GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 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: 394206 Size: MF
HVAC Components
Cell 68: ECC Module and Temperature Sensors
Handling ESD Sensitive Parts Notice
Cell 68: ECC Module and Temperature Sensors

Circuit Description

The lower discharge air temperature sensor is a thermistor used in order to control the signal voltage in the electronic climate control (ECC) module. The ECC 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 ECC module will receive a high voltage input. If the lower duct air temperature is hot, the thermistor resistance is low. Therefore, the ECC module will receive a low signal voltage input. The lower discharge air temperature sensor is used in order to enhance the temperature control. Refer to Sensor Resistance Table .

Conditions for Setting the DTC

When the ignition is ON, the ECC module will detect DTC B0181 any time that CKT 405 is near 5 volts or higher.

Action Taken When the DTC Sets

The ECC 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 may only be cleared by removing and restoring B+ or by using the scan tool.

Diagnostic Aids
    • The ECC 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 ECC 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 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 lower discharge 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 ECC module.

    4.

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

    5.

  5. This step replaces a defective lower discharge 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 ECC module.

    8.

  8. This step replaces a defective ECC 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 ECC module.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check

2

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the lower discharge air temperature sensor.
  3. Measure the resistance between the lower discharge 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 lower discharge air temperature sensor harness connector and ground.

Is the voltage within the specified range?

9-16 V

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 lower discharge air temperature sensor harness connector and ground.

Is continuity present?

--

Go to Step 10

Go to Step 8

7

Replace the lower discharge air temperature sensor. Refer to Floor Air Outlet Replacement .

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 lower discharge air temperature sensor.
  3. Reconnect the ECC module.
  4. Turn the ignition switch to the ON position.
  5. Clear any ECC module DTCs.

Does the DTC reset?

--

Go to Step 11

Go to Intermittents and Poor Connections Diagnosis in Wiring Systems

11

Replace the ECC module. Refer to Control Assembly Replacement .

Is the replacement complete?

--

Go to Diagnostic System Check

--

12

Measure the voltage on terminal A of the lower discharge 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

--