My driver side fan isn't comming on by itself. At 200* it doesn't come on and only comes on when the passenger side comes on. My understanding is that if the passenger side turns on before the drivers the ECM defaults and turns the drivers on too.

Now, why is the drivers not comming on at 220*? The only thing I can think of is that the temp sensor in the block has died?

Suggestions please.


Thanks for the help

Robert

 

thats what i would look at also.. coolant temp sensor

 

Driver side should fire off at about 222-225 deg. If it's not, swap the fan relays. The driver or primary fan can be checked simply. Jumper the ALDL connector just like you were going to get codes. In this code check mode the ECM turns on the primary fan as part of the self test. If it does not come on as I said swap the fan relays and redo the test. I would bet the primary relay is bad or intermittent. Also look at the relay socket and check for evidence of overheating of the contacts. Since the primary fan is controlled by the ECM with information detected by the CTS if it were an electronic issue related to the computer it would most likely throw an SES light. And yes, most of the ECM's will default if the secondary turns on first but give me the year and I'll check the wiring diagram to be sure.

 

Danno,

Thanks for the input. The car is an 87 IROC 305 with the dual set-up.

I'll try and swap the relays over tomorrow and let you know what happens. I'll also have a look for overheating of the contacts (what would cause this?).

Robert

 

According to Mr. Chilton in 87 only the carb 5.0 had dual fans. In the carb version the ECM does NOT control the fans, it shows two fan switches driving the fan relays. That is if they are to be believed. Still flip the relays around. If you do fix it try testing for codes and see if the primary fan runs when you do that. That will tell you if the ECM controls the primary. If they are correct in the diagram the fans will not default but you say they do. As I looked closer at your post you said BOTH fans ran when the pass side came on? That would eliminate the relay unless someone tied both fans somehow to the secondary control switch or the wiring was changed somehow. This is one of those cases where a Helms manual would help. I'll do some checking and see if I can find an accurate(and trusted)diagram for the 87.

 

Thanks Danno. I'll swap the relays round anyway and see what happens.

Robert