DTC B0126, B0131, B0159, B0164, B0174, or B0179. Buick LeSabre 2003

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2003 🢒 LeSabre 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B0126, B0131, B0159, B0164, B0174, or B0179

Circuit Description

The following DTCs are for the temperature sensors monitored by the instrument panel module (IPM):

•	B0126 -- Upper right air temperature sensor

•	B0131 -- Lower right air temperature sensor

•	B0159 -- Ambient air temperature sensor

•	B0164 -- Inside air temperature sensor

•	B0174 -- Upper left air temperature sensor

•	B0179 -- Lower left air temperature sensor

The IPM monitors the temperature sensors to maintain the comfort level inside of the vehicle. The temperature sensors are a 2 wire negative temperature co-efficient thermistor. The IPM applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The IPM provides the ground to the air temperature sensors through the low reference circuit. The IPM monitors the voltage drop across the air temperature sensors and uses the inputs for automatic control calculations. When the air temperatures are cold, the resistance of the sensors are high and the voltage signals are high. When the air temperatures are hot, the resistance of the sensors are low and the voltage signals are low. The IPM converts the voltage values to count values where 1 V is approximately equal to 51 counts.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The IPM detects the sensor signal circuit is less than 0.09 volt (5 counts) or more than 4.90 volts (250 counts).

Conditions Taken When the DTC Sets

•	Ambient air temperature sensor

-	A default value of 2.50 volts (128 counts) will be substituted for the ambient air temperature sensor data by the IPM. The Outside Air Temp displayed on the scan tool is the default value. The Outside Air Temp displayed on the scan tool in the Open/Short Data list will be the actual value.

-	The HVAC control module will display - - for ambient air temperature when OFF.

-	The HVAC control module will display the set temperature when ON.

•	Inside air temperature sensor

A default value of 2.5 volts (128 counts) will be substituted for the inside air temperature sensor data by the IPM. The Inside Air Temp displayed on the scan tool will be the default value. The Inside Air Temp display on the scan tool in the Open/Short Data list will be the actual value.

•	HVAC duct temperature sensor

When the ambient air temperature is at or below 15°C (59°F), a default value of 4.80 volts (245 counts) will be substituted for the HVAC duct temperature sensor data by the IPM. The Duct Temp displayed on the scan will be the default value. The Duct Temp displayed on the scan tool in the Open/Short Data list will be the actual value.

When the ambient air temperature is at or above 16°C (60°F), a default value of 0.19 volt (10 counts) will be substituted for the HVAC duct temperature sensor data by the IPM. The Duct Temp displayed on the scan tool will be the default value. The Duct Temp displayed on the scan tool in the Open/Short Data list will be the actual value.

Conditions for Clearing the DTC

•	The DTC will become history if the IPM no longer detects a failure.

•	The history DTC will clear after 50 fault-free ignition cycles.

•	The DTC can be cleared by using a scan tool.

Diagnostic Aids

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

The operating range of the sensor is between 0.09-4.90 volts. If the scan tool displays a value between 0-0.08 volts or 4.91-5.0 volts, then the sensor is performing outside of its designed limits.

Tests for the proper operation of the circuit in the high voltage range.

Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

Tests the signal circuit for a short to ground.

Tests the signal circuit for a short to voltage, a high resistance, or an open.

Tests the reference circuit for a high resistance or an open.

Step

Action

Values

Yes

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

Did you perform the HVAC Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the appropriate temperature sensor parameter in the Instrument Panel Module Open/Short data list.

Does the scan tool indicate that the temperature sensor parameter is within the specified range?

0.09-4.90 V

Go to Diagnostic Aids

Go to Step 3

Turn OFF the ignition.
Disconnect the air temperature sensor.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the appropriate temperature sensor parameter.

Does the scan tool indicate that the temperature sensor parameter is more than the specified value?

4.90 V

Go to Step 4

Go to Step 5

Turn OFF the ignition.
Connect a 3-amp fused jumper wire between the air temperature sensor signal circuit and the low reference circuit of the temperature sensor.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the appropriate temperature sensor parameter.

Does the scan tool indicate that the temperature sensor parameter is less than the specified value?

0.09 V

Go to Step 8

Go to Step 6

Test the appropriate signal circuit of the temperature sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.