Vehicle had a rough automatic transmission shift and erratic speedometer when vehicle warmed up. I've replaced both output and input speed sensors. Now the speedometer does not work and transmission won't shift from low.

With today's cars and trucks, your speedometer's reference doesn't come from a spinning cable connected to the transmission anymore. It comes from a pair of wires coming from a sensor connected to the transmission. This is your vehicle's speed sensor.

In some applications, there are 2 of them, but we'll concentrate for now on the transmission's output shaft speed sensor. This is the one that is cruicial in telling you how fast you're going down the road, courtesy of your vehicle's computer reading its signal and then translating that information to your speedometer. The computer also uses this signal in order to help determine fuel delivery, ignition advance, transmission shift points, etc., based on the vehicle's speed.

That being said, it's an important little sensor! And might I also say that it is fairly easy to change and is fairly inexpensive. But let's look at your speedometer. Are you getting erratic (jumpy) readings on it? Is it just stuck at 0? Is it wildly inaccurate? Is your computer-controlled transmission shifting erratically as well? Chances are, if you have one or more of these problems, you may want to first look at replacing your output shaft speed sensor. If your vehicle has 2 (input and output shaft sensors,) replace them both. They're inexpensive and chances are, if one is bad, the other has aged the same way, so it will be beneficial for you to change them as a pair.

How inexpensive are these do you ask? Well, at most auto parts stores, you'll be looking at spending no more than around $15-$20 each, Depending on the year, make and model of your vehicle of course. Also depending on your vehicle will be the amount of time for replacing it (them.) I recently replaced both sensors on a '98 Dodge Caravan and it took me around 15 minutes or so, and I wasn't in a huge hurry to finish, either. Again, depending on your vehicle, the location of your speed sensor(s) will vary. The Dodge Caravan's were located on the driver's side, way at the front of the transmission, allowing very easy access.

So, if you have any of the above-mentioned problems and care to tackle the problem on your own, do so before going out and buying a new instrument cluster. (Yes, I've seen many problems on here where the automotive technician was quick to replace the cluster, costing the customer hundreds of dollars, and ending up with the same problem!)

I wish you safe driving in the coming seasons and most of all, I wish you good driveability!

Kind Regards,
Jason_MKG

With today's cars and trucks, your speedometer's reference doesn't come from a spinning cable connected to the transmission anymore. It comes from a pair of wires coming from a sensor connected to the transmission. This is your vehicle's speed sensor.

In some applications, there are 2 of them, but we'll concentrate for now on the transmission's output shaft speed sensor. This is the one that is cruicial in telling you how fast you're going down the road, courtesy of your vehicle's computer reading its signal and then translating that information to your speedometer. The computer also uses this signal in order to help determine fuel delivery, ignition advance, transmission shift points, etc., based on the vehicle's speed.

That being said, it's an important little sensor! And might I also say that it is fairly easy to change and is fairly inexpensive. But let's look at your speedometer. Are you getting erratic (jumpy) readings on it? Is it just stuck at 0? Is it wildly inaccurate? Is your computer-controlled transmission shifting erratically as well? Chances are, if you have one or more of these problems, you may want to first look at replacing your output shaft speed sensor. If your vehicle has 2 (input and output shaft sensors,) replace them both. They're inexpensive and chances are, if one is bad, the other has aged the same way, so it will be beneficial for you to change them as a pair.

How inexpensive are these do you ask? Well, at most auto parts stores, you'll be looking at spending no more than around $15-$20 each, Depending on the year, make and model of your vehicle of course. Also depending on your vehicle will be the amount of time for replacing it (them.) I recently replaced both sensors on a '98 Dodge Caravan and it took me around 15 minutes or so, and I wasn't in a huge hurry to finish, either. Again, depending on your vehicle, the location of your speed sensor(s) will vary. The Dodge Caravan's were located on the driver's side, way at the front of the transmission, allowing very easy access.

So, if you have any of the above-mentioned problems and care to tackle the problem on your own, do so before going out and buying a new instrument cluster. (Yes, I've seen many problems on here where the automotive technician was quick to replace the cluster, costing the customer hundreds of dollars, and ending up with the same problem!)

I wish you safe driving in the coming seasons and most of all, I wish you good driveability!

Kind Regards,
Jason_MKG