Lexus RX (RX 350L, RX450h) 2016-2024 Repair Manual: How To Proceed With Troubleshooting

NOTICE:

• Because the order of diagnosis is important to allow correct diagnosis, make sure to begin troubleshooting using How to Proceed with Troubleshooting when CAN communication system related DTCs are output.
• If the CAN communication system is malfunctioning, check the contact pressure of the terminals in connectors, as insufficient terminal contact pressure may be the cause.

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• Refer to Diagnosis System for CAN communication system DTCs.
• Refer to troubleshooting of each system if DTCs regarding the CAN communication system are not output.
• Before measuring the resistance of the CAN bus, turn the engine switch off and leave the vehicle for 1 minute or more without operating the key or any switches, or opening or closing the doors. After that, disconnect the cable from the negative (-) battery terminal and leave the vehicle for 1 minute or more before measuring the resistance.
• After turning the engine switch off, waiting time may be required before disconnecting the cable from the negative (-) battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) battery terminal notices before proceeding with work.

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HINT:

• If the engine switch can be turned on (IG) (the power source mode can be changed to on (IG)) when the vehicle is brought in for repair, check for DTCs and check the illumination condition of the indicators in the combination meter assembly and the basic operation of the vehicle (such as steering operation) promptly.
• Do not turn the engine switch off until the inspection of the vehicle is finished, as some fail-safe functions are canceled when the engine switch is turned off.
• If the engine switch cannot be turned on (IG) (the power source mode cannot be changed to on (IG)) when the vehicle is brought in, measure the voltage of the battery. If the voltage is below 11 V, recharge or replace the battery before performing troubleshooting.
• If the engine switch cannot be turned on (IG) even though the battery voltage is normal, repair this malfunction before performing troubleshooting.

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HINT:

• When troubleshooting, confirm that the problem symptoms have been accurately identified. Preconceptions should be discarded in order to make an accurate judgment. To clearly understand what the problem symptoms are, it is extremely important to ask the customer about the problem and the conditions at the time the malfunction occurred.
• Ask the customer if the vehicle is/was equipped with additional devices such as a theft deterrent device or monitor. (If equipped, explain to the customer that the additional devices will be removed before performing troubleshooting as the malfunction cannot be checked properly.)

HINT:

• What was affected (system, part or meter warning indicators)
• What happened (details of the malfunction)
• When (occurrence date and time, frequency and if it recurs or not)
• Under what kind of situation did the problem occur (driving and operating condition at the occurrence and weather)
• Road type or condition (city, suburb, paved road, unpaved road, highway, etc.)
• Return conditions (what made the vehicle return to normal, for example, the engine switch was turned off)

HINT:

• If communication is not possible, the Techstream screen will indicate an error.
• If communication between the Techstream and ECUs is not possible, either the Techstream or vehicle has a malfunction.
• When communication between the Techstream and the vehicle is not possible, but communication is possible when the Techstream is connected to another vehicle, the vehicle is malfunctioning. Inspect the CANH and CANL branch lines of the DLC3 and the ECU power source circuits (in this case perform steps 31 to 32 first). In addition, check that the BAT terminal of the DLC3 receives battery voltage (11 V or more).
• If communication between the Techstream and ECUs is still not possible even when the Techstream is connected to another vehicle, the Techstream has a malfunction. Perform the self tests described in the Techstream operators manual. (The Techstream may be malfunctioning or its battery may be discharged.)

NOTICE:

• CAN communication DTCs are output when there is an open or short in any of the communication lines. Any problems with the power source of a corresponding ECU or sensor, or problems in the ECU or sensor itself also cause these DTCs to be output.
• If a CAN communication line connector is disconnected with the engine switch on (IG), the ECUs of the corresponding system and related systems store a DTC.

