Radiator Fan Circuit

[NJMarc]

It seems like the Radiator Fan Relay signal wire coming from the Logic Module to my Relay is not responding. I tested the circuit for continuity and resistance from the plug at the relay, to the pinout on the red connector - its fine. Is my logic module the problem? This is on a 1985 GLH Turbo, T1, bone stock.

I swapped 2 different relays, one new one used, no dice. However, if you open one up - and manually push it down, the fan powers right up, so I know the fan is operative and getting juice.

[Qualt PPK]

Logic Module gets OK from coolant temperature sensor and then ground the fan rely. It could be temperature sensor or Logic Module. If you ground the wire which you tested, it will pull
the rely witout to press it manualy.

[NJMarc]

ok, checkin that tommorow...

Hmmm, come to think of it, the car started when I had accidentially left the coolant temp sensor unplugged overnight, is this a sign it may be that?

Also I noticed that when I did unplug it, the car reacted similarly when everything is normal - kinda dipped in rpm's somewhat.

On another note, my boost is funny now, whenever I go into boost, the car stutters, runs like crap - but only in boost...isnt the coolant temp sensor related to this?

[NJMarc]

but wait - shouldnt the fan turn on anyway if the coolant temp sensor is bad and unplugged? Now im wondering if that wire is the culprit - broken somewhere...

[NJMarc]

Checked the Coolant Temp Sensor with a DRBII. Repsonsive, and it goes to 5.00v when you unplug it. I now have a Code 35 - Radiator Fan Relay. I think the driver on my LM is toasted. Time to try a LM.

[Abkshelby]

Sounds as though your coolant temp sensor isn't happy. It sends the signal to the logic module which cuts on the fan at 210 degrees. It will give you a fault code if the sensor is bad. The engine will also run rich and usually bad when this sensor goes. Your running in limp in mode if this sensor is bad or unplugged. This will screw up your boost levels. And yes when you unplug the sensor the cooling fan will cut on. You will need to unplug the upper power module connector for 30 seconds to reset your logic module. Hope this helps.

[NJMarc]

if its bad though - it should turn the fan on anyway when its unplugged, correct? Funny you say that cause I do have sudden boost issues.

I'm thinking bad coolant temp sensor, and logic module now.

I think the Radiator Fan Relay signal circuit is no good in the module.

[Abkshelby]

The cooling fan will cut on when the coolant temp sensor is
unplugged, ALWAYS. If it does not the problem is either the
wiring to the relay or the logic module may have an issue.
On the '86 GLHS I used to own I had a similar problem with
the cooling fan. Turned out to be the connector to the relay
had a loose terminal that wasn't making contact on the relay.
You can test the circuit with a DRB. Go to the sensor test mode
or the actuator test mode (Can't remember haven't recovered
from SDAC-13 yet) and test the relay. The logic module very
seldom will go bad in this area. The charging circuit normally
goes bad on L-bodies. But anything is possible. Keep us updated.

[NJMarc]

I did an actuator test - nothing.

[NJMarc]

Hey Alan, was that you I was eating dinner with at the SDAC dinner, you had you're CSX with black crabs at the show?

[Abkshelby]

Yes it's me. Unfortunately the CSX was slightly wounded on the return trip home. A muffler laying in the road was flung up into the car. I was able to swerve enough to keep it from going under the car but it smashed into my left side skirt taking a chunk out of it. It ripped the whole skirt loose from the car. Luckily it is repairable though. So much for having all original paint.
So your cooling fan won't cut on when you unplug the coolant temp sensor huh? HMMM. Now I'm starting to wonder if the LM is bad. In the actuator mode with the DRB if your not getting a signal to the relay then the only other thing would be to try another LM. My only other guess would be if the AC relay on the other fenderwell is screwed up. Can't remember if your car had AC. An open circuit in this relay can cause a problem with your fan relay if I remember correctly. You can check the AC relay with the DRB also. PM me or email me if need be."thumbs up

[NJMarc]

The car does not have a/c but DOES have complete a/c wiring. Can I simply unplug this relay and see what happens?

[rpeatt]

Ok, this is exactly what happened to my car.

The relay is fine, the coolant temp sensor is fine, I've tried two LMs, the wiring between the relays and the fan is fine. Soo.... it must be the relay between the relay and the logic module. Is there a fusible link in there somewhere?