QuestionTransmission occasionally fails to shift into 4th gear as indicated by monitoring engine tach reading. Problem is remedied by manually shifting into 3rd gear and then manually back to D (overdrive?)and tach reading immediately drops from approx. 2600 to 2000 rpm (@70 mph) and operation is normal.
Car has 109K miles, but has always had this problem. I have been unable to demonstrate condition for Mr. Goodwrench nor does subsequent check of "codes" indicate any problems.
Transmission has recently been serviced for fluid/filter changes without improvement of this condition.
AnswerHere is a simple way to test the overdrive circuit.
1. maintain a speed of 60 mph with your right foot and the AC OFF.
2. While still holding your speed at 60 mph, use your left foot and slightly apply the brake pedal while watching your tach and as soon as the brake lights come ON you will feel a slight bump and a decrease in the tach speed.
Release the brake and you will feel a slight bump with an INCREASE in tach speed.
If you feel and see this with the tach your overdrive is working. If you do NOT see the tach change or feel the slight bump, Then the overdrive is NOT working.
It is VITAL that you get to 60 mph and hold that speed, Do NOT increase your foot pedal speed at any time.
