Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: PTC Heater Circuit

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Vehicle Interior / Heating / Air Conditioning / Air Conditioning System / PTC Heater Circuit

DESCRIPTION

The air conditioning amplifier assembly sends operation signals to the PTC heater relays when quick heater assembly operation conditions are met. Based on the signals from the air conditioning amplifier assembly, the PTC heater relays turn on, and power is supplied to the quick heater assembly installed in the air conditioning radiator assembly.

Quick Heater Assembly Operation Condition

Control ECU

Condition

Air Conditioning Amplifier Assembly

Engine running

Combination switch assembly (ECO mode switch) off

Blower switch: On

Temperature setting: MAX HOT

Light control switch off
  • Engine coolant temperature 65°C (149°F) or lower (3 PTC heater relays operating)
  • Engine coolant temperature 70°C (158°F) or lower (2 PTC heater relays operating)
  • Engine coolant temperature 75°C (167°F) or lower (1 PTC heater relay operating)
  • Ambient temperature -10°C (14°F) or lower (3 PTC heater relays operating)
  • Ambient temperature 0°C (32°F) or lower (2 PTC heater relays operating)
  • Ambient temperature 10°C (50°F) or lower (1 PTC heater relay operating)

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • If the battery voltage is low, the PTC heater may not operate. When "Operation of Electrical Items Restricted." is displayed on the multi-information display in the combination meter assembly, inspect the battery, referring to On-vehicle Inspection for the charging system.

    Click here

  • If the battery voltage is low, the PTC heater may not operate. When "Operation of Electrical Items Restricted." is not displayed on the multi-information display in the combination meter assembly, check the Data List item "Battery Control Count (Body ECU)".

    Click here

  • Inspect the fuses for circuits related to this system before performing the following procedure.

PROCEDURE

1.

PERFORM ACTIVE TEST USING TECHSTREAM

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

(d) Enter the following menus: Body Electrical / Air Conditioner / Active Test.

(e) Perform the Active Test according to the display on the Techstream.

Body Electrical > Air Conditioner > Active Test

Tester Display

Measurement Item

Control Range

Diagnostic Note

Heater Active Level

Quick heater assembly

Min.: 0, Max.: 3

-
Body Electrical > Air Conditioner > Active Test

Tester Display

Heater Active Level

OK:

Heater Active Level changes normally.

NG

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

OK

2.

INSPECT PTC HEATER RELAY

(a) Remove the PTC heater relays.

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

*a

Component without harness connected

(PTC HTR NO. 1)

*b

Component without harness connected

(PTC HTR NO. 2)

*c

Component without harness connected

(PTC HTR NO. 3)

-

-

Standard Resistance:

Tester Connection

Condition

Specified Condition

3 - 5

Battery voltage not applied between terminals 1 and 2

10 kΩ or higher

3 - 5

Battery voltage applied between terminals 1 and 2

Below 1 Ω
NG

REPLACE PTC HEATER RELAY

OK

3.

CHECK HARNESS AND CONNECTOR (PTC HEATER RELAY - POWER SOURCE)

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

Standard Voltage:

PTC HTR NO. 1

Tester Connection

Condition

Specified Condition

Relay terminal 5 - Body ground

Always

11 to 14 V

Relay terminal 1 - Body ground

Engine switch off

Below 1 V

Relay terminal 1 - Body ground

Engine switch on (IG)

11 to 14 V

Standard Voltage:

PTC HTR NO. 2

Tester Connection

Condition

Specified Condition

Relay terminal 5 - Body ground

Always

11 to 14 V

Relay terminal 1 - Body ground

Engine switch off

Below 1 V

Relay terminal 1 - Body ground

Engine switch on (IG)

11 to 14 V

Standard Voltage:

PTC HTR NO. 3

Tester Connection

Condition

Specified Condition

Relay terminal 5 - Body ground

Always

11 to 14 V

Relay terminal 1 - Body ground

Engine switch off

Below 1 V

Relay terminal 1 - Body ground

Engine switch on (IG)

11 to 14 V
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

CHECK HARNESS AND CONNECTOR (PTC HEATER RELAY - AIR CONDITIONING AMPLIFIER ASSEMBLY)

(a) Disconnect the J43 and J42 air conditioning amplifier assembly connectors.

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

Standard Resistance:

PTC HTR NO. 1

Tester Connection

Condition

Specified Condition

Relay terminal 2 - J43-18 (PTC1)

Always

Below 1 Ω

Relay terminal 2 or J43-18 (PTC1) - Body ground

Always

10 kΩ or higher

Standard Resistance:

PTC HTR NO. 2

Tester Connection

Condition

Specified Condition

Relay terminal 2 - J42-10 (PTC2)

Always

Below 1 Ω

Relay terminal 2 or J42-10 (PTC2) - Body ground

Always

10 kΩ or higher

Standard Resistance:

PTC HTR NO. 3

Tester Connection

Condition

Specified Condition

Relay terminal 2 - J42-11 (PTC3)

Always

Below 1 Ω

Relay terminal 2 or J42-11 (PTC3) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

5.

CHECK HARNESS AND CONNECTOR (PTC HEATER RELAY - QUICK HEATER ASSEMBLY AND BODY GROUND)

(a) Disconnect the J71 and J70 quick heater assembly connectors.

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

Standard Resistance:

PTC HTR NO. 1

Tester Connection

Condition

Specified Condition

Relay terminal 3 - J71-3 (B)

Always

Below 1 Ω

J71-2 (E) - Body ground

Always

Below 1 Ω

J70-1 (E) - Body ground

Always

Below 1 Ω

J71-3 (B) - Body ground

Always

10 kΩ or higher

Standard Resistance:

PTC HTR NO. 2

Tester Connection

Condition

Specified Condition

Relay terminal 3 - J70-2 (B)

Always

Below 1 Ω

J70-1 (E) - Body ground

Always

Below 1 Ω

J70-2 (B) - Body ground

Always

10 kΩ or higher

Standard Resistance:

PTC HTR NO. 3

Tester Connection

Condition

Specified Condition

Relay terminal 3 - J71-1 (B)

Always

Below 1 Ω

J71-2 (E) - Body ground

Always

Below 1 Ω

J71-1 (B) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

6.

INSPECT QUICK HEATER ASSEMBLY

(a) Remove the quick heater assembly.

Click here

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J71-1 (B) - J71-2 (E)

Always

Below 1 Ω

J71-3 (B) - J70-1 (E)

Always

Below 1 Ω

J71-3 (B) - J71-2 (E)

Always

Below 1 Ω

J70-2 (B) - J70-1 (E)

Always

Below 1 Ω

*a

Component without harness connected

(Quick Heater Assembly)
OK

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY

NG

REPLACE QUICK HEATER ASSEMBLY

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