GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Blazer - 4WD - RHD 🢒 DTC 🢒 DTC B0181 Output Air Temp Sensor 2 Circuit High

Object Number: 425170 Size: MF

Circuit Description

The lower duct air temperature sensor is a thermistor used to control the signal voltage in the electronic climate control module. The electronic climate control module supplies a reference voltage (about 5 volts) on CKT 405 (LT GRN) to the sensor. When the lower duct air temperature is cold, the thermistor resistance is high. Therefore, the electronic climate control module will receive a high voltage input. If the lower duct air temperature is hot, the thermistor resistance is low. Therefore, the electronic climate control module will receive a low signal voltage input. The duct air temperature sensor is used to enhance the temperature control. Refer to Sensor Resistance Table .

Conditions for Setting the DTC

When the ignition switch is in the ON position, the electronic climate control module will detect DTC B0181 any time CKT 405(LT GRN) is near 5 volts or higher.

Action Taken When the DTC Sets

The electronic climate control module will use a default value of 245 A/D counts until the fault goes away or is repaired.

Conditions for Clearing the MIL/DTC

This fault will clear as soon as the fault goes away or has been repaired. The system will then return to normal operation. History DTCs can only be cleared by removing and restoring B+ or by using the scan tool.

Diagnostic Aids
    • The electronic climate control module may set class 2 lost communication DTCs when the body control module (BCM) or the vehicle control module (VCM) is being reprogrammed. After reprogramming, inspect for DTCs in the electronic climate control module. Clear any history U DTCs, then resume diagnostics.
    • Visually inspect the sensor connector and harness for corrosion and damage. The resistance value of the sensor must be within 334-100,865 ohms. Refer to Sensor Resistance Table . If resistance is not within specifications, replace the sensor.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step measures the resistance of the output of the duct air temperature sensor.

    2.

  2. This step inspects for B+ on CKT 405.

    3.

  3. This step determines if the short to B+ is in CKT 405 or in the electronic climate control module.

    4.

  4. This step inspects for an open in CKT 552.

    5.

  5. This step replaces a defective duct air temperature sensor.

    6.

  6. This step repairs an open in CKT 552.

    7.

  7. This step inspects for intermittents and tests for a malfunctioning electronic climate control module.

    8.

  8. This step replaces a defective electronic climate control module.

    9.

  9. This step inspects for 5 volts on CKT 405.

    10.

  10. This step determines if the open is in CKT 405 or in the electronic climate control module.

Step

Action

Value(s)

Yes

No

Tools Required

    • Scan Tool
    • J 39200 Digital Multimeter (DMM)
    • J 35616-A Connector Test Adapter Kit

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the duct air temperature sensor.
  3. Measure the resistance between the duct air temperature sensor terminal A and terminal B.
  4. Compare the reading to the Temperature/Resistance table. Refer to Sensor Resistance Table .

Is the resistance within the range specified in the table?

--

Go to Step 3

Go to Step 7

3

  1. Turn the ignition switch to the ON position.
  2. Measure the voltage at terminal A of the duct air temperature sensor harness connector and ground.

Is battery voltage present?

--

Go to Step 4

Go to Step 12

4

Inspect for a short to B+ in CKT 405 (LT GRN).

Did you find a short to B+?

--

Go to Step 5

Go to Step 11

5

Repair the short to B+ in CKT 405 (LT GRN).

Is the repair complete?

--

Go to Diagnostic System Check

--

6

Inspect for continuity to ground at terminal B of the duct air temperature sensor harness connector and ground.

Is continuity present?

--

Go to Step 10

Go to Step 8

7

Replace the duct air temperature sensor.

Is the replacement complete?

--

Go to Diagnostic System Check

--

8

Inspect for an open in CKT 552 (BLK).

Did you find an open?

--

Go to Step 9

Go to Step 11

9

Repair the open in CKT 552 (BLK).

Is the repair complete?

--

Go to Diagnostic System Check

--

10

  1. Turn the ignition switch to the OFF position.
  2. Reconnect the duct air temperature sensor.
  3. Reconnect the electronic climate control module.
  4. Turn the ignition switch to the ON position.
  5. Clear any electronic climate control module DTCs.

Does the DTC reset?

--

Go to Step 11

Go to Intermittents and Poor Connections Diagnosis in Wiring Systems

11

Replace the electronic climate control module.

Is the replacement complete?

--

Go to Diagnostic System Check

--

12

Measure the voltage on terminal A of the duct air temperature sensor to ground.

Does the voltage equal the specified value?

5 V

Go to Step 6

Go to Step 13

13

Inspect for an open in CKT 405 (LT GRN).

Did you find an open?

--

Go to Step 14

Go to Step 11

14

Repair the open in CKT 405 (LT GRN).

Is the repair complete?

--

Go to Diagnostic System Check

--