Multiplex Communication System: Other Lexus IS I

Communication Outline

Communication is implemented among the combination meter, A/C ECU control assembly, body ECU, engine control module and anti-theft ECU, and among the body ECU and power window master SW.

Upon receiving signals from applicable switches such as the door lock control switch or door courtesy light switch, each ECU determines the conditions of the switches as well as of the doors. After converting this information into digital signals, each ECU outputs them to other ECUs via serial data communication. The ECU that receives these digital signals determines the conditions of the switches and doors so that it can implement various controls such as to activate a door lock motor.

However, if there are no changes in the input signals because no doors were opened and no switches were used within 30 seconds, the body ECU interrupts the communication to save electricity. Following this interruption, any changes in the input signals will cause the communication to resume.

PRE-CHECK

1. Diagnostic System Each ECU of this vehicle is connected by the communication bus and it transmits each signal by communication. This communication bus is self-diagnosed by the body ECU and it memorizes the DTC when it detects communication stop to the ECU or communication bus +B short or GND short. There is a possibility that the body ECU cannot self-diagnose accurately unless it doesn't work normal. Trouble shooting of the body electrical system should be done after confirming if the body ECU and open door indicator light works normal by the Basic Inspection (Check Body ECU Operation). See step 2. If the DTC of the ECU communication stop is output, there is a possibility of the connector disconnection or 2 communication buses open. (Scheme 20) It will not become abnormal with only 1 communication bus open. If 2 communication buses are open at the position, DTC of the ECU communication stop between those 2 buses is output. (Scheme 21)
2. Basic Inspection (Check Body ECU Operation) - 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 & TRUNK LID»(ref-154728) article. If the results are OK, replace the faulty body ECU located behind the left kick panel. If the results are not good, repair or replace the malfunction part.
3. Open Door Indicator Light Inspection - Check if the open door indicator light (located on the combination meter) 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, go to «USING INDICATOR LIGHT»(ref-154087-S25629859522003050200000) under RETRIEVING DIAGNOSTIC TROUBLE CODES. If the results are not good, repair the open door indicator light. See «INSTRUMENT PANEL»(ref-154166) article.

Scheme 20

Scheme 21

Using Hand-Held Tester

Note. DTCs are 4 digit numbers.

1. Prepare the hand-held tester and connect it to DLC3 located under the lower finish panel of the instrument panel. (Scheme 22)
2. Turn the ignition switch ON and switch the hand-held tester main switch ON.
3. Use the hand-held tester to check the DTCs then write them down. For operating instructions, see the hand-held tester instruction book.
4. Confirm the details of the DTCs. See «DIAGNOSTIC TROUBLE CODE INDEX»(ref-154087-S36802132942003050200000).

Scheme 22

Using Open Door Indicator Light

Note. DTCs are 2 digit numbers.

1. Using Diagnosis Check Wire (SST 09843-18020), connect terminals 11 (Tc) and 3 (E1) of the DLC1 located in the combination meter ECU. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000).
2. Turn the ignition switch ON.
3. Read and record the DTC on the open door indicator light. (Scheme 23)for DTC output examples.
4. Check for the problem using the DTC table. See «DIAGNOSTIC TROUBLE CODE INDEX»(ref-154087-S36802132942003050200000).
5. After completing the check, turn the ignition switch off and disconnect terminals Tc and E1.

Scheme 23