Volvo 850 ecc outside temp sensor shorted to ground

[JimBee]

After cleaning out the over front door temp sensors my only code is 1-2-1 outside temp sensor shorted to ground. I've read through the ecc manual and it notes that dtc but doesn't provide guidance on how to solve it or where in that circuit the short might be.

Of course, the relevant question is does that sensor being shorted to ground interfere with the proper functioning of the ecc control unit or circuits from the control unit to the fan?

I can see that it might if climate control is set to automatic though I've never used it that way. I usually just leave the dials at one setting and adjust fan speed (to minimize wear on the servor motors). Insights appreciated!

The schematics in the manual are scaled too small to read, unfortunately. They might hold the answer.

[jreed]

I found this diagnostic procedure... maybe you've already gone through this?

"DTC 1-2-1 OUTSIDE TEMP. SENSOR CIRCUIT SHORTED TO GROUND
1) Turn ignition off. Install Test Unit (981 3190) and
Adapter (981 3194) between ECC control module and harness connector.
See Fig. 3. Using ohmmeter, connect test leads between ground and test
unit pins No. 6, 9, 10 and 56. Ohmmeter should read zero ohms in each
terminal. If resistance is as specified, go to next step. If
resistance is not as specified, check for open circuit.
2) Disconnect Adapter (981 3194) from ECC control module. Disconnect outside temperature sensor (located on right rear of engine compartment). See Figs. 4 and 5. Connect ohmmeter leads between test unit pins No. 10 and 14. Ohmmeter should read infinity. If reading is as specified, go to next step. If reading is not as specified, check for shorted circuit between sensor harness connector and ECC control module.
3) Connect ohmmeter leads between outside temperature sensor
terminals. Resistance should be 8000-12,000 ohms. If resistance is not
as specified, replace outside temperature sensor. Clear and recheck
for codes.

[JimBee]

Okay, #3 looks like a possibility. But, really, If I thought it doesn't affect ecc operation when not used in automatic mode, I'd just let it be. Being right up front and close to the road after all these years and north of 200k miles I'd be surprised if it's not fouled by now. But would that throw the code? It could be a wire with crisped out insulation. I'll have to get in there to look closer.

[misha]

On these cars...in fact in almost every car ...if ambient temperature sensor is not working...ac will not start because ecc will not know what is ambient temperature in order to protect compressor...since ac will not work if ambient temperature is below 2C(when orange light for snow flake lights up).

It doesn't have anything with ecc in auto or manual mode.

For maintaining desired cabin temperature there are 2 sensors on driver's & passenger's side under grab handles on the roof.

Those sensors are used by ecc to reach and maintain cabin temperature.

When you put slider switch for blower fan in AUT ecc just controls blower fan speed via power stage.

Even if you slide it out of AUT it will still maintain set cabin temperature.
When you put distribution on AUT ecc just controls where the air will be distributed.

Solar sensor by the windshield on the center of the dash also play a role for ecc.

[JimBee]

Misha, thanks for those details. A/C on this car doesn't work, anyway, so no problem with that, so I won't need to worry about the outside temp sensor.

For heater use, I just usually leave the dials on one setting and adjust the fan speed.

You left me with a question about the solar sensor: What exactly is its role?

[misha]

Read this:

AC-HeaterSystem-Auto (2).pdf

(646.29 KiB) Downloaded 123 times

[JimBee]

The ecc tech manual is really helpful—I haven't seen that one before!
Thanks for the post.