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2005 aux fan stays on
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=87544		 Page 1 of 1
Author:  ADVGabe [ Thu Dec 14, 2017 4:24 pm ]
Post subject:  2005 aux fan stays on
Hey all,
I tried to search and got nothing. used google search and read several threads but got nothing useful.

2005 CRD, just put the engine back together (tbelt and rockers) and now the electric aux fan always runs when the engine runs.

If I pull the relays I can hear/see the fan slow, with one relay, and stop with both relays.

I disconnected both sensors on the AC lines that I could see and neither did anything to affect the fan.

The AC switch does not seem to do anything, light in the switch comes on but I cannot tell if the compressor is cycling or not thanks to the noise of the fans.

The dash temp gauge appears to work fine, and as best as I can tell that is the only sensor on the 2.8LTD? contrary to the gassers which might have two?

I wiggled the wiring bundle behind the fuel filter head and got no response from the fan.

The wiring schematic is not very helpful as it only shows the two relays and the ECM.

Can anybody shed light on this? pretty please? :?
Author:  Sir Sam [ Thu Dec 14, 2017 7:49 pm ]
Post subject:  Re: 2005 aux fan stays on
IIRC if you connect the sensors on the AC line it causes the sensor to read high pressure, which would trigger the fan to run.

I see you unplugged the relays but have you verified they are switch on and off? It is possible for a relay to stick in the on position, especially one with a high current draw.

The AC fan is controlled by the ECU, not by only a relay setup with on/off pressure switches or temp switches.
Author:  ADVGabe [ Sat Dec 16, 2017 6:55 pm ]
Post subject:  Re: 2005 aux fan stays on
Correct, the ECU triggers the fan. I verified that on the factory wiring diagrams: no fancy PWM fans here.
We tested the relays, they are functioning correctly.
using two different mobile aps and a bluetooth ODB reader the intake air temp reading looks logical.

The only time we got the fan to behave differently is when we have the TMAP and airbox temp sensors disconnected, the fan would come on with the key. Whereas up till this point the fan would only come on shortly after engine startup.

To me this verifies that the wiring ECU>Relays>Fan are OK, and that the ECU is either freaking out or a sensor is bad somewhere.

Disconnecting both of the plugs on the AC lines had no effect on the fan operation while running.
Author:  ADVGabe [ Sat Dec 16, 2017 8:50 pm ]
Post subject:  Re: 2005 aux fan stays on
Another thing noted today was that the two fan relays click, but it also sounds like one of the serp. belt pulleys are being triggered at the same time...

will have to investigate that a little more.

If only we had the logic diagrams for a 12+ year old Bosch ECU this wouldn't be a problem.
Author:  flash7210 [ Sat Dec 16, 2017 11:06 pm ]
Post subject:  Re: 2005 aux fan stays on
Is the AC clutch engaged? That will definitely change the sound of the pulleys.
If the AC is on then the electric fan will turn on.

The electric fan adds additional load to the alternator which could change the sound of the pulleys.
Author:  WWDiesel [ Sun Dec 17, 2017 10:47 am ]
Post subject:  Re: 2005 aux fan stays on
The only two serpentine pulleys that can trigger electrically are the AC compressor clutch and the viscous heater clutch. You should be able to look at the front of the pulley while the engine is running and observe whether either of the aforementioned pulleys are rotating or setting still.
The relay for the viscous cabin heater can be removed to eliminate it!
You can also remove the relay for the AC compressor clutch to eliminate it!

Both relays are located in the Power Distribution Center under the hood in front of the battery!
See diagram for locations:

Image
Author:  ADVGabe [ Mon Dec 18, 2017 7:26 pm ]
Post subject:  Re: 2005 aux fan stays on
WWDiesel wrote:
The only two serpentine pulleys that can trigger electrically are the AC compressor clutch and the viscous heater clutch. You should be able to look at the front of the pulley while the engine is running and observe whether either of the aforementioned pulleys are rotating or setting still.
The relay for the viscous cabin heater can be removed to eliminate it!
You can also remove the relay for the AC compressor clutch to eliminate it!


