Symptom:
*INCORRECT TEMP READING BEYOND +/-5
POSSIBLE CAUSES
*AMBIENT TEMPERATURE SENSOR
*AMBIENT TEMPERATURE SENSOR GROUND CIRCUIT OPEN
*AMBIENT TEMPERATURE SENSOR SIGNAL SHORT TO GROUND
*AMBIENT TEMPERATURE SENSOR SIGNAL CIRCUIT OPEN
*C0MPASS/MINI-TRIP COMPUTER
TEST
ACTION
APPLICABILITY
1
NOTE: Ensure that the CMTC is communicating on the PCI Bus before
proceeding with this test.
NOTE: Diagnose any PCM or HVAC DTCs before proceeding with this test.
The Ambient Temperature Sensor is hard-wired to the HVAC control head.
Ambient temperature information is transmitted to the CMTC on the PCI
Bus.
Turn the ignition off.
Disconnect the Ambient Temperature Sensor harness connector.
NOTE: To ensure accurate diagnosis of the CMTC temperature display, refer
to the following statements.
Ensure the CMTC display is in the desired mode of either Celsius or Farenheit.
The temperature display is updated based on time and vehicle speed.
At higher speeds, the temperature display is updated more frequently than at lower
speeds.
To ensure accurate temp display, vehicle should be test driven at speeds which permit
sufficient air flow over the Ambient Temperature Sensor.
This will prevent the Sensor from experiencing a
9hot soak9 condition which can
result in temperature displays higher than the actual ambient temperature.
Measure the resistance of the Ambient Temperature Sensor using the following
values:
0°C (32°F) Sensor resistance = 29.33 - 35.99 Kilohms.
10°C (50°F) Sensor resistance = 17.99 - 21.81 Kilohms
20°C (68°F) Sensor resistance = 11.37 - 13.61 Kilohms
25°C (77°F) Sensor resistance = 9.12 - 10.88 Kilohms
30°C (86°F) Sensor resistance = 7.37 - 8.75 Kilohms
40°C (104°F) Sensor resistance = 4.90 - 5.75 Kilohms
50°C (122°F) Sensor resistance = 3.33 - 3.88 Kilohms
Does the resistance measure between the min/max specifications for the current
ambient temperature?
All
Yes
→
Go To
2
No
→
Replace the Ambient Temperature Sensor.
Perform BODY VERIFICATION TEST - VER 1.
165
COMPASS/MINI-TRIP COMPUTER