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Where is the coolant temp sensor?

X

XJFever

NAXJA Forum User
Location
Anchorage, Alaska
its a 1990 Cherokee. On my newer one its right there on the water pump. On this one, I thought it was on the lower part of the radiator, but that turned out to be the fan sensor.

Basically, I'm trying to figure out why my electric fan wont turn on. I replaced the fan sensor and it didn't help. After I put the new fan sensor in, I took it for a drive. The temperature gauge would not even give me a reading-it stayed at 0, then would jump all the way up, then go back down to 0.

I'm thinking it would be the coolant temp sensor I have to replace. Is it located right there on the intake manifold? It looks the same as the new one I bought, but someone told me that was the air temp sensor.

pics of where it is would definitely help. thanks...
 
Coolant temp sensor should be on the head, I think, near the rear, and below the intake manifold. Look for a sensor screwed directly into the side of the head. Be careful, because it's really easy to shear off if it's rusted in. The one in the manifold itself is the intake air temp sensor.
 
On your 1990, you have three:

Thermal Fan Switch - Driver's side radiator tank.
Gage/Warning Lamp Sensor - Driver's side rear of the cylinder head.
ECU Sensor - Driver's side of the cylinder block, behind the exhaust manifold

If your e-fan isn't turning on, it's generally one of two causes:

1) The TFS has failed, and wants replacing.
2) The relay (driver's side fender liner, near front) has failed, and wants replacing.

The relay is a standard DIN relay, available anywhere for ~$10. They're used all over - so you may as well get a small handful and keep them in the spares with your fuses and bulbs (the fuel pump uses one, the A/C clutch uses one, the HEGO heater uses one - and you may as well use the same thing when you're adding lamps and such anyhow. Keeps things easy...)

If it was working before and isn't now, those are the first two things I'd check - assuming there's nothing obviously wrong with the wiring for some reason (impact to driver's front wing, mechanical damage to driver's fron engine bay, ...)
 
ok...update

found the coolant sensor and replaced that. the fan still wont turn on. i hooked up an external battery to it and it worked fine. the thermal fan switch was also replaced. so im thinking maybe the relay. is it the one right in the corner where the wire to the fan is?

also, found out why i wasn't getting the reading at all before--it was the ecu sensor which was unplugged.
 
5-90 said:
If your e-fan isn't turning on, it's generally one of two causes:

1) The TFS has failed, and wants replacing.
2) The relay (driver's side fender liner, near front) has failed, and wants replacing.
Click to expand...

My e-fan isn't coming on when I use the defogger or the A/C. I have read that if the A/C system isn't charged, the e-fan won't kick in with the defogger on. Is this true?
 
XJFever said:
also, found out why i wasn't getting the reading at all before--it was the ecu sensor which was unplugged.
Click to expand...


the sensor on the back of the head is for the gauge, the one that provides the ecu with a signal is on the side of the block.
 
So, i'm having trouble figuring out why the fan won't come on. I changed the relay and it still doesn't come on (assuming i changed the right one-to the right of the EGR solenoid). The fan switch sensor and the coolant temp sensor were replaced. What else should i look for?
 
XJFever said:
So, i'm having trouble figuring out why the fan won't come on. I changed the relay and it still doesn't come on (assuming i changed the right one-to the right of the EGR solenoid). The fan switch sensor and the coolant temp sensor were replaced. What else should i look for?
Click to expand...

A wiring fault. Time to crawl through our fan wiring and see if anything has happened to it...
 
Quoted from this site: http://jeephorizons.com/phpbb/viewtopic.php?p=71583#71583

3) Disconnect fan relay connector. Fan relay is located on
left inner fender panel. Using a jumper wire with an in-line 25-amp
fuse, supply battery voltage to fan relay connector terminal No. 4.
4) If fan operates, motor is okay. Go to next step. If fan
motor does not operate, check continuity between fan relay connector
terminal No. 4 and body ground connections. If continuity exists,
replace fan motor. If continuity does not exist, repair open and
retest.
5) Disconnect fan relay connector. Turn ignition switch to
the "RUN" position. Check continuity between fan relay connector
terminal No. 5 and body ground connections. If continuity does not
exist, repair open circuit. If continuity exists, go to next step.
6) Using a jumper wire with an in-line 25-amp fuse, jump
across fan relay connector terminals No. 1 and No. 4. If fan motor
operates, go to next step. If fan motor does not operate, repair fan
relay fuse link.
7) Check for battery voltage at fan relay connector terminal
No. 2. Connect a jumper wire across radiator temperature switch
connector. Radiator temperature switch is located on radiator outlet
tank, above lower radiator hose. If fan does not operate, replace
radiator temperature switch. If fan operates, go to next step.
icon_cool.gif
Check for battery voltage at fan relay connector terminal
No. 2. If battery voltage is not present, replace fan diode assembly.
Click to expand...


How do you know what terminal numbers are which on the relay terminal? anyone know?
 
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