Hey Guys, my much loved, but much maligned (by others) '97 XJ i6 4x4 is overheating and I have discovered that the aux fan is the/a cause.

Issue is this:

When I put a relay on the cooling fan terminals in the ecu, when the fan is supposed to be on (ie, ac is on or temp is high), the fan kicks on for a moment, then stops. It can jiggle the relay around sometimes to get it to kick on for a split second.

Fan does not stay on with relay fully seated. There is an audible click when all four terminals/posts are first connected (like an electrical click at the relay), the fan comes on, then goes off.

If I jump the power lines for the fan, it engages and stays on.

Any ideas where to troubleshoot this thing? Is it possible there is incorrect voltage going to the signal side of the relay that causes it to engage and then shut off?

 

I notice that the fan comes on for that split second, even if the AC is off and car is cold...

Voltage shows ~12.5 volts on signal and power side.

 

Swap the relay with another like it in the PDC. There are a few that are the same relay.

If it works then, replace the relay.

 

Thanks Mark, I tried a few relays and they all have the same behavior, they works for split second and then the fan stops.

 

If when you jiggle the relay and it turns the fan on and you eliminated the relay itself by swapping, i'd first look closely at the relay socket contacts for spread pins or corrosion.

 

^^ That plus make sure none of the contacts are pushed down in the socket.

 

Thanks guys, I actually removed the wire terminals from the plastic hard shell and stuck them directly onto the relay(s), to eliminate things sliding around.

What happens is, I'll have three connected, and when I put the forth on, the fan kicks on for a second, and then stops, even though the forth wire is now connected solidly.

This happens with any of the four wires being the last to go on...

 

Sounds like one is not making a good connection .Wiggle them one at a time trying not to disturb others. Maybe connector on wire is bad.

 

Does anyone have/know where to find a good wiring diagram for the aux fan operation?

 

Have you checked witch wire is loosing power or ground or the trigger ?

 

Actually, a friend just helped me figure out that the problem is on the signal ground wire. A test light shows the same behavior as the fan (ie, it flashes for a split second and goes off when connected).

So, I think a quick fix of connecting the signal ground on the relay to a new ground point is doable... but I'd really like to figure out the root cause.

Also, I've noticed that the fan is ALWAYS ON now, if the key is ON. (This is with the signal ground being manually connected.) Anybody have a thought on why that would be?

 

If the signal is a ground that should come from your computer . you can check the wiring at the computer making sure the all computer plugs are clean and tight . if they are all good your computer could be going bad .

 

Ugh, I hope not the computer, it was replaced about 1.5 years ago.

I'll check the wire at the computer, thanks.

 

Well yeah if i understand what you're doing correctly.
By manually grounding the relay's coil's PCM terminal you're bypassing the PCM's relay energizing ground signal as you call it, causing the relay to energize permanently as long as you manually ground it.

Do you have AC? If so is it working?

 

Try Unhooking new ground and unplug cts on thermostat housing does fan stay on when running now ?