Ok I've been searching for days. I have a unique e-fan problem. The efan only turns on when the check engine light is on I've replaced the relay, and wired in a bypass switch and the switch doen't do anything. I've checked and rechecked the wiring for the switch. The fan does work. I can't figure it out. HELP.

Sounds like a bad coolant temp sensor.

wouldn't the switch still work?

I just swapped in a new motor and just put a new coolant temp sensor less than a weekago

Can't answer that since I don't know if you wired your switch correctly.

spliced in to the blue wire with the pink stripe, to the positive on the switch and grounded the negitive on it's own ground. I have a 1994 Cherokee sport that's all that is needed correct me if I'm wrong

Does the fan come on when you turn your air conditioning on?

no it's not kicking on at all, the only time it comes on is when the Check engine light is on, it runs constently then

The aux. fan comes on when:
A/C is Turned on.
Engine temp exceeds 213 Deg. F

The PCM completes the ground path for the Aux. Fan Relay.

Start looking at the grounds near the PCM. Loose, dirty or corroded wires/terminals should be corrected.

X2 thats what the guy tried to argue with me over in my write up...

If you unplug the coolant temp sensor the fan should run continuously. Try that and see what happens