Good thinking WW. I wasn't sure about the relevance of checking the clutch engagement, but now I am glad I did:

The AC compressor is not engaging.
This makes me think one of the AC sensors is bad/malfunctioning and triggering the fan via the ECU. Now to figure out how to test this theory...
Author:  flash7210 [ Mon Dec 18, 2017 8:22 pm ]
Post subject:  Re: 2005 aux fan stays on
Maybe it’s a bad coolant temperature sensor.

There are only two things that cause the electric fan to turn on.
Air conditioning being turned on. (AC pressure)
High coolant temperature.

I would think that if it were the coolant temperature sensor you would notice the temp gauge being higher than normal.
Author:  WWDiesel [ Mon Dec 18, 2017 8:23 pm ]
Post subject:  Re: 2005 aux fan stays on
ADVGabe wrote:
WWDiesel wrote:
The only two serpentine pulleys that can trigger electrically are the AC compressor clutch and the viscous heater clutch. You should be able to look at the front of the pulley while the engine is running and observe whether either of the aforementioned pulleys are rotating or setting still.
The relay for the viscous cabin heater can be removed to eliminate it!
You can also remove the relay for the AC compressor clutch to eliminate it!


Good thinking WW. I wasn't sure about the relevance of checking the clutch engagement, but now I am glad I did:

The AC compressor is not engaging.
This makes me think one of the AC sensors is bad/malfunctioning and triggering the fan via the ECU. Now to figure out how to test this theory...

Maybe unplugging them one at a time and see what happens? :roll:
Author:  ADVGabe [ Mon Dec 18, 2017 8:38 pm ]
Post subject:  Re: 2005 aux fan stays on
Ok another update:

The AC clutch fuse checks out okay, and swapped with another 20A.
AC clutch relay I did not check, but did swap with the viscous clutch relay and it functions OK.

Interestingly on the switch side of the relay socket I get one pin with battery power, and the other pin has ~3.5V. :(
On the viscous clutch switch side I get battery power and 0.1V, which is what i would expect on the AC relay.
Not the end of the world, as I dont yet know what it should be seeing when switched on.

Still need to figure out how to either test the pressure sensor, and/or trick the ECU/FCM into thinking its okay and tripping the compressor relay on its own....
Author:  ADVGabe [ Mon Dec 18, 2017 8:42 pm ]
Post subject:  Re: 2005 aux fan stays on
WWDiesel wrote:
Maybe unplugging them one at a time and see what happens? :roll:


Did that. No change in the Aux fan sadly.
Author:  ADVGabe [ Mon Dec 18, 2017 8:45 pm ]
Post subject:  Re: 2005 aux fan stays on
flash7210 wrote:
Maybe it’s a bad coolant temperature sensor.

There are only two things that cause the electric fan to turn on.
Air conditioning being turned on. (AC pressure)
High coolant temperature.

I would think that if it were the coolant temperature sensor you would notice the temp gauge being higher than normal.


That was my first thought as well BUT:
Gauge appears to be normal.
temp checked via OBD2 reader checks out as well.

Only one ECT sensor on the engine that I can find, despite some forums goons claims to there being 2. manual backs me up as best as I can tell.
Author:  flash7210 [ Mon Dec 18, 2017 8:51 pm ]
Post subject:  Re: 2005 aux fan stays on
Correct. Only one coolant temperature sensor.

You must have a short to ground somewhere.
Author:  ADVGabe [ Mon Dec 18, 2017 10:41 pm ]
Post subject:  Re: 2005 aux fan stays on
flash7210 wrote:
You must have a short to ground somewhere.


Im not so sure. Im going to test the AC system/switches before I start unwinding a wiring harness. :)
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