Reader Question Hi,
While driving on the freeway, the illumination for the odometer and gear shift position on my 1998 GMC Safari van began dimming then brightening again.
Soon the transmission began down shifting to 3rd then back to drive. After a mile or so everything went back to normal and I drove the last 85 miles home.
In the morning the car started fine, but the area of the odometer was dim and then went blank. While driving the transmission never never seemed to shift to drive and might have simply stayed in one gear (3rd I think) the whole time.
After stopping the car and turning it off I could get the lighted odometer area to again be illuminated as I turned the key on, but as soon as I started the car it went blank again.
Hey there Mark
You kinda got me on that one. I would need to run some tests to see what is happening…..or not happening. During the first paragraph of your message I was ready to condemn the alternator but you did not mention anything about a dead battery or having to jump start etc. etc.
The second thing that came to my mind was a VSS vehicle speed sensor, which sends the data to the speedometer. When they fail it usually affects the transmission shift pattern or restricts the transmission from shifting altogether…like you mentioned.
BUT I have not seen a VSS affect the illumination of the dash board like you mention is happening.
I think I would spend the money and time to visit the dealership and get a proper diagnosis before I did anything on this vehicle myself. Keep me posted will ya?
Another reader follow up
I’ve been dealing with transmission problems for friends and family and a real pattern is emerging with electrical problems being the true source of transmission limp mode.
Not only in GMC but in Chrysler products as well.
With GMC products the dash lights start to show an electrical fault with dimming and burnt fuses, lighting.
With Chrysler, using factory made fog lights blows fuses while touching the headlight switch becomes hot enough to feel like touching a lit cigarette lighter.
In the end, replacement of the vehicle speed sensor and the torque sensor correct the problem, for some temporarily, for others, permanently.
The question is, what blew those sensors?
A Mister Transmission mechanic I had this conversation with felt my 93 Chrysler Intrepid needed a new alternator.
The problems started after offering a boost and the theory was that doing so had burnt out the diodes in the alternator, eventually affecting the sensors.
I replaced the speed sensors before changing the alternator and the trani worked fine so I wasn’t sure it was the alternator. Although I haven’t had a problem since.
Other sources, faulty headlight switch at manufacturer?
Under powered electrical for these vehicles?
Voltage spikes for whatever reason?
Short somewhere in system?
Auto door lock/cruise control/airbag problems (poor design)
All the electrical seems to run off one circuit. Cheap and lazy for manufacturers. 😉
Funky electrical issues are the norm and not the anomaly with transmission problems.
The sad part, the codes indicate a transmission problem because they pick up the fault at the device affected, not from the source of the problem.
What is req’d on computerized vehicles is a code system to monitor the electrical output of the computerized system before troubleshooting the devices these electronic signals feed.
I have spoken to so many people who have rebuilt their transmissions only to find the vehicle is still having problems.
One tranny guy quoted me $4000 for a rebuild, when $80 for two sensors fixed the issue.
The tranny guy would replace the sensors as part of the rebuild which meant no one would have discovered the true problem.
My two cents worth – pass along to Mark – he’s reading it right.