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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8412
Experience:  I am ASE Master Truck Certified.
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I have a 1996 cat engine 5ek51876 3406e engine fan does not turn on @ hig temp.ECM is

Customer Question

HI I have a 1996 cat engine 5ek51876 3406e engine fan does not turn on @ hig temp.ECM is on. no signal from ecm to fan solenoid.Wand works with a/c on and manual switch. high temp blew head gasket can fix head gasket cant fix fan problem can you help. Thanks JIM.
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.
Hey Jim. Thanks for asking your question and requesting me. I will try and help you out.To turn the fan on, ECM will remove power from pin 28 that powers the fan solenoid.How high is the temp getting on the engine?
Customer: replied 1 year ago.
temp high 210 to 220
Customer: replied 1 year ago.
there is no power going to solenoid traced wire can wire have break in told that its hard wiered in
Expert:  Cat Man replied 1 year ago.
Thanks for the information. Yeah that is to high. The fan should be on at that temp. Since it is not, I would check power from pin 28. If you have no power, the ECM wants the fan on. I would then suspect a faulty fan relay or fan solenoid. Please reply back if you need more help or have more questions. I am happy to assist.
Expert:  Cat Man replied 1 year ago.
Does it take power to turn the fan on? If so you have one of two things causing your problem. The first is a failed relay. If you trace pin 28 you should find the relay. Second is a faulty ECM. It's rare for ECM's to fail and cause this but it's possible
Customer: replied 1 year ago.
where is the re lay located plus I was told by pete there is no relay can you call me an talk I wll pay for your time(###) ###-####
Customer: replied 1 year ago.
I already have to replace head gasket but need fan to work
Expert:  Cat Man replied 1 year ago.
If the fan control solenoid needs power to engage the fan. There must be a relay. The reason I say this is because the engine ECM removes power to turn on the fan. Whenever the fan needs power to turn on, a nornally closed relay must be installed. That way when the ECM removes power the fan comes on. You should be able to follow the pin 28 wire or the fan solenois and it lead you to the relay. Could be on the fire wall or frame rail
Customer: replied 1 year ago.
looked at wire diagram shos no relay it is hard wired in only relay is low fan relay solenoid is new
Customer: replied 1 year ago.
its a shame I have this problem engine only has 75000 miles on rebuild already blew head gasket
Customer: replied 1 year ago.
can you send pics of wiring to me
Expert:  Cat Man replied 1 year ago.
Thanks for the information. If there is no relay then the fan should come on with no power. Like I was saying. Cats strategy to control the fan is no power from pin 28 to turn on fan. When the ECM wants the fan off, it will put power on pin 28 Is there no power to the fan solenoid? And it's off? Have you tried putting power to it to turn it on?
Customer: replied 1 year ago.
yes I have but something is not right I understand how it all works ecm is on in fan mode 28 check out okay fan works in override
Expert:  Cat Man replied 1 year ago.
So putting power to it turns the fan on?
Customer: replied 1 year ago.
when I strat the engine fan turns on then cuts out that is normal
Expert:  Cat Man replied 1 year ago.
Yes that is normal. The fan should come on everytime the engine is started. Then go off.Can you tell me if you have put power to the fan to turn it on?
Customer: replied 1 year ago.
at high idle standing temp rising still no fan fan will cycle with a/c on fan will turn on in override .
Expert:  Cat Man replied 1 year ago.
If the fan comes on when you start. I am beginning to think your temp gauge is reading wrong. Does the red engine warning light come on when the temp gets up to 220?
Customer: replied 1 year ago.
I can fax you the bill and work peterbilt did they even tried a test ecm
Customer: replied 1 year ago.
yes red light and warning buzzer
Expert:  Cat Man replied 1 year ago.
Does the red engine warning light come on when the temp is at 220? Were there any codes for high coolant temp?
Expert:  Cat Man replied 1 year ago.
Thanks for the information. Can you tell me if putting power to the fan solenoid turns the fan on? OR does unplugging the fan solenoid turn the fan on?
Customer: replied 1 year ago.
I turn on override engine cools light goes out
Customer: replied 1 year ago.
have to power fan solenoid to turn on
Customer: replied 1 year ago.
why does fan engage when I shut the engine off
Customer: replied 1 year ago.
fan should always spin freely when engine is off
Customer: replied 1 year ago.
can solenoid have to powered to the ground side just a thought
Expert:  Cat Man replied 1 year ago.
Thanks for the information.It is normal for the fan to engage when the engine is off.IF it takes power to engage the fan, there is a relay somewhere. I am positive. The reason is if it takes power to engage the fan, the ECM sends power to turn the fan off. Since it works with the fan override. The problem must be a relay. I will get you a diagram.
Expert:  Cat Man replied 1 year ago.
Here is a diagram of the wiring.https://www.dropbox.com/s/cmra01zqzvhisl9/5EKfan.jpg?dl=0
Expert:  Cat Man replied 1 year ago.
Hey.
I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks!