Multiplex Communication System: Diagnosis Lexus IS I

TROUBLE SHOOTING

1. Trouble shooting of a multiplex communication system complaint begins with verification of the customer problem. If problem occurs, go to step 3 . If problem does not occur, go to next step.
2. If problem does not occur, review conditions under which problem occurred for customer and try to duplicate those conditions. For example, if the problem occurs on rainy days or during high humidity conditions, sprinkle water onto vehicle and see if malfunction occurs. DO NOT sprinkle water directly into engine compartment or onto electronic components. Visually inspect for signs of mechanical and electrical damage. Inspect for blown fuses and damaged relays. Inspect for loose or corroded connections, damaged wiring harnesses and/or switches. Check for a broken or partially broken wire inside insulation, which could cause system malfunction but prove good in a continuity/voltage check with system disconnected. Ensure any aftermarket electronic equipment is properly installed. If fault is found, repair as necessary. If problem still cannot be created, go to next step.
3. Perform pre-check. See «PRE-CHECK»(ref-154087-S21971495052003050200000) under SELF-DIAGNOSTIC SYSTEM. If there is a normal code, go to the next step. If there is a malfunction code, go to step 5 .
4. Determine problem symptom. Engine. See «SELF-DIAGNOSTICS - IS300»(ref-134940) article under FAULT ISOLATION in ENGINE PERFORMANCE. Body Control System. See «BODY CONTROL SYSTEM»(ref-154127) article. Air Conditioning System. See «AUTOMATIC A/C-HEATER SYSTEMS - IS 300»(ref-174966) article in HVAC. Instrument Panel System. See «INSTRUMENT PANEL»(ref-154166) article. Anti-Theft System. See «ANTI-THEFT SYSTEM»(ref-154902) article.
5. Inspect multiplex communication circuits. See «DIAGNOSTIC TESTS»(ref-154087-S42553314942003050200000) .
6. After problem has been identified and repaired, confirm repairs. See «CONFIRMATION TEST»(ref-154087-S05228370742003050200000) under SELF-DIAGNOSTIC SYSTEM.

DIAGNOSTIC TROUBLE CODES

DIAGNOSTIC TROUBLE CODE INDEX

CLEARING DIAGNOSTIC TROUBLE CODES

The DTC will be cleared when the trouble output to DTC is recovered normally.

CONFIRMATION TEST

After repairs have been completed, confirm that problem has been eliminated. Operate system under same conditions recorded for original complaint. If problem is no longer present and no DTCs are present, repair has corrected problem. If problem is still present or DTCs are reset, further diagnosis and repair is required.

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Circuit Description

This DTC is output when communication stops between the power window master switch ECU and body ECU. (Scheme 9)

Detecting Condition - No communication from the power window master switch ECU more than 10 seconds.

Trouble Area

1. Power Window Master Switch ECU
2. Wiring Harness

Scheme 9

Diagnostic Procedure

1. Check if driver door window glass auto up function operates. With this inspection, the power window master ECU can be diagnosed if it works normally or not. If the results are OK, go to the next step. If the results are not good, replace the faulty power window master switch. See «POWER WINDOWS»(ref-154768) article under WINDOWS in ACCESSORIES & EQUIPMENT.
2. Disconnect the connector of the body ECU and P8 of the power window master switch. Check the continuity between terminal 6 (MPX3) of the body ECU and terminal 18 (TX) of the power window master switch. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000) . If there is continuity in the wiring harness, replace the faulty power window master switch. See «POWER WINDOWS»(ref-154768) article under WINDOWS in ACCESSORIES & EQUIPMENT. If there is an open in the wiring harness, repair it. If there is not continuity, repair or replace the faulty wiring harness. See «POWER WINDOWS»(ref-141321-S38370941532002121100000) in SYSTEM WIRING DIAGRAMS article.

For circuit diagram (Scheme 10)

Trouble Area

1. Wiring Harness
2. ECU

Scheme 10

1. Check the communication circuit inside the power window master switch ECU. Disconnect the P8 connector of the power window master switch. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000) . Check the DTC. If DTC B1214/14 or B1215/15 is not output, replace the faulty power window master switch. See «POWER WINDOWS»(ref-154768) article under WINDOWS in ACCESSORIES & EQUIPMENT. If DTC B1214/14 or B1215/15 is output, go to the next step.
2. Check for a short circuit between the power window master switch and body ECU. Connect the P8 connector of the power window master switch. Disconnect the connector of the body ECU from the driver side junction block. See «BODY ECU»(ref-154087-S17191193802003061900000) under REMOVAL & INSTALLATION. Check the DTC. If DTC B1214/14 or 1215/15 is not output, repair or replace the faulty wiring harness between the power window master switch and body ECU. See «POWER WINDOWS»(ref-141321-S38370941532002121100000) in SYSTEM WIRING DIAGRAMS article. If DTC B1214/14 or B1215/15 is output, replace the faulty body ECU located on the driver side junction block behind the left kick panel. See «BODY ECU»(ref-154087-S17191193802003061900000) under REMOVAL & INSTALLATION.

