DTC P0597-14: Thermostat Heater Control Circuit Short to Ground or Open [03/2023 - ]: Procedure

WARNING: This page is about a different car, the 2025 Lexus NX 250, 2024 Lexus NX 250, 2023 Lexus NX 250, and 2022 Lexus NX 250. However, it is still accessible from the selected car via links, so may be relevant.

CHECK TERMINAL VOLTAGE (POWER SOURCE OF WATER INLET WITH THERMOSTAT SUB-ASSEMBLY)

Disconnect the water inlet with thermostat sub-assembly connector.
Turn the ignition switch to ON.

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

Standard Voltage

Tester Connection	Condition	Specified Condition
V4-1 - Body ground	Ignition switch ON	11 to 14 V

Result

Proceed to
OK
NG

Result:

See step 4

Result:

See step 2

INSPECT WATER INLET WITH THERMOSTAT SUB-ASSEMBLY
Refer to INSPECTION [11/2021 - ]

Result

Proceed to

OK

NG

Result:

NG

REPLACE WATER INLET WITH THERMOSTAT SUB-ASSEMBLY. Refer to REMOVAL [11/2021 - ]

Result:

OK

See step 3

CHECK HARNESS AND CONNECTOR (WATER INLET WITH THERMOSTAT SUB-ASSEMBLY - ECM)

Disconnect the water inlet with thermostat sub-assembly connector.
Disconnect the ECM connector.

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

Standard Resistance (for TMMC Made)

Tester Connection	Condition	Specified Condition
V4-2 - B94-7 (HTHM)	Always	Below 1 Ω
V4-2 or B94-7 (HTHM) - Body ground and other terminals	Always	10 kΩ or higher

Standard Resistance (for TMC Made)

Tester Connection	Condition	Specified Condition
V4-2 - B50-7 (HTHM)	Always	Below 1 Ω
V4-2 or B50-7 (HTHM) - Body ground and other terminals	Always	10 kΩ or higher

Result

Proceed to
OK
NG

Result:

REPLACE ECM. Refer to REMOVAL [11/2021 - ]

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR

INSPECT EFI-MAIN NO. 2 RELAY
Refer to PROCEDURE - Step 4

Result

Proceed to

OK

NG

Result:

NG

REPLACE EFI-MAIN NO. 2 RELAY

Result:

OK

See step 5

CHECK TERMINAL VOLTAGE (POWER SOURCE OF EFI-MAIN NO. 2 RELAY)

Remove the EFI-MAIN NO. 2 relay from the No. 1 engine room relay block and No. 1 junction block assembly.

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*1	No. 1 Engine Room Relay Block and No. 1 Junction Block Assembly
*2	EFI-MAIN NO. 2 Relay

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

Standard Voltage

Tester Connection	Condition	Specified Condition
3 (EFI-MAIN NO. 2 relay) - Body ground	Always	11 to 14 V

Result

Proceed to
OK
NG

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR (BATTERY - EFI-MAIN NO. 2 RELAY)

Result:

See step 6

CHECK HARNESS AND CONNECTOR (EFI-MAIN NO. 2 RELAY - BODY GROUND)

Remove the EFI-MAIN NO. 2 relay from the No. 1 engine room relay block and No. 1 junction block assembly.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
1 (EFI-MAIN NO. 2 relay) - Body ground	Always	Below 1 Ω

Result

Proceed to
OK
NG

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR

Result:

See step 7

CHECK HARNESS AND CONNECTOR (EFI-MAIN NO. 2 RELAY - WATER INLET WITH THERMOSTAT SUB-ASSEMBLY)

Remove the EFI-MAIN NO. 2 relay from the No. 1 engine room relay block and No. 1 junction block assembly.
Disconnect the water inlet with thermostat sub-assembly connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
5 (EFI-MAIN NO. 2 relay) - V4-1	Always	Below 1 Ω
5 (EFI-MAIN NO. 2 relay) or V4-1 - Body ground and other terminals	Always	10 kΩ or higher

Result

Proceed to
OK
NG

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR (EFI-MAIN NO. 1 RELAY - EFI-MAIN NO. 2 RELAY)

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR