Compressor Inlet Temp sensor
05-09-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #10
RE: Compressor Inlet Temp sensor
I also changed the coolant temp sensor and thermostat trying to narrow it down and no luck.
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05-09-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #11
RE: Compressor Inlet Temp sensor
Give us some details on the truck and engine. If it has a seperate coolant temp sender to the Cummins sensor then it may be reading high.

You will always get fault codes if the engine overheats.
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 Thanks given by: rapidisimo
05-09-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #12
RE: Compressor Inlet Temp sensor
you say the fan solenoid works how to you know it may be new but the wiring to it might be crap...the solenoid grounds to turn on fan it always has 12v + so you need to make sure the ground is good or always has 12v +


User's Signature: 2010 Lonestar - CM871 - 13sp - 3.70s - skateboarder
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 Thanks given by: rapidisimo
05-10-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #13
RE: Compressor Inlet Temp sensor
Prostar CM871. Yes I get the codes once it overheats, coolant temp high and what not. I'll chk the ground voltage tomm.
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05-10-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #14
RE: Compressor Inlet Temp sensor
(05-10-2020 )rapidisimo Wrote:  Prostar CM871. Yes I get the codes once it overheats, coolant temp high and what not. I'll chk the ground voltage tomm.

You say fan is disengauging after air builds up but never comes back on.

1. Let air build up to full pressure.

2. Have a second person Switch key off in dash (or quickly head over towards the engine fan from outside the truck as soon as you turn key off). See if fan still turns freely immediately after engine completely stops. It should still free-spin for about 10-15 seconds or so after key-off until the ecm shuts down. When the ecm shuts down about 10-15 seconds later, you will also hear the fan solenoid switch off, and the fan should now be hard to turn when the air is released from it. - By the time you get to 1 minute after the key-switch is off, the fan should now be hard to turn again because the solenoid is switched off and ecm is shut down. If it is still free-spinning a minute or more later, then the fan solenoid itself is stuck open, or the ecm itself is not shutting off properly for some given reason (bad delete programming, etc.).

3. While air is still all the way up ... turn keyswitch on without cranking. Fan should release again and be freed up.


-- This will confirm the solenoid and fan clutch are both acting normally. Should also see if there are any audible air leaking from clutch or solenoid (or rest of truck) while your at it. This can be done by run engine to build air up all the way. Shut off keyswitch, and as soon as engine comes to a complete stop, turn keyswitch back to run position. - Walk around engine compartment and truck and listen for any air leaks while keyswitch is on.

Testing it with engine running: With the air all the way up and the keyswitch in the on position, engine running ... the fan should be released and free-spinning unless the A/C or coolant temp has it switched on. Simply unplugging the connector for the enigne fan solenoid should make in engauge, and plugging it back in should release it again.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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 Thanks given by: Signature620 , rapidisimo
05-10-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #15
RE: Compressor Inlet Temp sensor
Unplug the fan solenoid with the key on, engine running, after the air is built up in the truck and the fan releases. I dont know where they are on a prostar but the majority are on the driverside fire wall. As soon as you unplug the solenoid the fan should engage. On a CM871 I believe this will throw a dash code (CEL). If it does not engage the fan then the solenoid is shot. If it doesn't do anything and/or doesn't throw a CEL then your probably looking at bad ECM or the programming.

Knowing how to diagnose things is a big time saver. So I figured I'd share why a couple of us are only thinking the solenoid is stuck open or the ecm or programming is wrong.

When the OP 1st stated that his fan is engaged when he starts the truck to build air and disengages when it gets to pressure throughout the day, that tells us that with no air the hub is locking in as it should and unlocking once air is built up. So the hub works mechanically. On a CM871 and newer, if the solenoid had bad wiring it would throw a CEL. He doesn't have one. So that eliminates most of that. So that leaves limited possibilities.

Now to narrow it down further for the OP, the reason you don't need to monitor other sensors is because you also say the truck overheats and throws check engine lights but the fan doesn't kick on. If you had said that it overheated and no lights came on you would be looking at bad programming or ECM because overheating is one of the strongest overriding codes in the engine. Once that code is triggered the engine automatically overrides everything and starts to protect itself. It turns the fan on, starts to derate (limp mode) then ultimately it'll shutdown. (If its still programmed to do so)

Being that you get a check engine light for overheating that tells us that the ECM recognizes there is a problem but the fan is not reacting. That points directly to the fan solenoid or in rare cases, crazy or wrong programming or occasionally a guy might see an ECM wire put in the wrong slot on the main plugs (this only happens when someone wrongfully rewires the harness, sometimes after engine swaps or harness replacement, but even then it should have a CEL)

What is the maximum temperature the truck gets to? Has it actually shutdown on you because it overheated?
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 Thanks given by: rapidisimo
05-10-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #16
RE: Compressor Inlet Temp sensor
I am pretty sure on that one the fan solenoid and ac compressor wires have the same plug and be switched..... double check that too. Chased my ass on a guys truck till I followed wires all the way to ecm with wiring diagram to find it wasn't hooked to the right connector up the harness.
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05-10-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #17
RE: Compressor Inlet Temp sensor
(05-10-2020 )Chamberpains Wrote:  Unplug the fan solenoid with the key on, engine running, after the air is built up in the truck and the fan releases. I dont know where they are on a prostar but the majority are on the driverside fire wall. As soon as you unplug the solenoid the fan should engage. On a CM871 I believe this will throw a dash code (CEL). If it does not engage the fan then the solenoid is shot. If it doesn't do anything and/or doesn't throw a CEL then your probably looking at bad ECM or the programming.

Knowing how to diagnose things is a big time saver. So I figured I'd share why a couple of us are only thinking the solenoid is stuck open or the ecm or programming is wrong.

When the OP 1st stated that his fan is engaged when he starts the truck to build air and disengages when it gets to pressure throughout the day, that tells us that with no air the hub is locking in as it should and unlocking once air is built up. So the hub works mechanically. On a CM871 and newer, if the solenoid had bad wiring it would throw a CEL. He doesn't have one. So that eliminates most of that. So that leaves limited possibilities.

Now to narrow it down further for the OP, the reason you don't need to monitor other sensors is because you also say the truck overheats and throws check engine lights but the fan doesn't kick on. If you had said that it overheated and no lights came on you would be looking at bad programming or ECM because overheating is one of the strongest overriding codes in the engine. Once that code is triggered the engine automatically overrides everything and starts to protect itself. It turns the fan on, starts to derate (limp mode) then ultimately it'll shutdown. (If its still programmed to do so)

Being that you get a check engine light for overheating that tells us that the ECM recognizes there is a problem but the fan is not reacting. That points directly to the fan solenoid or in rare cases, crazy or wrong programming or occasionally a guy might see an ECM wire put in the wrong slot on the main plugs (this only happens when someone wrongfully rewires the harness, sometimes after engine swaps or harness replacement, but even then it should have a CEL)

What is the maximum temperature the truck gets to? Has it actually shutdown on you because it overheated?

Yes, When the temp reaches about 230 degrees it will throw a code, warning light, then red eng light and eventually shutdown. The trk has never been deleted. The fan was working fine and then it just stopped working. A while back when I still had inside I tried to do a forced regen and it didn't finish because the eng overheated. The fan does work when I start the trk in the morning while it builds air pressure.
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05-10-2020, (Subject: Compressor Inlet Temp sensor ) 
Post: #18
RE: Compressor Inlet Temp sensor
The first time I overheated i replaced the solenoid but the issue remained. When I unplug the solenoid i do get a warning light but the fan doesn't come on and it did before.
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