Ford Repair: Check Engine Light, o2 sensors, wire sensor

Question
Hi Chris,
I have a 1993 Cougar 8 cylinder, automatic transmission with 148,000 miles on it.  The check engine light comes on intermittently at highway speeds and then goes out.  I have a code reader and have checked for codes, but there are no codes stored.  Do you have any idea what could cause this?
Thanks,
George

Answer
Hi George thanks for asking and sorry about the delay, i have been busy.  with an intermittant chcek engine light, this is not a hard fault, the most common item  that will make a check engione light come on and off is an O2 sensor. If you can not catch it with a code reader then the sensor will have to be checked directly. There are 4 wires going into the O2 sensor. 2 whites, 1 black and one grey. With a multi meter check the black and grey wires. the voltage should flucuate from .1 to .9 volts constantly, if the voltage stays steady and any reading the the sensor is no good, repeat this step for all other O2 sensors if there are any. If it is not a 4 wire sensor then it will be a one wire sensor, The procedure is the same for checking, just the ground lead on the meter will have to go a body ground. All O2 sensors are found on the exhaust system.
good luck
Chris P