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Makes 🢒 GMC_Truck 🢒 1998 🢒 Sonoma Pickup - 2WD 🢒 DTC 🢒 DTC B0181 Output Air Temp Sensor 2 Circuit High

DTC B0181 Output Air Temp Sensor 2 Circuit High Lower


Object Number: 283803 Size: MF

Circuit Description

The output air temperature sensor #2 (lower) is a thermistor used to control the signal voltage in the heater and A/C control module. The heater and A/C control module supplies a reference voltage (about 5 volts) on CKT 405 to the sensor. When the lower duct air temperature is cold, the thermistor resistance is high. Therefore, the heater and A/C control module will receive a high voltage input. If the lower duct air temperature is hot, the thermistor resistance is low. Therefore, the heater and A/C control module will receive a low signal voltage input. The output air temperature sensor #2 (lower) is used to enhance the temperature control. Refer to Sensor Resistance Table .

Conditions for Setting the DTC

When the ignition is ON, the heater and A/C control module will detect DTC B0181 any time that CKT 405 is near 5 volts or higher.

Action Taken When the DTC Sets

The heater and A/C 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 heater and A/C control module may set class 2 lost communication DTCs when the BCM or the VCM is being reprogrammed. After reprogramming, inspect for DTCs in the heater and A/C 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 334-100,865 ohms. Refer to the Temperature vs 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 output air temperature sensor #2.

    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 heater and A/C control module.

    4.

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

    5.

  5. This step replaces a defective output air temperature sensor #2.

    6.

  6. This step repairs an open in CKT 552.

    7.

  7. This step inspects for intermittents and tests for a malfunctioning heater and A/C control module.

    8.

  8. This step replaces a defective heater and A/C 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 heater and A/C control module.

Step

Action

Value(s)

Yes

No

1

  1. Turn the ignition to the OFF position.
  2. Disconnect output air temperature sensor #2.
  3. Measure the resistance between passenger compartment sensor terminals A and B.
  4. Compare the reading to the Temperature/Resistance table. Refer to Sensor Resistance Table .

Is the resistance within the specified range?

--

Go to Step 2

Go to Step 5

2

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

Is the voltage within the specified range?

9-16 V

Go to Step 3

Go to Step 9

3

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

Is the repair complete?

--

Go to Diagnostic System Check

Go to Step 8

4

Inspect for continuity to ground at terminal B of the output air temperature sensor #2 harness connector and ground.

Is continuity indicated?

--

Go to Step 7

Go to Step 6

5

Replace output air temperature sensor #2.

Is the repair complete?

--

Go to Diagnostic System Check

--

6

Inspect CKT 552 (BLK) for an open.

Is the repair complete?

--

Go to Diagnostic System Check

Go to Step 8

7

  1. Turn the ignition to the OFF position.
  2. Reconnect the output air temperature sensor #2.
  3. Reconnect the heater and A/C control module.
  4. Turn the ignition to the ON position.
  5. Clear any heater and A/C control module DTCs.

Does the DTC reset?

--

Go to Step 8

Go to Wiring Systems

8

Replace the heater and A/C control module.

Is the repair complete?

--

Go to Diagnostic System Check

--

9

Use a J 39200 in order to ground and measure the voltage on terminal A of output air temperature sensor #2.

Does the voltage indicate the specified value?

5V

Go to Step 4

Go to Step 10

10

Inspect CKT 405 (LT GRN) for an open.

Is the repair complete?

--

Go to Diagnostic System Check

Go to Step 8