Toyota Avalon (XX50) 2019-2022 Service & Repair Manual: Thermostat Heater Control Circuit Short to Battery (P059712)

DESCRIPTION

An electric heater is equipped to the temperature sensing portion of the thermostat. During normal driving, current does not flow to the heater and the thermostat functions as an ordinary thermostat. When the temperature of the engine increases by a large amount such as during high-load driving, control is performed to warm the heater of the temperature sensing portion, forcing the valve to open and causing a large amount of coolant to flow from the radiator.

MONITOR DESCRIPTION

The ECM monitors the output voltage while the thermostat heater is operating.

The thermostat heater turns on and off according to ON/OFF switching of a transistor inside the ECM.

If a continuous mismatch occurs between the ECM transistor state and the output voltage, the ECM determines there is a malfunction in the thermostat heater circuit and stores a DTC.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

TYPICAL MALFUNCTION THRESHOLDS

CONFIRMATION DRIVING PATTERN

HINT:

• After repair has been completed, clear the DTC and then check that the vehicle has returned to normal by performing the following All Readiness check procedure.

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• When clearing the permanent DTCs, refer to the "CLEAR PERMANENT DTC" procedure.

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1. Connect the Techstream to the DLC3.
2. Turn the power switch on (IG).
3. Turn the Techstream on.
4. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
5. Turn the power switch off and wait for at least 30 seconds.
6. Turn the power switch on (IG).
7. Turn the Techstream on.
8. Put the engine in Inspection Mode (Maintenance Mode).

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9. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher [A].
10. Enter the following menus: Powertrain / Engine / Data List / Calculate Load and Coolant Temperature.
11. With the engine running, drive the vehicle for at least 3 seconds at the Calculate Load of 45% or more and the Coolant Temperature of 90°C (194°F) or higher [B].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

    HINT:

    If the engine stops, further depress the accelerator pedal to restart the engine.

12. Stop the vehicle.
13. Enter the following menus: Powertrain / Engine / Trouble Codes [C].
14. Read the pending DTCs.

    HINT:

    • If a pending DTC is output, the system is malfunctioning.
    • If a pending DTC is not output, perform the following procedure.
15. Enter the following menus: Powertrain / Engine / Utility / All Readiness.
16. Input the DTC: P059712.
17. Check the DTC judgment result.

    Techstream Display	Description
    NORMAL	DTC judgment completed System normal
    ABNORMAL	DTC judgment completed System abnormal
    INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions

    HINT:

    • If the judgment result is NORMAL, the system is normal.
    • If the judgment result is ABNORMAL, the system has a malfunction.
    • If the judgment result is INCOMPLETE, perform the steps [B] through [C] again.
    • [A] to [C]: Normal judgment procedure.

      The normal judgment procedure is used to complete DTC judgment and also used when clearing permanent DTCs.

    • When clearing the permanent DTCs, do not disconnect the cable from the auxiliary battery terminal or attempt to clear the DTCs during this procedure, as doing so will clear the universal trip and normal judgment histories.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

• Inspect the fuses for circuits related to this system before performing the following procedure.
• Vehicle Control History may be stored in the hybrid vehicle control ECU assembly if the engine is malfunctioning. Certain vehicle condition information is recorded when Vehicle Control History is stored. Reading the vehicle conditions recorded in both the Freeze Frame Data and Vehicle Control History can be useful for troubleshooting.

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  (Select Powertrain in Health Check and then check the time stamp data.)

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• If any "Engine Malfunction" Vehicle Control History item has been stored in the hybrid vehicle control ECU assembly, make sure to clear it. However, as all Vehicle Control History items are cleared simultaneously, if any Vehicle Control History items other than "Engine Malfunction" are stored, make sure to perform any troubleshooting for them before clearing Vehicle Control History.

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HINT:

Read Freeze Frame Data using the Techstream. The ECM records vehicle and driving condition information as Freeze Frame Data the moment a DTC is stored. When troubleshooting, Freeze Frame Data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

PROCEDURE

(a) Disconnect the thermostat heater (water inlet with thermostat sub-assembly) connector.

(b) Disconnect the ECM connector.

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

Standard Resistance:

OK

REPLACE ECM

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR