Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC B2979 or DTC Indicator B and WINDSHIELD DEFROST: An Open In the A/C Pressure Sensor Circuit
- Clear the DTC with the HDS.
- Turn the ignition switch to LOCK (0), and then ON (II).
- Do the self-diagnostic with the HDS (see HOW TO USE THE HDS TO CHECK FOR DTCS ) or climate control unit (see HOW TO USE THE CLIMATE CONTROL UNIT SELF-DIAGNOSTIC FUNCTION WITHOUT THE HDS ).
- Check for DTCs.
Is DTC B2979 or B and WINDSHIELD DEFROST indicated?
YES - Go to step 5.
NO - Intermittent failure, check for loose wires or poor connections on the A/C pressure sensor circuit. ■
- Turn the ignition switch to LOCK (0).
- Disconnect the A/C pressure sensor 3P connector.
- Disconnect climate control unit connector A (36P) and B (20P).
- Check for continuity between the following terminals of climate control unit connectors A (36P), B (20P) and the A/C pressure sensor 3P connector.
36P: 3P:
No. 22 No. 3
36P: 3P:
No. 4 No. 1
No. 6 No. 2
Is there continuity?
YES - Go to step 9.
NO - Repair open in the wire(s) between the climate control unit and the A/C pressure sensor. ■
- Reconnect climate control unit connectors A (36P) and B (20P).
- Turn the ignition switch to ON (II).
- Measure the voltage between climate control unit connector A (36P) terminal No. 22 and climate control unit connector B (20P) terminal No. 4 and No. 6 individually.
Is there about 5 V?
YES - Replace the A/C pressure sensor. ■
NO - Check for loose wires or poor connections at climate control unit connectors A (36P), B (20P) and at the A/C pressure sensor 3P connector. If the connections are good, substitute a known-good climate control unit, and recheck. If the symptom/indication goes away, replace the original climate control unit (see CLIMATE CONTROL UNIT REMOVAL/INSTALLATION ). ■
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.