HINT:

• If an open in a CAN main bus line, a short between the CAN bus lines (CANH and CANL) or a short to ground or +B in a CAN bus occurs, DTCs of almost all ECUs and sensors on the CAN bus may be output (or a message indicating a communication error may be displayed on the Techstream screen). In this case, check the resistance of the CAN bus (steps 10 to 24) first.
• If an open occurs in just one of the lines of a CAN branch, DTCs which are not related to malfunctioning parts may be output (DTCs may be displayed randomly), or a message indicating a communication error may be displayed on the Techstream.

NOTICE:

• CAN communication DTCs are output when there is an open or short in any of the communication lines. Any problems with the power source of a corresponding ECU or sensor, or problems in the ECU or sensor itself also cause these DTCs to be output.
• If a CAN communication line connector is disconnected with the engine switch on (IG), the ECUs of the corresponding system and related systems store a DTC.

HINT:

• If an open in a CAN main bus line, a short between the CAN bus lines (CANH and CANL) or a short to ground or +B in a CAN bus occurs, DTCs of almost all ECUs and sensors on the CAN bus may be output (or a message indicating a communication error may be displayed on the Techstream screen). In this case, check the resistance of the CAN bus (steps 10 to 24) first.
• If an open occurs in just one of the lines of a CAN branch, DTCs which are not related to malfunctioning parts may be output (DTCs may be displayed randomly), or a message indicating a communication error may be displayed on the Techstream.

NOTICE:

• *: In this case, as the main body ECU (multiplex network body ECU) (Main Body) outputs communication DTCs (DTCs that start with U), the problem area can be determined from those DTCs.
• Non-installed ECUs or sensors will not be displayed. Do not mistake them for being in communication stop mode.
• It may be possible to select buses that do not have ECUs or sensors from the bus selection pull-down menu on the Techstream. This is not a malfunction. (This occurs when optional devices are not on a sub bus that is monitored by a gateway function equipped ECU.)

HINT:

• Regarding CAN Bus Check, refer to How to Interpret CAN Bus Check Screen.

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• If the detection status of ECUs changes during the inspection, one of the branch lines of a connected ECU or sensor may be open. (Signals from the ECU or sensor that has an open in one of its branch lines create electrical noise, affecting response to the Techstream and whether or not the ECUs and sensors are displayed.)
• Regarding the ECUs connected to sub bus 1, the main body ECU (multiplex network body ECU) displays communicating ECUs on the Techstream. If the communication between the main body ECU (multiplex network body ECU) and an ECU stops for 10 seconds or more, the ECU will no longer be displayed on the Techstream.
• Regarding the communication stop mode for ECUs connected to sub bus 1, refer to the inspection procedure for the DTCs that indicate a communication stop.

HINT:

• The term ''sub bus monitor ECU'' refers to a gateway function equipped ECU that is able to monitor a bus and store DTCs.
• When checking for communication DTCs, refer to How to Interpret Communication DTCs (DTCs that start with U).

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• Because a gateway function equipped ECU (sub bus monitor ECU) monitors signals from all ECUs that are connected to its sub bus, a gateway function equipped ECU can detect ECUs with a communication stop more accurately. In this case, perform troubleshooting by referring to the DTC combination table for the sub bus.

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• If communication DTCs are stored, and all ECUs and sensors connected to the CAN communication system are displayed on the CAN Bus Check screen of the Techstream, a past malfunction that is currently not occurring is suspected.
• When a CAN branch of the bus 1, bus 2, bus 3, bus 4 or bus 5 is malfunctioning, because the ECUs and sensors related to it detect the malfunction, the problem area can be determined using the combination of DTCs that are output.
• When sub bus 1 is malfunctioning, the main body ECU (multiplex network body ECU) detects a communication stop for connected ECUs and a network communication error, and stores DTCs.
• On the Techstream, the Main Body item displays the DTCs for ECUs connected to sub bus 1.
• When both the sub bus monitor ECU and the ECUs connected to the bus 1, bus 2, bus 3, bus 4 or bus 5 store communication DTCs, check and repair the corresponding sub bus first.

Problem Symptoms Table

Data List / Active Test

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