Volvo 670 help needed
 

I have Volvo 670, few days ago a faced a problem my speedometer stopped working(when you go 50mi/h it shows 20 mi/h)
Also sometimes the check engine light flashes and engine starts loosing it's power but when i release and press again gas pedal everything get's to normal.
(The interesting thing is that speedometer stopped working when check engine light first time started to flash)
Does anyone knows solution of such a problem?
Thank you

Check ECM wiring on the battery.

VSS (vehicle speed sensor) at the transmission output shaft is defective, or the connections or wiring between the VSS and the ECM have a fault.

When the ECM does not receive a valid signal from the VSS, the speedometer will read inaccurately or not at all and it will not allow the engine to operate at full power, hence the loss of power when the speedometer is reading incorrectly.

The check engine light is notifying you that the ECM has detected a fault in the system i.e. the problem with the VSS.

volvo speed problems
 

You need to check if the problem happens when you try to acelerate or is it all the time. I have the same problem on my volvo, and FLD as well. I called Cummins and got many answers. The one I liked best was when the superviser said check the wire that goes from the VSS to the ECM, it could be bad since it was only happening when I went accelerate. The engine would twist under torque and I would lose my speedo display. As soon as I let off, the speedo would show normal. The Odometer will be out that much as well. As far as loosing power, that is because when the speedo reads below 10k/hr, and the RPM is over the setting for no VSS signal, the electronics go into a preprogrammed setting as if you did not have a working VSS, therefore no power. It took me while to figure out all these things. If you dont want it to lose power, go to Cummins or Freightliner or CAT, and have them reprogram so that the RPM will go to 1800 even if you don't have VSS at any time. Hope this helps.

Re: volvo speed problems
 

Why not just find the real problem and fix it the right way?

no kidding, quicker and cheaper too.

It is the VSS sensor. Replace it is is only $32.00 for the part.

Doesn't the vss have to be adjusted/calibrated also?

On the Volvo's there is a second VSS on the top of the shaft. The one that is being used is probably on the side. Unplug it and use the second one to see if that solves your problem. Have you noticed if it acts up ALL the time or only when it is fully warmed up? Mines will only do it after it has been running for about 1/2 to 1 hour. Then it will continue to do it after that.