Hello there, I have recently signed up and searched for an answer for the error code:P0691 I have on my Street Rod. I know it's related to the cooling fan relay but here's the things I did before I had this code.
My battery died and I tried to jump start via battery tender input plug which is just under the seat. The problem is (please don't laugh) I tried to power up the battery through this input by connecting the cables to my car's battery. As you can assume battery did not power up. Later I figured out how to properly jump start the battery correctly and I successfully got the bike runing without problems. My mechanic said that those relays and circuit breakers are only capable of handling 1 to 2 amps while I tried 100 amps to get through. So I am sure some circuit breaker or relays went off because I tried to charge it through battery tender input.
After I got the bike runinng, I had 3 error codes; U0156 - U0001 - P0691. U0156 - U0001 are gone but P0691 remains.
Do you think I can ride it or I should worry about it?

 

The PCM controls the cooling fans by sending a ground signal to the cooling fan relay. The voltage on the signal circuit is high, around battery voltage, when not commanded on (not grounded). The opposite is true when commanded on (grounded), the voltage is somewhere near zero. DTC P0691 is set when the PCM senses the voltage low when the cooling fan 1 is off.

motors are turned on and off by the powertrain control module (PCM) according to the readings from the engine coolant temperature sensor

switch relay, if that doesn't do anything and wiring is good then maybe the control unit.
however, that circuit should not have been activated since the engine was cold unless they briefly power up on power on testing.

 

Ok I have solved the problem. It seems it was about the cooling fan 15A fuse which is located underneath the seat. Was quite easy for me to fix this problem and I have no trouble codes now. I just followed the owner's manual after detecting the problem.