DTC B0174, B0179, B0510, or B0515. Cadillac XLR 2004

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B0174, B0179, B0510, or B0515

Circuit Description

The following DTCs are for the air temperature sensors located in the discharge air ducts:

•	DTC B0174 is for the upper left air temperature sensor.

•	DTC B0179 is for the lower left air temperature sensor.

•	DTC B0510 is for the upper right air temperature sensor.

•	DTC B0515 is for the lower right air temperature sensor.

Air temperature sensors allow the HVAC control module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 volt is approximately equal to 51 counts.

Conditions for Running the DTC

•	Battery voltage is within 8.7-16.5 volts.

•	The ignition is ON.

Conditions for Setting the DTC

The HVAC control module detects the signal circuit is less than 5 counts (0.09 volts) or greater than 250 counts (4.90 volts).

Action Taken When the DTC Sets

The HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.

Conditions for Clearing the DTC

•	The DTC will become history if the HVAC control module no longer detects a fault.

•	The history DTC will clear after 100 fault free ignition cycles.

•	The DTC can be cleared with a scan tool.

Test Description

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

Verifies that the temperature displayed is not within the calibrated range.

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.

Step

Action

Value(s)

Yes

Schematic Reference: HVAC Schematics

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the appropriate Duct Temp. Sensor parameter in the HVAC Systems Automatic data list.

Does the scan tool indicate that the appropriate Duct Temp. Sensor is within the specified range?

5-250 counts (0.09-4.90 V)

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

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 Duct Temp. Sensor Data parameter.

Does the scan tool indicate that the appropriate Duct Temp. Sensor is greater than the specified value?

250 counts (4.90 V)

Go to Step 4

Go to Step 5

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

Does the scan tool indicate that the appropriate Duct Temp. Sensor data parameter is less than the specified value?

5 counts (0.09 V)

Go to Step 8

Go to Step 6

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