Overdrive problem solved

Last driving season my 84 Corvette (with 4+3 manual transmission) had an overdrive problem. After the mandatory engine warm-up the overdrive would inexplicably cut out during the drive along with a “check engine” warning. Sometime later during the drive it would inexplicably engage with the “check engine” warning light going out.

A test with my $49.95 code reader yielded code no. 15 “Coolant temperature sensor or circuit fault - signal voltage high”. I took it to my local mechanic. He used his “professional” code reader and got 4 additional codes. He gave the car back to me and said “I’m baffled, I don’t even know where to start”.

After many hours studying the GM schematic diagram for this car, I discovered something surprising. There are two engine temperature sensors. One on the left side of the engine has only one wire going to the instrument cluster. The other on the front of the engine has two wires (twisted pair) going to the car’s computer. I had replaced the former a couple of years ago, so I focused on the latter. I removed it’s connector and inspected it. It  resembled a coaxial connector, similar to cable TV.  It seemed free of corrosion or dirt, so I reconnected it. As if by magic, the next time I drove the car the overdrive worked perfectly. It has worked perfectly ever since. Somehow the act of removing and reconnecting the front engine temperature sensor connector cured the problem.