I have a challenging issue with my Volvo. I have already taken it to two mechanics and they charged me a lot of money to repalce a solenoid valve. The problem came back soon afterward.

Here is my problem: While driving, the speedometer will start jumping around and jittering, sometimes dropping to zero. Once this happens, my automatic gear shifting goes bonkers and drops to lower gears randomly then back up to higher gears. If I am trying to accelerate, the RPMs can jump way up from the lower gears. As expected, the up arrow error light starts blinking and will stay on.

I found a way to get the error light to turn off by shifting down through my gears with the engine off and ignition switch in second position but it comes back once my speedometer starts failing again. This makes me think that the speed sensor or wiring to the TCM is bad. I know the TCM compares the speed and RPM of motor and uses that to shift gears so I figure if the speed sensor for the vehicle sends a bad signal, the tranny will slip up. I took a peek at the connector for the speed sensor located in the differential and it looks OK. Maybe I should check where it connects downstream but I don't know where that is.

Anybody have an idea how to proceed? I don't have a lot of tools and my car knowledge is pretty bad so taking major components apart (especially underneath the car) is not the best option for me. If I can't fix this issue I will have to say goodbye to this car.

 

This may be a dumb question.


Have you replaced the speed sensor?

 

Also. These cars have OBD. Read the link below and all of your question will be answered.


Volvo 960 automatic transmission diagnosis service manual

 

Long shot but did you ever figure this out? Having the exact problem with my '93 960