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.

SYS.OK|MANUAL.DB● LIVE

HOMESERVICE MANUALSTOYOTA2012PRIUS THREEREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETUNE-UPSMART KEY SYSTEM (KEYLESS START) (EXCEPT PLUG-IN) (DIAGNOSTIC CODES & SYMPTOM TESTS)SMART KEY SYSTEM (FOR START FUNCTION)DTC B2274: ACC MONITOR MALFUNCTIONPROCEDURE

2012 Toyota Prius Three

DTC B2274: ACC Monitor Malfunction: Procedure

2012 Toyota Prius ThreeSECTION Procedure

CHECK HARNESS AND CONNECTOR (AUXILIARY BATTERY - POWER MANAGEMENT CONTROL ECU) See step 1
NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (AUXILIARY BATTERY - POWER MANAGEMENT CONTROL ECU)

OK: Go to next step
CHECK HARNESS AND CONNECTOR (POWER MANAGEMENT CONTROL ECU - BODY GROUND) See step 2
NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (POWER MANAGEMENT CONTROL ECU - BODY GROUND)

OK: Go to next step

INSPECT INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

Remove the instrument panel junction block assembly.

Fig 1: Inspecting Instrument Panel Junction Block Assembly
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
2A-43 - 2B-4	20°C (68°F)	101.25 to 123.75 Ω
2A-43 - 2B-6	20°C (68°F)	101.25 to 123.75 Ω
2B-4 - 2B-6	Always	Below 1 Ω

TEXT IN ILLUSTRATION

*1	Component without harness connected (Instrument Panel Junction Block Assembly)

NG → See step 7

OK: Go to next step

CHECK HARNESS AND CONNECTOR (POWER MANAGEMENT CONTROL ECU - INSTRUMENT PANEL J/B)

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

Standard Resistance

Tester Connection	Condition	Specified Condition
L6-1 (ACCD) - 2A-43	Always	Below 1 Ω
L6-1 (ACCD) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK HARNESS AND CONNECTOR (INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY - BODY GROUND)

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

Standard Resistance

Tester Connection	Condition	Specified Condition
2B-4 - Body ground	Always	Below 1 Ω
2B-6 - Body ground	Always	Below 1 Ω

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY - BODY GROUND)

OK: Go to next step

INSPECT POWER MANAGEMENT CONTROL ECU

Reinstall the instrument panel junction block assembly.

Fig 2: Inspecting Power Management Control ECU
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Reconnect the L5 and L6 connectors.

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

Standard Voltage

Tester Connection	Condition	Specified Condition
L6-1 (ACCD) - Body ground	Power switch on (ACC)	Output voltage at terminal AM21 or AM22 is -2.5 V or more

TEXT IN ILLUSTRATION

*1	Component with harness connected (Power Management Control ECU)

NG → See step 8

OK → See step 9

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY. Refer to REMOVAL
REPLACE POWER MANAGEMENT CONTROL ECU. Refer to REMOVAL
USE SIMULATION METHOD TO CHECK. Refer to HOW TO PROCEED WITH TROUBLESHOOTING

RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready Tools Free Quote Check Quote Shield Pro

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.