Hyundai Repair: replaced engine problems, 2004 hyundai sonata, heater hoses

Question
Hello. I have a 2004 Hyundai Sonata that recently had a new (used) engine put in. Since it was put in, the speedometer doesn't work. Then the next day the AC stopped blowing cold air and the next day after that, it started having trouble going into gear smoothly. For example, a jerking when you put it in reverse.  A check of the codes says there is a problem with the computer. I guess it's either bad or not communicating properly. Could this be something not hooked up correctly?

Answer
Hi, Ann.  I'm going to address the problems one at a time.  Some are more likely related to the replacement and others are less likely related.

1.  The speedometer reading is based on input from the speed sensor on top of the transmission.  It's possible this sensor was disconnected for the engine replacement and not reconnected afterward.  It's also positioned in such a way that if it's unplugged and the heater hoses are removed, the coolant tends to run directly onto the sensor.  If left there when the sensor is reconnected, it can short the sensor circuits together, blowing the fuse and/or preventing the sensor from working properly.

2.  In most cases during an engine replacement, the a/c system will be evacuated so that the hoses can be disconnected and then recharged again once the job is complete.  It's possible that one of the o-rings where the hoses were disconnected and reattached was cut during the reattachment.  It's also possible that an a/c line wasn't routed properly on installation of the engine, causing it to rub through on a moving component.  Yet another possibility is that there's a problem with your engine overheating, in which case the ECM will command the a/c off.

3.  If the motor mounts were not bolted into place properly, this could cause a jerking when reverse or drive is engaged, as well as during shifts from first to second, etc. while driving.  This could also be potentially related to the speed sensor issue and the diagnostic trouble code(s) you've retrieved.

4.  I'll need more information on the trouble codes you've retrieved.  If you can give me the code number itself, I can translate what the code means.  While there are codes that indicate computer problems, occurrences of these are very rare.  Most frequently when I'm told a code indicates a problem with the computer, the trouble code is being misinterpreted.