Intermittent Speedometer

Speedometer/Odometer intermittently goes out, it'll sometimes stay at '0 mph' for miles and miles, other times it just dips for a second, then goes back to normal.
Tachometer continues to work normally when this happens.

Not really a big deal except for using cruise control on long trips, when the speed drops to 0, of course the CC drops out and has to be turned off/on to get working again.

I am trying to troubleshoot it out and not just throw parts at it.

I would like to determine if the problem lies in the speed sensor at the rear of the tranny, or if it is the "Combination Meter" (aka, instrument cluster) itself, or even if it is the ECM.

My electronics background is telling me it's a crappy solder joint, probably on the circuit board of the Combo Meter, but I have not taken the needles off to get to the front of the circuit board yet.

There is no rhyme or reason when it drops out, it just does...

Has anyone seen this before or does anyone have any ideas/tips on the best way to troubleshoot this?

Truck is an 05 Tacoma Access Cab, 6Cyl, 6 Spd Manual Trans.

 

Have you inspected the connector at the speed sensor?
Maybe it’s not making good contact or has corrosion?
That’s the easiest thing to check first.

 

Thanks for your reply.
I've inspected that connector and gave it a decent quick cleaning, it all looks good down there.
Wires are not brittle, contacts are not corroded.
Just cause it looks good, does not mean it is however.

I just want to try and eliminate as much as I can before I start tossing new parts at it.
It's rather strange to be scooting along and look down to see '0' on the speedometer, even when you get a bit used to it, it's still strange...

I found a wiring diagram on the 'net and I am going to attempt to tap the wires coming from the speed sensor to the combo meter tomorrow, I just want to see if there is still any voltage on the pair of wires when the speedo shows '0'.
I figure this might tell me something at least...
(I am not sure I will see anything though, if it's a CAN circuit I may not see anything as far as a DC voltage on the wire, I could be wrong though, I know pretty much nothing about CAN bus technology, but if it's more of a "data" signal it'll be a square wave and my multimeter probably wont catch it)

 

I will be going after the red/yellow wire and the solid white wire that are going into the combo meter, according to this:


Hopefully I will not break it further!

 

Mine turned out to be the combination meter after it quit working several times after the speed sensor & speedo gear replaced a few times. Works perfect now.

 

I would also verify voltage on the Pink wire from the IG1 Fuse to the speed sensor.

Not much to that circuit: Speed sensor, Wires, IG1 Fuse, Combination Meter and ECU. I would also venture to say that the Most Likely issue would be in the Combination Meter. I base that on the fact that you do not have a CEL for the speed sensor. The flow of data goes like this:

Speed Sensor >> Combination Meter >> ECU

Seems odd you have no CEL for the speed sensor.

EDIT: This theory gets muddy quickly as I reread your post and you are dropping out the cruise control which is controlled by the ECU. So I guess that the ECU is also losing the SPD Signal, Purple Wire with a White Stripe between the Combination Meter and the ECU.

Make sure you check all the wires and connectors between the sensor, combination meter and ECU.

 

Roger that @Jimmyh. Thank you for the reply, you've helped alot, that verifies that my thinking is correct and I am reading the wiring diagram at least partially correctly.
Seriously, Thank you! It's good to know I am not chasing the wrong thing completely!
That is the Ignition Switch correct? aka: the Key
(that would explain why I didn't see a pink wire before, I was looking in the wrong place!)

I'm taking it apart again tomorrow so I will see what I find further.

I will update what I find here. We are not the first owner of this ole Taco, I've already found some other odd "wiring jobs" behind the stereo console.

*edit* and yes, you are correct, there is no CEL for this, ever... I've even disconnected the sensor and not gotten a CEL

 

well. maybe I can see the pulses, my multimeter might be fast enough to at least see something is going on.
I wish a had small more portable o-scope.
I will verify that the sensor is getting power at least.

I hope it's not the combo meter, dang thing is 400$ and takes weeks to get from the dealer, I do not have the ability to reprogram the Odometer into it myself, they'd have to do that.

 

The Pink Wire goes from the 10 Amp IG1 Fuse on the right side of the drawing to pin # 1 on the speed sensor connector. It should read battery voltage.

 

I think that sensor is gear driven so if you remove it from the transmission and have it still connected to the connector you may be able to turn it by hand and see if it is going on and off with the meter as you slowly rotate the gear on the Red With a Yellow Stripe Wire Terminal 3 (SI). Should see 4 pulses for every rotation of the shaft.

 

Thanks! I will let you know what I find out tomorrow.

 

Well...
I went to setup for taping into the wires behind the combo meter and I found what might actually be the problem... some funky prior wiring job... of course.
I peeled back what looked like sheathing but turned out to be electrical tape and found this:

(I peeled back some shrink wrap to expose the solder joint for later)
I had not noticed that before, the connector end of the Purple/White was tucked into the rest of the wires and the rest of it was tucked up under the "sheathing"...
I went ahead and spliced into the wires I was after anyways, since I was in there.
I am going to repair the Purple/White wire and put it back how the wiring diagram shows it to be.

Meanwhile, back down at the transmission...
I did manage to verify that the pink wire on the VSS is at battery voltage when the key is in the 'On' position, so that's good...
I undid the screws to remove the VSS, or least what I think is the VSS:

But, behind that black cover is just a little black spindle looking thing, with a spring in the center, nothing "came out" along with the cover (other than some tranny fluid). The black cover just appears to allow signals/power to pass to/from whatever is inside spinning around.
At that point I have stopped and I figure I have now "totally fubar'd it", I expected some sort of gear mechanism to come out of that hole.
Do I need to remove the bolt above the black connector?

 

Yes just remove the one BOLT and NOT The three screws.

It should come out like this with a gear and shaft on the business end. See this post: https://www.tacomaworld.com/threads/speedometer-and-odometer-error-corrected-easily.293134/

 

That would explain it.
I had to drive after I took that cover off and it all seems to work as well as it did, so I am glad I did not fubar it.

I will pull it tomorrow and see what I can find. Thank you!
I'm a digital person, not mechanical, but I am still a nerd and learning quickly!

I keep thinking about the funky splice up at the combo meter connector.
I also keep thinking about that diagram you posted, and one key sentence from it, that has to do with that splice...
"The 4-pulse signal is converted into a more precise rectangular waveform by the waveform shaping circuit inside the combination meter."

So now I wonder if someone either removed one of those "speedometer calibrator" computers and then tried to "fix" it, or tried to bypass the combo meter entirely in order to keep the cruise control from stopping when the combo meter failed (which would seem to be stupid and possibly dangerous).

 

Yes probably a speedometer calibration doohickey. I can think of no other reason to tap into that wire.

Good luck I hope you get it.

 

I wonder if that splice was used to recalibrate (roll back) odometer

 

With my luck it was that.

I reconnected the purple/white wire properly today, undoing the splice.
Drove only a small distance today, speedometer did not work for the first few minutes after start up, but then started working normally and stayed working all the way home.
At least I did not break it more than it was already.

I think at this point, I will just see how it performs and if the problem continues.
I do want to test the VSS eventually though.
I am going to be driving a couple hundred miles this weekend, it'll be a good test.

Thanks to all for the help so far!
73

 

Hope it remains good. Update when you get back from your trip.

 

I will.
At least I know it's not any worse off so far.
I expect it to be the same, but am keeping my fingers and toes crossed.

One step at a time and I will figure this dang thing out.

Thanks again for your help so far!

 

Small update:
Got a chance to drive the ole girl today and the speedo is still the same.
Although it does seem like it stays "on" more than it was when the splice was in place.

Still, for a moment or 6 after start-up, the speedo reads '0', then it suddenly jumps to life and seems fine.
After it comes to life, I haven't noticed it dropping out while driving after that... yet.
I guess time will tell.

Maybe on Sunday, I will get a chance to pull the Speed Sensor itself and test it.
Too much packing and preparing now, we have a trip up to a repeater site on Saturday...
This is not a great picture, but still: