WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.

Diagnosis System -
- Each ECU of this vehicle is connected by communication bus and it transmits each signal by communication. This communication bus is self-diagnosed by body ECU No. 1 and it memorizes DTC when it detects communication stop to ECU or communication bus +B short or GND short. There is a possibility that body ECU No. 1 cannot self-diagnose accurately if it doesn't work normal. So, please note that the trouble shooting of the body electrical system should be done after confirming the body ECU No. 1 and open door indicator works normally by the Basic Inspection.
- If the DTC of the ECU communication stop is output, there is a possibility of connector disconnection or 2 communication buses open. See Fig 1. It will not become abnormal with only 1 communication bus open.
- If 2 communication buses are open at the position as shown in the illustration, DTC of ECU communication stop between those 2 buses is output. See Fig 2.
Basic Inspection - Inspect the body ECU operation. With this inspection, the body ECU can be diagnosed if it works normal or not. Check if the luggage compartment door opener works normal. If the results are OK, go to step 3. If the results are not good, check the luggage compartment door opener system (except body ECU). See POWER DOOR LOCKS & LIFTGATE article under DOOR LOCKS & ANTI-THEFT SYSTEMS in ACCESSORIES & EQUIPMENT. If the results are OK, replace the body ECU. If the results are not good, repair or replace the malfunction part.
Open Door Indicator Light Inspection - Check if the open door indicator light is turned on when either door is open. If the open door indicator light is not turned on, DTC will not be output. If the results are OK, check the DTC. Go to USING INDICATOR LIGHT under RETRIEVING DIAGNOSTIC TROUBLE CODES. If the results are not good, repair the open door indicator light. See INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT.

Fig 1: Identifying ECU Communication Stop DTC Output

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Self-Diagnostic System: Pre-Check

Use the Manual With the Right Hardware

When to See a Mechanic

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