to a junk yard and picked up a new speedo head. No luck. I then asked for the sensor. The guy had a little trouble getting it out of the junk car, but it eventually popped out so I felt pretty confident that I could do the same on my GFs car. The junk sensor appeared to be working (getting 3 or 4 volts AC when spinning it.) Tonight, I tried to get the sensor out, and eventually broke the top part off. Now I have practically nothing to grab onto to try and get the sensor out. Time to ask for more professional help. If this sounds like it's going to get expensive, we may have to bail on fixing it. The timing belt is due soon (yes, only 95,000kms on the car) so that would probably be a good time to get a mechanic to take a shot at extracting the sensor. <sigh> Oh well. Such is life sometimes! Chico >> lets hope chico posts results for us to learn his solution. > [quoted text clipped - 19 lines] > > Chico Can't help you on the broken sensor, but some good news....your '94 sentra has a timing chain so it does't need replacing. > Can't help you on the broken sensor, but some good news....your '94 > sentra has a timing chain so it does't need replacing. Ha! I misread the manual on Chilton's. It said "inspect drive belts." That's good. Spent another three hours trying to get the sensor out today. This thing is not moving. Once my fingers defrost, I might try to get at the ECM. I found the Chilton's manual to be kinda vague. Is it under the centre console, down by the gas pedal? It's a moot point now, but I'd like to find it and confirm the codes. Chico > >> Can't help you on the broken sensor, but some good news....your '94 [quoted text clipped - 7 lines] > thing is not moving. > Have you tried liquid wrench? Before I replaced my bumper, I sprayed the bolts 3 times on three days while waiting for the bumper to arrive. They came out pretty easily for being in there for 10 years. > Once my fingers defrost, I might try to get at the ECM. I found the > Chilton's manual to be kinda vague. Is it under the centre console, [quoted text clipped - 4 lines] > > SignatureBill In Hamptonburgh, NY > Have you tried liquid wrench? Before I replaced my bumper, I sprayed the > bolts 3 times on three days while waiting for the bumper to arrive. They > came out pretty easily for being in there for 10 years. Tried several kinds of penetrating fluid. Did not appear to penetrate. > > Once my fingers defrost, I might try to get at the ECM. I found the > > Chilton's manual to be kinda vague. Is it under the centre console, > > down by the gas pedal? It's a moot point now, but I'd like to find it > > and confirm the codes. OK, while I had the dash half apart I wanted to see if I could read the code. I found the ECU and located the single LED window on the passenger side. Of course, the Diagnostic Mode Selector screw was on the back of the unit, so I had to unscrew and unclip pretty much everythign to get at it. I turned it all the way clockwise, re- attached several wiring harnesses, and turned the ignition to ON. The LED blicked very quickly once, then nothing. I was expecting a code. I still had the two buttons (hazard lights and rear defrost) disconnected from the center console. Could that have been the reason the code was not flashed? Check engine light is still on at the end of the day. Chico maybe the google "reply to author" does not work properly, anyway, did you try to rotate the sensor with a chisel like i suggested? if the '94 sentra is like the US non-california model, you have to be in mode II to extract codes on a MPFI sentra engine. the procedure for this engine is: turn ignition switch on, engine not running, turn ECM screw fully clockwise, wait at least two seconds, then turn screw fully counterclockwise, wait two seconds, turn screw clockwise, wait two seconds, turn screw counterclockwise, the ECM should now be in mode II and will begin displaying codes. if you have the instrument cluster working correctly, the check engine light will flash the long and short codes. also the red led on the ECM will flash the same codes. > OK, while I had the dash half apart I wanted to see if I could read > the code. I found the ECU and located the single LED window on the [quoted text clipped - 7 lines] > the code was not flashed? Check engine light is still on at the end > of the day. > maybe the google "reply to author" does not work properly, anyway, > did you try to rotate the sensor with a chisel like i suggested? Sure did. Had a screwdriver stuck into the end of a 3 foot long massive pipe on which I hammered for a while, to no avail. Tried banging on a crowbar from underneath, from through the wheel well, from on top. No movement. Not much metal left. Only the flange, and it's pretty beat up. > if the '94 sentra is like the US non-california model, you have to be > in mode II to [quoted text clipped - 5 lines] > the ECM should now be in mode II and will begin displaying > codes. Well now. I certainly didn't try that sequence of actions. Chilton's didn't describe that. I've got everything back together now so it'll have to wait until I'm bored again. > if you have the instrument cluster working correctly, the > check engine light will flash the long and short codes. > also the red led on the ECM will flash the same codes. That's what I thought, but thanks for confirming. I'll try a pro mechanic to see if they have any tricks to get that damn sensor out. Chico you might consider trying the inexpensive things first, like (1) check all fuses (near driver's left knee), (2) unplug and replug the connectors at vss (vehicle speed sensor) and speedometer (at instrument panel) to eliminate the possibility of an oxidized connection), and (3) check for 12 volts at vss connector by unplugging connector (voltage check with ignition key on, engine not running). if you pulled the ECM code, you might find that it is indeed a 14 (1 long flash, 4 short flashes), indicating the vss signal circuit is open. > Hello. > [quoted text clipped - 18 lines] > thanks for any help, > Chicobiker Thanks for the replies all. Can someone please confirm for me that the following is actually the VSS: http://www.geocities.com/chicobiker/1000600small.jpg I wish I had thought of checking for 12V at the sensor while I had my hands down there. However, as an electrical person, I'm wondering how only two wires can apply 12V to the sensor, while still bringing back a speed related signal to the speedo head. Unless the VSS is some sort of dry contact that pulsates accoring to speed? > you might consider trying the inexpensive things first, like (1) check > all fuses (near driver's left knee), (2) unplug and replug the > connectors > at vss (vehicle speed sensor) and speedometer (at instrument > panel) to eliminate the possibility of an oxidized connection), and Done. I have the dash apart right now and all connection points look good. I tried to see if I could find where the speed signal enters the speedo head so I could verify that the sensor is OK. I was expecting a 0.5V AC signal but I was not able to find it. Instead I found about 5V DC. I find it interesting that the signals are passed on through to the speedo head via the screws that hold it in place. My next step is to try another speedo head from a recycling dealer, but I'm too late and they are all closed now so I'll have to try on Monday. Here is a pic from the back of the instrument cluster: http://www.geocities.com/chicobiker/speedo001.jpg I was measuring between the two upper screws of the speedo head. Any other way to identify which wires come from the VSS and possibly verify that the VSS is good from the dash before I put this back together? Oh, also, I found that there was no low fuel light bulb. Strange. Chicobiker > http://www.geocities.com/chicobiker/1000600small.jpg that is what the vss is supposed to look like, however, that trannie must have been exposed to a lot of salt? > I wish I had thought of checking for 12V at the sensor while I had my > hands down there. However, as an electrical person, I'm wondering how > only two wires can apply 12V to the sensor, while still bringing back > a speed related signal to the speedo head. Unless the VSS is some > sort of dry contact that pulsates accoring to speed? the vss works in conjunction with a reed switch which is in the speedo head. the reed switch transforms vehicle speed into a pulsing voltage signal that is translated by the ECM. you can get a reasonable idea if the vss has failed, by unplugging the vss at its connector and, with an ohmmeter, measure the resistance, it should be approx. 250 ohms. if resistance is incorrect, remove vss and check for pulses with voltmeter set on AC scale. the vss is supposed to come straight out but the corrosion may make it difficult. > >http://www.geocities.com/chicobiker/1000600small.jpg > > that is what the vss is supposed to look like, however, that trannie > must > have been exposed to a lot of salt? That's no surprise. I live in Nova Scotia, Canada. It's raining today, so I didn't want to try and pull the VSS out, but I thought I had found the culprit as: http://www.geocities.com/chicobiker/relay002.jpg The wires feeding this relay produced a speed dependant AC voltage, so I figure that's a sign the VSS is doing something. It was either 0-0.1V, or 0-1.0V. I can't remember now. This thing is mounted to the back of the instrument cluster. However, I managed to toggle the contact with 12VDC so it's working. So far, the speedo head is my guess. I'll see tomorrow when the shops open up again. I also found Chilton's online through the local library. That is useful stuff. Glad I found that. Chicobiker |
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