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ambient temperature sensor?
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=86702		 Page 1 of 1
Author:  flash7210 [ Sat Jun 10, 2017 7:48 pm ]
Post subject:  ambient temperature sensor?
What is the purpose of the ambient temp sonsor?

I've unplugged it. It set a code.
But no noticable change in performance.

So why would the ECM need to know what ambient temp is?
Author:  GordnadoCRD [ Sat Jun 10, 2017 8:20 pm ]
Post subject:  Re: ambient temperature sensor?
My guess is the part of the program that figures air density. It also has ambient pressure sensor (psia), I assume, for the same reason.
Author:  mass-hole [ Sat Jun 10, 2017 11:05 pm ]
Post subject:  ambient temperature sensor?
I thought the Ecu utilized its internal barometric sensor for all tuning needs. Also, as far as I know, the Ecu does not care about temp when calculating fueling, only MAP. There is one table In the tune which either limits boost based on IAT or I suppose it could adjust the effective boost the Ecu uses for fueling based on MAP and IAT(hotter air is like having less boost) but still is not utilizing the air box sensor.
Author:  GordnadoCRD [ Sun Jun 11, 2017 3:14 am ]
Post subject:  Re: ambient temperature sensor?
Isn't Ambient Temp Sensor the one on the grille support?
Also, I wasn't stating that the psia data comes from the sensor, just that when the scanner is registering live data, that is one of the things it tracks. For what purpose, I'm not certain. I suppose Ambient Temp sensor could be one of the sensors used for Glow Plug operation, or maybe just the EVIC readout?
Author:  flash7210 [ Sun Jun 11, 2017 7:23 am ]
Post subject:  Re: ambient temperature sensor?
Ambient temp sensor is in the grille.
Inlet pressure sensor is in the air filter box lid.
Ambient pressure sensor is supposedly in the ECM. (I cannot confirm this)

We already know that a unplugged inlet pressure sensor will cause some performance issues.
In the past, a few have reported problems with the ambient pressure sensor. But I don't know what issues that fault caused.

If the ambient temp sensor is only for the EVIC, why would it set a code on my 05 Sport that doesn't have a EVIC?

It would seem to me that all the ECM needs to see is IAT and MAP.
Ambient readings don't mean anything when you have a turbo.
What matters is what's actually going into the engine.

And I'm pretty sure Yeti confirmed that the coolant temp sensor is used for glow plug management. (i.e. unplug the coolant temp sensor for maximum glow plug duration)
Author:  WWDiesel [ Sun Jun 11, 2017 7:39 am ]
Post subject:  Re: ambient temperature sensor?
According to the FSM, the Ambient Air Temperature signal is used for various vehicle and engine functions:

    1. the PCM will also prevent the A/C compressor clutch from engaging when ambient temperatures are below about 1.0° C (50° F)
    2. Glow Plug operation-When the ignition (key) switch is placed in the ON position, a signal is sent from the sensors to the ECM relaying current engine coolant temperature and ambient air temperature. After receiving this signal, the ECM will determine if, when and for how long of a period the glow plugs should be activated. The PCM continually monitors the ambient air temperature and the glow plug pre-heater circuits to determine how long the glow plugs should be energized in their pre-heat operating mode.
    3. indirect inputs to the TCM: ² Ambient Temperature, the TCM determines the appropriate shift schedule and shift points, depending on the present operating conditions and driver demand.
    4. Ambient air temperature is monitored by the Electronic Vehicle Information Center Computer (EVIC) through ambient temperature sensor messages received from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus network. The PCM receives a hard wired input from the ambient temperature sensor.

:SOMBRERO:
Author:  flash7210 [ Sun Jun 11, 2017 8:21 am ]
Post subject:  Re: ambient temperature sensor?
Thank you.
Good information.

Interesting that the AC compressor is not supposed to turn on when below 50F.
Author:  TKB4 [ Sun Jun 11, 2017 1:29 pm ]
Post subject:  Re: ambient temperature sensor?
I guess if you use defrost mode that would override the data from ambient temp sensor if below 50 F?
Author:  flash7210 [ Mon Jul 03, 2017 12:56 pm ]
Post subject:  Re: ambient temperature sensor?
I decided to play around with ambient temp sensor.

Outside temp 90F, sensor resistance = 7200 ohms.
Then I put the sensor in fridge for about 10 min.
Inside fridge temp 40F, sensor resistance = 12000 ohms.

So I kept the sensor removed from the grille and in its place stuck a 10000 ohm resistor.
I estimate that the ECM now thinks its about 60F outside.
Then I took it for a test drive.
Didnt really notice any change in engine performance but I did notice a slight change transmission shifting behavior.
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