Electric Fan Issues

[menos]

Long story short.

My electric fan is not kicking on by itself. The previous owner of the jeep had wired in a switch that grounded the fan relay thus turning the fan on.

I've been trying to track it down and it looks like the computer is not activating the fan. Pin 31 on the ECM never goes to ground.

How should I go about testing the circuits for the a/c and the temp, so I can be sure the computer is receiving the correct signals?

 

[Jess]

does the fan not come on when the ac is on, or just when it gets over 210? why don't you just use the manual switch?

 

[trouttrooper]

With the engine off unplug the temp sending unit on the thermostat housing, then start the engine. After it's initial start-up diagnostic the e-fan should turn on (btw the check engine light will come on but after you turn the engine off and re-plug the connection it will turn off). That will at least tell you if the electronics are working properly (assuming the switch the previous owner put in isn't messing things up or you don't have a bad temp sending unit).

 

[88-xj-laredo]

I am having the same problem with my 88, the last owner put in a manual switch but it has never come except one time, I forgot to write down the temperature but the fan came on, and the switch would turn it on and off, but now and before I can never get it to come on. It sounds like the same problem your having... and I still haven't been able to track it down.

 

[sjx40250]

menos has a 91 and is different than the 88. My 90 has had the same problem for years. I thought it was the temp sensor in the rad (same as 88 but not 91) and replaced it. Still did not work. Never did find out why it doesn't work. I bought a kit that added a sensor in the t housing and wired it in and now the fan runs when the temp is over 190, even with the engine off. I don't loose battery power either and all my over heating problems are gone. Did this about 7 years or more ago.

 

[rag]

menos has a 91 and is different than the 88. My 90 has had the same problem for years. I thought it was the temp sensor in the rad (same as 88 but not 91) and replaced it. Still did not work. Never did find out why it doesn't work. I bought a kit that added a sensor in the t housing and wired it in and now the fan runs when the temp is over 190, even with the engine off. I don't loose battery power either and all my over heating problems are gone. Did this about 7 years or more ago.

any info/links on this kit?

im curious

 

[langer1]

91 and up there are two temp sensors.
1. is for the gauge only, 1 is for engine control only.

The one for the gauge can be off and reading falsely high, or the one for engine control can be reading to low.

Most often it's a sensor problem, not a ECU problem.

 

[GrimmJeeper]

any info/links on this kit?

im curious

you can get em at any parts store, they might have to order it for you. people usually put em on hotrods that have been converted to elec fans.

 

[Alacran]

You should have power at your Fan Relay at P.D.C on wires DB/WT & LG/RD coming from fuses # 15 & 18 ( P.D.C ) also...P.C.M provides ground to the relay at temperatures above normal ( 180 Degrees ) through wire DB/PK....
Bypass P.C.M ground circuit at relay in P.D.C and see if the fan turns ON...If fan turns on at temp. above 180 Degrees , repair open to ground circuit ...If fan does not turn ON , you probably have a bad Fan Motor....

 

[88-xj-laredo]

you can get em at any parts store, they might have to order it for you. people usually put em on hotrods that have been converted to elec fans.

So what should I ask for at the parts store, a kit that adds a temp sensor into the t housing?
:dunno:
I think I might try it, would it matter that I converted my closed system to an open system?

 

[menos]

You should have power at your Fan Relay at P.D.C on wires DB/WT & LG/RD coming from fuses # 15 & 18 ( P.D.C ) also...P.C.M provides ground to the relay at temperatures above normal ( 180 Degrees ) through wire DB/PK....
Bypass P.C.M ground circuit at relay in P.D.C and see if the fan turns ON...If fan turns on at temp. above 180 Degrees , repair open to ground circuit ...If fan does not turn ON , you probably have a bad Fan Motor....

As I stated earlier, the fan and relay work just fine if you apply a ground to the relay. For some reason the PCM is never setting pin 31 to ground. I've tried disconnecting the sensor (while the engine was running) and that didn't due it either. It threw a check engine light but it never set pin 31 to ground.