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.

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HOMESERVICE MANUALSTOYOTA2012PRIUS THREEREPAIR AND DIAGNOSIS (SINGLE PAGE)HEATING, VENTILATION & A/C (HVAC)HVAC CONTROL SYSTEMSAIR CONDITIONING SYSTEM (EXCEPT PLUG-IN) (DIAGNOSTIC CODES & CIRCUIT TESTS)AIR CONDITIONING SYSTEMCIRCUIT TESTSBACK-UP POWER SOURCE CIRCUITPROCEDURE

2012 Toyota Prius Three

Back-up Power Source Circuit: Procedure

2012 Toyota Prius ThreeSECTION Procedure

CHECK HARNESS AND CONNECTOR (A/C AMPLIFIER - BATTERY)

Disconnect the A/C amplifier connector.

Fig 1: Identifying A/C Amplifier Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Measure the voltage according to the value(s) in the table below.

Standard Voltage

Tester Connection	Condition	Specified Condition
L17-21 (B) - Body ground	Power switch off	11 to 14 V

TEXT IN ILLUSTRATION

*1	Front view of wire harness connector (to A/C Amplifier)

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK HARNESS AND CONNECTOR (A/C AMPLIFIER - BODY GROUND)

Disconnect the A/C amplifier connector.

Fig 2: Identifying A/C Amplifier Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Measure the resistance according to the value(s) in the table below.

Standard Resistance

Tester Connection	Condition	Specified Condition
L17-14 (GND) - Body ground	Always	Below 1 Ω

TEXT IN ILLUSTRATION

*1	Front view of wire harness connector (to A/C Amplifier)

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK → See step 3

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE. Refer to PROBLEM SYMPTOMS TABLE

RENDER: 1.0x

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.