Engine fan wont turn off

[davidjurss]

Having a bit of an issue here lately, and I'm tired of just throwing parts at it. I have an 06 CM870 that the engine fan has stayed on and wont turn off. I went after the usual suspects, like the air solenoid and ac high pressure switch to no avail. I've even replaced the dash switch, with no results. The fan will free spin when the truck is started, but something is commanding the solenoid to release air and start the fan, so I'm fairly certain the fan hub itself is still good. I dont have Insite yet, so I can't check to see what's going on internally, but so far it hasn't kicked on a check engine light. Any help would be appreciated, since this is killing my fuel mileage and with a Peterbilt 379, I need all I can get! Thanks!

[Nilao]

Where are you located? Maybe someone close by has insite and can look at it.

[davidjurss]

I'm on my way to Florida at the moment, but live south of San Antonio

[Lonestar10]

I believe there is 2 temp sensors for coolant one may be bad or has bad connection/wiring. I believe the intake temp sensor can also turn fan on I know my 871 does when at low speed and high boost causing high intake air temp

[Rawze]

870's also have a bug in them for engine fan below a certian ambient air temp. if the ambient air temp is reading crazy cold(extreme cold weather or bad sensor), the engine fan will stay on too.

just throwing that out there if other things do not check out.

[davidjurss]

(03-09-2020 )Rawze Wrote:  870's also have a bug in them for engine fan below a certian ambient air temp. if the ambient air temp is reading crazy cold(extreme cold weather or bad sensor), the engine fan will stay on too.

just throwing that out there if other things do not check out.

Just happens that the ambient temp was in the teens when it started. Maybe one of the temp sensors is stuck.

[davidjurss]

(03-09-2020 )Lonestar10 Wrote:  I believe there is 2 temp sensors for coolant one may be bad or has bad connection/wiring. I believe the intake temp sensor can also turn fan on I know my 871 does when at low speed and high boost causing high intake air temp

Any idea where those might be? I see what looks like one in the thermostat housing, not sure if that's one of them or not.

[Chamberpains]

You're blindly throwing parts at it. That is a waste of money. Stop stop stop stop. Go somewhere that has Insite or get Insite yourself and diagnose it properly.

After you throw hundreds of dollars in sensors at this truck you could of had it looked at and find which sensor is reading wrong. Properly troubleshoot that sensor and circuit and find out it the wiring all along.

Also, is this EGR still operational? If not was the programming done from someone from this site? If not, this could be your problem along with many others that you have no idea of.

[05ISX450]

(03-09-2020 )davidjurss Wrote:  Having a bit of an issue here lately, and I'm tired of just throwing parts at it. I have an 06 CM870 that the engine fan has stayed on and wont turn off. I went after the usual suspects, like the air solenoid and ac high pressure switch to no avail. I've even replaced the dash switch, with no results. The fan will free spin when the truck is started, but something is commanding the solenoid to release air and start the fan, so I'm fairly certain the fan hub itself is still good. I dont have Insite yet, so I can't check to see what's going on internally, but so far it hasn't kicked on a check engine light. Any help would be appreciated, since this is killing my fuel mileage and with a Peterbilt 379, I need all I can get! Thanks!

Does anyone know how much amperage goes to the air solenoid? I was told my ECM is not sending the correct amperage to it . Wonder if I could use an electronic thermostatic control. Has anyone ever tried this?