Hey everyone,

I am having a problem with the speedometer in my truck.

96 Tacoma Std cab
4X4
2.7L
5 Speed

The speedo does not read the correct speed, it shows a much faster speed, but always by different amounts.

Since it is a manual, I know my speed from the tach and what gear I am in.
Sometimes I will be going 25mph and the speedo will read 40 or 50, other times at the same speed the speedo will be pegged at 110, and sometimes it will be accurate. (the odometer always works properly though)


I bought a scan tool today to further see what is going on. The speed display on the scan tool is accurate, even when the speedo is not.

I crawled under the truck and disconnected the cable for the speedo at the back of the tranny, drove the truck again, this time the speedo did not move and the scan tool showed the speed at zero.

I traced the cable from the tranny and it goes into the firewall just behind the instrument cluster.

So, is the speedo bad?

How does the computer know the correct speed when the speedometer dispays the incorrect speed?

Thanks.

 

I have done some more reading in the FSM, and now have some more info to go on.

The cable from the tranny goes into the instrument cluster where there is a speed sensor. For every 1 rotation of the cable, the speed sensor sends out 4 pulses. From searching google, the cruise control ECU uses these pulses to know the speed of the truck. I have no cruise control, so I am assuming that the signal from the speed sensor is being sent to the ECU. If that is the case, then the speed sensor must be fine, since the ECU is showing the correct speed.

The FSM has a procedure to test the speed senor by checking to see if there is continuity between the two terminals 4 times for every 1 revolution of the cable. I suppose I could check this, but since the computer knows the correct speed, this must be working properly.

I am assuming the speedometer is a mechanical speedometer, and that there must be something wrong with the inner workings of the speedometer itself, since that is the only part of the whole system that is not working properly.

Does anyone know if it is serviceable, i.e. can I pull out the instrument cluster and clean or lube any parts to hopefully get it working again, or do I need to replace it.

Thanks.

 

Found more info, according to post #25, the speedometer can be dissasembled and cleaned/lubed.

https://www.yotatech.com/forums/f116...-cable-198460/

Hopefully I can pull it apart this weekend. Will take pics/video to document for future needs.

 

Well today I pulled apart the dash and took the speedometer apart. I cleaned up the insides and so far it is working much better. Not sure how long it will last though. I have a video of what I did. It is a little long since I don't have any editing software yet.

http://www.youtube.com/watch?v=fgZrlNAg1bY

http://www.youtube.com/watch?v=dQT43wM7vVA