Pinpoint Test G: B1B71:11 and B1B71:15
Climate Control System
Pinpoint Test G: B1B71:11 and B1B71:15
Normal Operation
Under normal operation, the evaporator discharge air temperature sensor receives a ground from the HVAC module. The sensor varies its resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls, the resistance rises. The HVAC module measures this resistance to determine the temperature at the sensor.
The evaporator discharge air temperature sensor is used for A/C compressor cycling. An accurate evaporator temperature is critical to prevent evaporator icing. The temperature measurement is used by the HVAC module to turn off the A/C compressor before the evaporator temperatures are cold enough to freeze the condensation. This prevents ice blockage of airflow over the evaporator core.
- DTC B1B71:11 (Evaporator Discharge Air Temperature Sensor: Circuit Short to Ground)- The module senses lower than expected voltage on the sensor feedback circuit, indicating a short to ground.
- DTC B1B71:15 (Evaporator Discharge Air Temperature Sensor: Circuit Short to Battery or Open)- The module senses greater than expected voltage on the sensor feedback circuit, indicating a short to voltage or an open circuit or sensor.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Evaporator discharge air temperature sensor
- HVAC module
PINPOINT TEST G : B1B71:11 AND B1B71:15
G1 CHECK THE SENSOR RESISTANCE
- Ignition OFF.
- Disconnect: Evaporator Discharge Air Temperature Sensor C296.
- Measure the resistance between the evaporator discharge air temperature sensor C296 terminals and compare to the table below.
Ambient Temperature Resistance -40°C (-40°F) 832,519-1,017,523 ohms -20°C (-4°F) 263,111-290,807 ohms 0°C (32°F) 91,058-100,644 ohms 20°C (68°F) 35,473-39,207 ohms 25°C (77°F) 28,500-31,500 ohms 40°C (104°F) 15,307-16,919 ohms 60°C (140°F) 7,171-7,925 ohms 100°C (212°F) 1,976-2,184 ohms 120°C (248°F) 1,131-1,251 ohms
Is the resistance within the specified values for the temperatures?
Yes
GO to G2.
No
INSTALL a new evaporator discharge air temperature sensor. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
G2 CHECK THE HVAC MODULE OUTPUT VOLTAGE
- Ignition ON.
- Press the AUTO button.
- Measure the voltage between evaporator discharge air temperature sensor C296-1, circuit VH406 (VT/BN), harness side and C296-2, circuit RH107 (GN/BU), harness side.
Is the voltage between 4.7 and 5.1 volts?
Yes
INSTALL a new evaporator discharge air temperature sensor. CLEAR the DTCs. REPEAT the self-test. If code returns, GO to G8.
No
If diagnosing DTC B1B71:15, GO to G3.
If diagnosing DTC B1B71:11, GO to G6.
G3 CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: HVAC Module C228A/C2356A.
- Ignition ON.
- Measure the voltage between ground and HVAC module C228A/C2356A-6, circuit VH406 (VT/BN), harness side and ground.
Is any voltage present?
Yes
REPAIR circuit VH406 (VT/BN) for a short to voltage. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
No
GO to G4.
G4 CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR AN OPEN
- Ignition OFF.
- Measure the resistance between HVAC module C228A/C2356A-6, circuit VH406 (VT/BN), harness side and evaporator discharge air temperature sensor C296-1, circuit VH406 (VT/BN), harness side.
Is the resistance less than 5 ohms?
Yes
GO to G5.
No
REPAIR circuit VH406 (VT/BN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
G5 CHECK THE SIGNAL RETURN CIRCUIT FOR AN OPEN
- Measure the resistance between HVAC module C228A/C2356A-10, circuit RH107 (GN/BU), harness side and evaporator discharge air temperature sensor C296-2, circuit RH107 (GN/BU), harness side.
Is the resistance less than 5 ohms?
Yes
GO to G8.
No
REPAIR circuit RH107 (GN/BU) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
G6 CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR A SHORT TO THE SIGNAL RETURN CIRCUIT
- Ignition OFF.
- Disconnect: HVAC Module C228A/C2356A.
- Measure the resistance between evaporator discharge temperature sensor C296-1, circuit VH406 (VT/BN), harness side and C296-2, circuit RH107 (GN/BU), harness side.
Is the resistance greater than 10,000 ohms?
Yes
GO to G7.
No
REPAIR circuit VH406 (VT/BN) for a short to circuit RH107 (GN/BU). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
G7 CHECK THE EVAPORATOR TEMPERATURE SENSOR FEEDBACK CIRCUIT FOR A SHORT TO GROUND
- Measure the resistance between HVAC module C228A/C2356A-6, circuit VH406 (VT/BN), harness side and ground.
Is the resistance greater than 10,000 ohms?
Yes
GO to G8.
No
REPAIR circuit VH406 (VT/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
G8 CHECK THE HVAC MODULE CONNECTION
- Inspect the module connectors for:
- corrosion.
- pushed-out terminals.
- damaged terminals.
- Connect and correctly seat all the HVAC module connectors.
- Clear the DTCs.
- Operate the system and verify the concern is still present.
Is the concern still present?
Yes
INSTALL a new HVAC module. TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.