DTC B2979 (L and AUTO)

DTC B2979 or DTC indicator L and AUTO  : An Open in the A/C Pressure Sensor Circuit

DTCs (AC)

1. Problem verification

   - 1. Clear the DTC with the HDS.

   - 2. Turn the vehicle to the OFF (LOCK) mode then the ON mode.

   - 3. Do the Self-Diagnostic Function with the HDS or the climate control unit.

   - 4. Check for DTCs.

   DTC Description	DTC
   B2979 An open in the A/C pressure sensor circuit

   Is DTC B2979 or L and AUTO indicated?

   YES 

   Go to step 2.

   NO 

   Intermittent failure. Check for loose wires or poor connections on the A/C pressure sensor circuit.

2. Open wire check (SENSOR 5V line)

   - 1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Disconnect the following connectors.

   Climate control unit connector A (32P)

   A/C pressure sensor 3P connector

   - 3. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	A/C pressure sensor 3P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 5 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)
   Test point 2	A/C pressure sensor 3P connector No. 3

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The SENSOR 5V wire is not open. Go to step 3.

   NO 

   Repair an open in the wire between the climate control unit and the A/C pressure sensor.

3. Open wire check (SENSOR(COM) line)

   - 1. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	A/C pressure sensor 3P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 18 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)
   Test point 2	A/C pressure sensor 3P connector No. 1

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The SENSOR(COM) wire is not open. Go to step 4.

   NO 

   Repair an open in the wire between the climate control unit and the A/C pressure sensor.

4. Open wire check (PD SENSOR line)

   - 1. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode
   	Climate control unit connector A (32P): disconnected
   	A/C pressure sensor 3P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 20 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)
   Test point 2	A/C pressure sensor 3P connector No. 2

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The PD SENSOR wire is not open. Go to step 5.

   NO 

   Repair an open in the wire between the climate control unit and the A/C pressure sensor.

5. Climate control unit check 1

   - 1. Reconnect the climate control unit connector A (32P).

   - 2. Turn the vehicle to the ON mode.

   - 3. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle ON mode
   	A/C pressure sensor 3P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 5 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)
   Test point 2	Climate control unit connector A (32P) No. 18 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)

   Is there about 5 V?

   YES 

   Go to step 6.

   NO 

   Replace the climate control unit .

6. Climate control unit check 2

   - 1. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle ON mode
   	A/C pressure sensor 3P connector: disconnected
   Test point 1	Climate control unit connector A (32P) No. 18 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)

   Test point 2

   Climate control unit connector A (32P) No. 20 - Refer to: Climate Control Unit Connector For Inputs and Outputs (2019 2020 2021), or Climate Control Unit Connector For Inputs and Outputs (2016 2017 2018)

   Is there about 5 V?

   YES 

   Replace the A/C pressure sensor - Refer to: A/C Pressure Sensor Removal and Installation (Variable Capacity Compressor) or A/C Pressure Sensor Removal and Installation (Fixed Capacity Compressor) .

   NO 

   Replace the climate control unit .