What would make an OBDII not recognize that the code reader is attached?

Question

This is a 2002 Ford Escort ZX2. Engine light came on but would not recognize the reader connection. Next day or so, the speedometer stopped working but all other gauges are OK. Just replaced speedometer cluster with another one with no change. What could be wrong for the OBD to fail?

Answer 1

Power to the scan tool. Most of the time when a scan tool can not read a vehicle but can read other vehicle this mean power to the scan tool is not there, You need to find the cigarrette lighter fuse or auxillary fuse, this is what also powers the OBD connection

Comments

It doesn't matter if pin 16 has no power the scan tool will not read, the fuse is located in the engine junction fuse box listed as OBDII it is a 10amp fuse.

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Sorry, I totally misread your first response.  Fuse is fine, was replaced anyway.  Afraid it's the PCM.