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Speedometer/Odometer stuck at 0 on 1995 Pathfinder


muniman01
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Ok folks,

 

I'm trying to fix my speedometer/odometer in my 1995 Nissan pathfinder. I know this is a somewhat common problem, and have looked through some other helpful posts. Still struggling to find exact details for my specific year. So, I bought a Chilton repair manual thinking it would have all the electrical diagrams to be able to diagnose this, but alas it wasn't that helpful. I couldn't find any detailed wiring diagrams specifically for the dash.

 

Any tips from the experts on where I can find a schematic showing what is supposed to be at each wire in the harness? Or just any tips in general on diagnosing this?

 

For completeness, here's the symptoms: A few months back the speedometer started getting twitchy. It would twitch down as you are driving at a constant speed--it never twitched above your true speed (checked with GPS watch). Then, this worsened and eventually got to the point where it would stop working altogether and stay at 0. Often times when the speedometer is stuck at zero the check engine light is also on. The times when it was stuck at zero (as opposed to being twitchy) eventually became more and more common, until now it is always stuck at zero with the check engine light on. The odometer also does not work when the speedometer is stuck at zero. Transmission seems to be functioning normally.

 

Really appreciate any and all help!

 

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:welcome:

 

Download the '94/'95 service manual for free here. EF&EC and EL will be your friends for this one, but you might as well download the whole thing. It comes in handy.

 

Start with the check engine light. The EF&EC section will tell you how to get a code from the ECU, what it means, and what to check to chase it down. My money's on code 14, speed sensor.

 

The transmission computer doesn't have a check light, but it'll flash the light in the E-AT switch after startup if it saw something in the last drive that it didn't like. The AT section has information for decoding those flashes. If you do see the flashes, I recommend recording them on your phone for easy playback, as it may take a few tries to read them properly. 

 

I haven't had to do one yet, but I've heard the speed sensors in these can be a pig to get out, and the drive gear may be difficult to track down/not included with the new sensor. Test and make sure you're on the right track before throwing a sensor at it. 

 

Good luck and let us know what you find!

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@Slartibartfast

 

Thanks for the super helpful response!

 

I followed the diagnostic flow charts in the service manual (relevant pages seemed to be EF&EC-38, EF&EC-39, AT-39 through AT-42, and wiring diagrams on AT-36 through AT-38). You're right on the money, ECM has a code for 14--vehicle speed sensor. Going through the diagnostics in the AT section showed that "Vehicle speed sensor circuit is short circuited or disconnected" (AT-40). This prompted me to check the voltage at terminal 24, see attached screenshot from the manual.

 

I'm a little confused by this check--am I supposed to measure the voltage at the harness when it is disconnected? Or am I somehow supposed to measure the voltage at this terminal when the harness is connected to the control unit (not sure how I would do the latter)?

 

I disconnected the harnesses from the A/T control unit and measured the harness side voltage while my dad was driving 1-2 mph. I was seeing readings of 1-3 V, which supposedly is normal according to this flow chart. The spec of 0-5V shown in the flow chart seems super vague though. Any ideas on where to go next?

 

One other thing I noticed: the diagram on AT-38 shows the vehicle speed sensor going through the speedometer before going to the ECM and A/T control unit. So since my speedometer isn't working, and yet my A/T control unit is apparently getting an acceptable signal (if I did the test correctly), wouldn't this narrow the problem down to the speedometer servo motor (or whatever physically drives the needle)? Although this wouldn't explain the engine code...

 

image.thumb.png.22f8306c9402c820e7451c0ffd22ec40.png

Edited by muniman01
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GI-13 says the "connect" icon in your screenshot means you should test with the plug connected. Most connectors can be back-probed. You can get kits to do this more easily, but the way I do it (and I'm pretty sure there's a picture of this in the manual somewhere) is to wrap a thin wire around the lead on the meter, then stick the end of that wire into the back of the connector beside the wire that you want to test, so the test wire contacts the pin inside the connector.

 

The box that says HS above the "connect" icon means the connector is shown from the harness side, which makes sense, as that's the side you're probing from. 

 

The wording is a little vague, and I haven't dug into this circuit on a round-dash truck, but I think they mean you should see 5v, then 0v, then 5v, then 0v, repeating as the truck moves. My understanding is that the speed sensor is a reed switch mounted next to a magnet on a shaft with a gear on the end, which generates a square wave signal as you drive. Each cycle (on/off) translates to a distance travelled. Try the test again, backprobing this time on the off chance that matters in this case, and see if that gets you a 5v square-wave signal. 

