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Now this one is a little technical, and you might want to leave this one for your mechanic to look at. But unfortunately there is no way to make this one sound simple! So if you suspect that you have a faulty ambient sensor, print this out and take it to your mechanic, or really knowledgeable buddy, and get after it!! |
Note: On vehicles with an exterior mounted ambient temperature sensor the following operational parameters must be kept in mind when troubleshooting the system.
- Under most conditions the ambient temperature display does NOT update until the vehicle is driven over 15 MPH (25 KPH). This is NORMAL AND DOES NOT INDICATE A FAULT WITH THE CONTROL UNIT.
- If the temperature reading is increasing, the ECU will limit the temperature change to a rate of 1 degree F (.5 C) per minute.
Diagnose an inaccurate temperature indication
To diagnose an inaccurate temperature indication, first drive the vehicle above 15 MPH for several minutes to determine if the temperature reading adjusts to current conditions.
If the reading is still incorrect, check the resistance of the temperature sensor and compare it to the resistance values listed in the following chart:
| Temperature | Resistance |
-20' C (-4' F)= |
94.5k |
-10' C (14' F)= |
54.3K |
0 C (32' F)= |
32.1K |
10' C (50' F)= |
19.7K |
20; C (68' F)= |
12.5 K |
30' C (86' F)= |
8.1K |
40' C (104' F)= |
5.4K |
If sensor resistance is as specified, disconnect connectors C245 and C250.
NOTE: In each of the following checks, if the resistance exceeds 2 ohms it is considered excessive.
Perform a resistance check of the sensor wires as follows
NOTE: In each of the following checks, the resistance reading must be INFINITE!
- Check resistance between C245, terminal 8 and C250, terminal 1.
- Check resistance between C245, terminal 7 and C250, terminal 2.
- Repair any leads where the resistance exceeds 2 ohms and repeat test.
Check the sensor wires for a short.
With C245 and C250 disconnected, check the sensor wires for a short.
- Check resistance between C245 terminal 8 and ground.
- Check resistance between C245 terminal 7 and ground.
- Check resistance between C245 terminal 7 and C245 terminal 8.
- Repair any leads that have continuity in the above specs and repeat resistance and continuity checks.
- Install connectors C245 and C250 when repairs are complete.
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