Have a 1999 2WD Tahoe with 169,000mi. Have had all the common issues over the years: dead fuel pump, lower intake manifold gasket leak, 2 alternators, starter, corroded distributor cap causing had/no start when wet, broken drivers side door handle. Fixed them all. However, have an issue I can't figure out. The old Hoe recently started kicking in and out of overdrive around 40 to 50 MPH under light acceleration/cruising. Now here's the strangest part...I can reproduce the issue in most cases when I turn the wipers on. Yes, when I turn the wiper to mist (when wiper goes back and forth only once) or turn them to delay the truck kicks out of overdrive. I swear I am not crazy. I changed the transmission fluid without taking off the pan (I have a Pella oil extractor) because I used Lucas additive in the past to stop a leak and wanted to remove it to rule that out but that didn't help. I plan on dropping the pan and changing the filter when it gets warmer out. Only reason I have not done that yet is because I think it's electrical. I replaced the wiper pulse board in case it was creating a short as it was covered with grease on the inside and showing wear but that did not fix the issue. Any ideas? Here is a link to video of me reproducing the issue 3 times just by turning on the wipers. It looks like a fake youtube address but it is correct. http://youtu.be/EfK8kVya-mM
1999 Tahoe Overdrive Problem
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Did some more searching online last night a found someone else having a similar issue in the 99 Tahoe. In their case they were having the OD kickdown but also their cruise control would disengage. I never use CC so I tested it today and wouldn't you know it, same thing happens. While cruising 45 to 50 mph in overdrive with cruise set if I use my wipers my transmission kicks out of OD and my cruise control disengages. In that post it was mentioned that the common circuit/switch for these 2 things is the brake switch. It's cheap enough to replace and will give it a try. Will post the results. In the meantime, does it make sense that my wipers will somehow send a pulse/signal to the brake switch?
Update...bought new switch. Went to install it last night but could not get the clip that holds the switch and brake rod off. Very tight space and need a very small pointed needle nose pliers. While I was down there I moved it around a bit and made sure the wires were seated properly and secure. I now cannot reproduce the issue. Definitely seems like I found the problem area. Going to change out the switch anyway when I get the proper needle nose pliers.
clkelley
Moderator
Good to hear you have narrowed it down!