 

My '93 has the older style of cluster (square-dash), which has the speedo/odo driven by a spinning cable. The reed switch that makes the speed sensor signal for the computer(s) is built into the speedo. 

 

If you try the test again, and don't see the square-wave, I would check the harness between the speed sensor and the cluster, then see if I could test the sensor itself. If it is just a reed switch, you should be able to test continuity across it (harness unplugged, just the sensor), turn the sensor (could just put the rear axle on jack stands, trans in neutral, and turn the rear driveshaft by hand), and see if the switch cycles on and off as the shaft goes around. Again, I haven't tried it--but that's what I'd try next.

 

Now that I think about it, I've got a round-dash speed sensor in a transfer case on my shop floor, and I'm pretty sure the speedo worked in the truck I pulled it out of. If I remember the next time I'm down there, I'll have a poke at that one to see if it tests the way I think it does. 

 

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  • 2 weeks later...

Ok, I've been busy with life but have finally gotten a chance to perform some of these tests. I tested the voltage at the A/T control unit again except with the connector installed. This time, it read a constant ~5V while moving along at 1-2 MPH. So clearly, not the square wave that it should be.

 

Next, I tested the continuity from the this wire to where it comes from behind the console. I used the wiring diagram on AT36-AT37 to find the correct terminals. The continuity was good (1-2 ohms).

 

Next, I tested the continuity of the reed switch itself. I believe it is the sensor at the back passenger side of the transmission that looks like this (https://www.oreillyauto.com/detail/c/import-direct-ignition/brakes/anti-lock-brake--abs--parts/vehicle-speed-sensor/e06e4f5f9dc5/import-direct-ignition-2-terminal-vehicle-speed-sensor/odi0/130122/v/a/6749/automotive-suv-1995-nissan-pathfinder?pos=0)

 

I was getting an open circuit at this sensor regardless of where I had the driveshaft positioned. Based on this, I must assume that this sensor is the problem. However, if the reed switch truly is stuck open I would have guessed that I would see 0 V at the A/T control unit terminal from this sensor rather than the 5 V I was seeing-assuming the 5 V signal is sent through this switch and then directly to the control unit. But who knows, maybe the circuit pulls the terminal at the A/T control unit to 0 when the switch closes. I am wondering, could a sensor like this really cause (what started as) an intermittent problem?

 

So, I'll plan on replacing this sensor and see if that solves my issue. Can I simply replace the sensor without draining any fluid, or will fluid come spilling out of the cavity when I remove the old sensor?

 

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Sounds like you've tracked it down. I wouldn't expect a reed switch to fail intermittently, but maybe something came loose inside, or the contacts fouled. The contacts opening and closing might've worn through the fouling a few times before it stuck for good. Might also be the drive gear is missing a couple teeth, and sometimes it stopped in just the right place to where it wasn't driven. Hopefully you don't get it apart and then have to go track down a gear.

 

The sensor pulling a 5v line to ground sounds reasonable to me. Could also be that the cluster or engine computer modifies the sensor signal in some way before sending it on to the transmission computer. I have no idea if those connections are straight through or not. 

 

Not sure on the fluid. Find the fill hole for the transfer and see if it's higher or lower than the speed sensor. If it's lower, then yes, you'll have some ATF come out to say hello.

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Well, the sensor does not appear to be the issue. The new sensor arrived today so I took the old one out, only to realize that the shaft of the new sensor is shorter and so is not a direct replacement. While I had the one out though, I figured I'd do some more testing. I unfortunately do not have an oscilloscope, but I rigged up a simple program on my Arduino to test resistance vs time of the sensor. The old sensor behaves quite similarly to the new one -- it's around 300 ohms at rest, and then runs about 4 periods of a waveform when the shaft is rotated one full turn. The old sensor does not feel as smooth (which is evident in a slightly more jagged waveform) and also does not have quite as large of an amplitude. However, if seems to behave similarly enough that I doubt this is my problem.

 

One thing I did notice is that the gear was a tiny bit worn down. Same deal, I don't think this is enough to cause my problem. I suppose that once I put the old sensor back in I could plug my "oscilloscope" into it again to make sure that the driveshaft is turning the gear.

 

I have pictures of the waveform that would be fun to share, but they are a few hundred kB. It looks like the max upload for a post here is 8.45 kB--how do I work around this limit?

 

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So I put the sensor back in, hooked up my "oscilloscope" and spun the driveshaft only to see no waveform. Then I pulled the sensor out and peered in and found that the gear inside the transmission is also worn down, although slightly more than the one of the sensor. With both of these worn down, they are just no longer grabbing.

