I got a code 98 which reads Hard fault present, pcm in back-up mode
what to do? and what might that mean

 

I have a 1988 Ford Emissions Diagnostic manual. For code 98, it says that there is a sensor that has failed and thus the ECU is using a "alternate strategy" to keep the engine running. I would think that that means the ECU is substituting some sort of default value for the failed sensor. I don't remember if the ECU gives a fault code for all of the sensors (like maybe the engine coolant temp).

 

my f150 gave me the same code {hard fault]. with me code i checked all the connections and found my tps came unplugged some how. I hooked it back up, checked the codes again, and voila. But unfortunatly it gave me a another code telling me the tps was not responding to the test. Well good luck!

 

I got that code 98 and the 63 tps code which i through was bad before i pulled some codes

 

Just wanted to say I had Code 98 and 63 too. For about a week I had odd RPM surges while pressing in the clutch. Replacing the throttle position sensor worked wonders. Thanks for the quick fix kbolk.