QuestionHi. I found your information from a previous post helpful to a certain extent, but wished it went just a little further. I recently got a used car, a '94 Corolla, 1.8 Liter/Auto trans, that the speedometer intermittently quits working. That progressed to where sometimes it will affect the transmission shifting, to where it will go from first gear in an auto transmission to neutral. The transmission normally shifts normally, and smooth. And it is not slipping when it does shift normally.
In the post I read, you mentioned a second speed sensor of some sort that feeds directly to the computer, that WILL affect shifting if it is not working, that also sets a code 42 on this vehicle. Can you elaborate a little more on that, as to where it is located, and whether I would have to replace the whole speedometer assembly if the speed sensor is an integral part of the assembly, first check some electrical connections perhaps, or the like? I am fairly proficient working on cars (mechanically inclined), and have had quite a bit of experience working on cars, but have never run across this problem before now.
AnswerThe most likely cause for this is the speed sensor that's mounted on the transmission, this is where the signal for the speedometer originates, the sensor in the speedo then sends this signal to the computer, I have only seen a few isolated cases where the speedometer was at fault and likely could have been caused by an intermittently shorted out sensor so I would recommend replacing the speed sensor, just recently I had the same problem with a '94 Camry which uses the same exact principle as the Corolla and replacing the speed sensor in the transmission took care of the problem. The sensor is located on top of the transmission, it has a single 10mm size bolt on it and an electrical connector, the new sensor does not come with the driven gear so the gear has to be re-used form the old one.
