Hi, my car won't drive more than 10mph. Heater etc.. works fine.

Hello, you are honestly starting from the beginning basics here with diagnostic testing -- a good diagnostic tool and a sharp technician who knows what he / she is doing is needed to find out what is historically stored in the engine's processor as "failure codes". Once these codes are retrieved, testing can be performed to pin point the source of the failures. Whether or not these failures are contributing to the fact that you cannot go past 10 mph or not -- remains to be seen. Consequential damage related to the original fault could have occurred, so there could be multiple failures.