We just bought a used T&C on Tuesday, and there is an issue with the speedometer. When I was going 65 mph on the highway in a my car, the wife was following with the T&C and it was registering 50 mph. At 45 mph, hers was reading 30 mph. So...we're seeing a 15 mph difference to the low side. We had no service lights on, and there were no driving issues with the van in terms of how it drove.

Needless to say, we took it to a Chrysler dealership, and while out driving it, he said the check engine light came on. He gave me some odds and ends info but said he really needed another hour or two to confirm what it was. Since we had kids, we set up another appointment for tomorrow.

When I got home, I put my reader on it and we have code P0700. There is not second code. He was hinting at replacement of the TCM, but I've also ready our issue could be the output speed sensor.

Any thoughts? Like I said, it drives fine aside from the fact that the light is on and throws a code--and the fact that the speedometer is 15 mph lower than what the actual speed is. Thanks.

 

The P0700 code is a generic transmission code. It means that there is another code stored regarding the transmission that you will need a more sophisticated scanner to get to.

The speedometer relies on the output speed sensor for a signal, but before that signal gets to the speedometer, it passes through the transmission control module, the powertrain control module, and the body control module.

The output sensor is a relatively cheap part, cheaper than the dealer would charge you to run the diagnostics. It's also a relatively easy DIY repair. The part is accessible from above. So you might want to replace that before you do anything else. If that doesn't fix the problem, then by all means get proper diagnostics done because the other parts are very expensive and you don't want to be throwing 1000's at it without knowing precisely what the problem is.