Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
The cost to diagnose the P0AA4 Lexus code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
The SMRs (System Main Relays) connect and disconnect the high-voltage power supply circuit in accordance with requests from the HV control ECU. To ensure a reliable operation, they consists of a total of 3 relays (1 for the negative side and 2 for the positive side).
To connect, SMR1 and SMR3 turn ON initially. Then, SMR2 turns ON and SMR1 turns OFF. This process protects the circuit from the high-voltage surge current by allowing the limit current to flow via the resistor. To disconnect, SMR2 and SMR3 turn OFF in that order. The HV control ECU checks that the relays have turned OFF properly.
The HV control ECU monitors the proper operation of the SMRs (CON1, CON2 and CON3) to check for a malfunction.
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