Is your blower working properly?Is it blowing out the vents,good,Is the blend door open for heat.Click here to see how to adjust.If it's the heater core,brrr,then click here to see how to replace.
Yes it does but only indirectly. Keep in mind the PCM is the very least likely part to cause a problem with the speedometer. The common problem is the tiny little motor that moves the needle files.