An ASE Quiz (Not an Official ASE Test Question)
A 1998 Mustang GT shifts good through all gears and has converter lockup, but the speedometer is dropping out after driving a short distance. The scan tool shows that there is a VSS signal and reads correct speed when the speedometer drops out. There was a code in history for the VSS but after clearing it did not return.
Finally, the truck shows its cards
We’ve all had to contend with intermittent electrical problems. These are typically the most difficult issue to pinpoint, as the root cause literally plays hide and seek with you. The following issue that I encountered belonged to a 2008 Dodge Ram 5500 in which the customer stated the transmission wasn’t shifting, and the check-engine light was on.
Diagnosing Shifting Issues
One of the best and easiest tools that I use almost daily for diagnosing transmission problems is Passbook or application-chart information. When I have a shifting issue, a review of what solenoids and friction elements are applied in each gear can let me see what areas of the transmission the problem may be caused by, so I can then differentiate whether there is an electrical or mechanical issue causing the symptoms.
Premature Overdrive
It seems that we have run into several different vehicles in the recent past that have had stacked shifts, and shifted into overdrive by 20 mph. While the symptoms were the same, the diagnoses and repairs were very different. Here is what we found to be the problem on each one.
Looking ‘Outside the Box’
My first encounter with a Nissan CVT was an interesting experience. Our wholesale customer had diagnosed the transmission as being bad, so the transmission was then replaced. After replacement, the vehicle owner said the car would not accelerate beyond 40 mph. Since the installed transmission was purchased from us, it then became our responsibility to find the root cause of the problem and get the transmission working properly. We verified the customer’s complaint with the initial road test and then began diagnosing the cause.