 

I'm happy because I've finally found the problem; but I don't think fixing this is worth it to me. I would have to disassemble the rear transmission casing in order replace that gear. Historically, I don't have good relationships with gaskets and aluminum cases. But, if someone chimes in saying that this is an easy disassembly I might consider it. Otherwise, I'm going to live without a speedo/odometer.

 

Thanks for the help @Slartibartfast, your wisdom is much appreciated!

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Good work tracking it down! I like the Arduino scope, that's clever.

 

I've heard of the gear on the sensor breaking, but the one in the transfer going is a new one on me. I haven't been into one, but it doesn't look like it would be terrible to get to, apart from the fun of working over your head on something that wants to leak fluids on you. Nissanpartsdeal lists what I think is the right part. The case is sealed with silicone, not gaskets, so at least you don't have to try and keep a gasket in place while you line stuff up. If both gears are worn, but not broken/chewed up, I would be tempted to replace just the one on the sensor, to see if that gave it enough engagement to work again. It's not like it's transmitting a whole lot of torque, right?

 

Posting pictures here usually means hosting them elsewhere, unfortunately. 

 

Edited by Slartibartfast
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Years ago, I tried to take the transfer case apart on my 95 D21 with the KA24 engine. I don't know how different the transfer case is, but I gave up on splitting the case. I couldn't seem to wiggle my nose just right to get the case completely apart. I'm sure there's a trick to it. It's a heavy little pig for sure though.

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  • 2 weeks later...

Well, I've thought about it some and finally decided I'll make the effort to fix this. Just ordered both gears. I'll take any and all advice for cracking the AT open (and getting it back together again)! Also if you know of any tools/stuff I will need other than basic hand tools let me know so I can get them in advance.

 

So when I seal it back up, I can just use any old silicone, or is there a specialty formula that I need to use?

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I'm not sure what the factory used. The service manual calls for their KP610-00250 sealant "or equivalent." The description on NissanPartsDeal says "gasket-liquid," which does sound like Hylomar, but it also says FIP, which I assume is form-in-place, which has me thinking silicone. Let us know what you find when you tear it down! I would expect either type of sealant to do the job provided it's applied properly and the mating surfaces are clean. Unless I had a good reason to use something else, I would use black RTV. 

Seals are a good idea while you're in there. A seal that isn't leaking yet may change its mind after being disturbed. My front crank seal did that after a timing belt change.

 

I haven't opened one of these transfers, or dropped one on its own, so I don't have much in the way of specific tips. The shift linkage is removable, that might save you some trouble. If you drop the whole transfer case, a transmission jack will make your life much easier. You may need another jack to support the back of the transmission while the transfer is out. I would be tempted to try and remove the back case half without removing the rest of the transfer from the truck, if there's clearance for that vs the torsion bar crossmember. If you need to remove that crossmember, 1) make damn sure the front end is on jackstands first (the torsion bars hold the front end up) and 2) mark or take a picture of the adjusters before taking them apart. They're a bit fiddly to adjust, so having their starting position marked in some way will save you some time trying to trial-and-error it back to where it was. 

 

Oh, and you'll need some way of getting oil back into it when you're done. A hand pump will do, slowly. I fabricobbled a jar with a hose and an air chuck to make it easier. When a friend and I dropped the transfer from an Exploder a while back, we overfilled it, installed it, then removed the fill plug to drain the excess. Worked great.


 

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  • 1 month later...

Ok, I’m into this project now. I’ve got the driveshaft, torsion bar, and torsion bar crossmember off (I’ve also drained the fluid). I’m hoping to just need to remove the rear cover, not the entire transfer case. So I’ve got all the bolts for this rear cover off and the cover is sticking; it won’t budge. There are some pry points that I’ve pried from with a flathead screwdriver. I could pry harder or introduce a rubber mallet, but I’m concerned about inflicting damage. Do I just need to bring more force or is there a trick that I am missing?

 

I’m also slightly concerned that parts inside the transmission/transfer case are being supported by this rear cover and will fall off once I remove it—and potentially be super challenging to install back together again. Kinda just moving ahead anyways, but would welcome any wisdom on whether this is a legitimate concern. 

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Got it off, just took some more force! It’s all back together now with the new speedometer gear, I just got to let the silicone dry before filling back up with oil. The speedometer gear was VERY worn out. Had some hiccups along the way. Mainly getting that cover back in place was a pain in the rear, so I’m kinda concerned about the quality of the silicone seal. Also, I lost my reference on one of the torsion bars so will have to adjust that one back to level once I drop the truck off to the jackstands. I’ll update y’all once I finish it up. Probably won’t be this week unfortunately.

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