This DTC notifies how the switch works as follows: If the DTC is not output when operating the switch, it means failure of switch contact. If the DTC is output when not operating switch, it means switch is stuck. When something wrong is found by this diagnosis, inspect each switch. Then replace the faulty switch if there is a problem, or check the wiring harness if there is no problem.

Detecting Condition - Stuck switch.

Trouble Area - Power Window Master Switch.

Diagnosis Procedure

For switch inspection, refer to POWER WINDOWS article under WINDOWS in ACCESSORIES & EQUIPMENT. For power windows wiring diagram, see POWER WINDOWS in SYSTEM WIRING DIAGRAMS article.

For circuit diagram (Scheme 11)

Detecting Condition - Ground short of body ECU connector B5 terminal 2 (RDA).

Trouble Area

1. Wiring Harness.
2. Wireless Door Lock Tuner.
3. Body ECU.

Scheme 11

1. Disconnect the wireless door lock tuner and B5 body ECU connectors. Check the continuity between connector B5 terminal 2 (RDA) of the body ECU wiring harness and body ground. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000) . If there is no continuity, go to the next step. If there is continuity, repair or replace the faulty wiring harness. See «POWER DOOR LOCKS»(ref-141321-S40502153732002121100000) in SYSTEM WIRING DIAGRAMS article.
2. Connect the connector of the body ECU. Check the DTC. If DTC B1242/42 is not output, replace the faulty tuner. If DTC B1242/42 is output, replace the faulty body ECU located on the driver side junction block behind the left kick panel. See «BODY ECU»(ref-154087-S17191193802003061900000) under REMOVAL & INSTALLATION.

This DTC is output when failure of the light sensor is detected. (Scheme 12)

Detecting Condition

1. Malfunction of the light sensor.
2. Open or short of the light sensor circuit.

Trouble Area

1. Light Sensor.
2. Wiring Harness.
3. Anti-theft ECU.

Scheme 12

1. Check the light sensor. See «AUTOMATIC HEADLIGHTS & LIGHTING SYSTEMS»(ref-154254) article under HEADLIGHTS in ACCESSORIES & EQUIPMENT. If the results are OK, go to the next step. If the results are not good, replace the faulty light sensor. See «INSTRUMENT PANEL»(ref-154166) article in ACCESSORIES & EQUIPMENT.
2. Check the wiring harness and connector between the light sensor and anti-theft ECU. If the results are OK, replace the faulty anti-theft ECU located behind the lower finish panel of the instrument panel. See «INSTRUMENT PANEL»(ref-154166) article in ACCESSORIES & EQUIPMENT. If the results are not good, repair or replace the faulty wiring harness or connector. See «HEADLIGHTS»(ref-141321-S05699451662002121100000) in SYSTEM WIRING DIAGRAMS article.

Detecting Condition - No communication from the ECM for more than 10 seconds. (Scheme 10)

Trouble Area

1. ECM.
2. Wiring Harness.

1. Check that the engine starts normally. With this inspection, the ECM can be diagnosed if it works normally or not. If the results are OK, go to the next step. If the results are not good, replace the faulty ECM. See «ENGINE CONTROL MODULE (ECM)»(ref-154087-S41315086562003050200000) under REMOVAL & INSTALLATION.
2. Disconnect the connector of the body ECU, connector E4 of the ECM and connector A12 of the A/C ECU. (Scheme 13) Check the continuity between 12-pin connector terminal 7 (MPX1) of the body ECU and connector E4 terminal 20 (MPX2) of the ECM. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000). Check continuity between connector E4 terminal 21 (MPX1) of the ECM and connector A12 terminal 1 (MPX-) of the A/C ECU. If there is continuity in the wiring harness of both (A) and (B), or either (A) or (B), replace the faulty ECM. See «ENGINE CONTROL MODULE (ECM)»(ref-154087-S41315086562003050200000) under REMOVAL & INSTALLATION. If there is not continuity, repair or replace the faulty wiring harness. If there is an open in the wiring harness of either (A) or (B), repair it. See «COMPUTER DATA LINES»(ref-141321-S05161498362002121100000) in SYSTEM WIRING DIAGRAMS article.

Scheme 13

This DTC is output when communication stops between A/C ECU and body ECU. (Scheme 10)

Detecting Condition - No communication from the ECU for more than 10 seconds.

Trouble Area

1. A/C ECU.
2. Wiring Harness.

Disconnect connector C9 of the combination meter, connector A12 or A13 of the A/C ECU and connector E4 of the ECM. (Scheme 14)

1. Check continuity between connector A12 terminal 1 (MPX-) of the A/C ECU and connector E4 terminal 21 (MPX1) of the ECM. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000) .
2. Check continuity between connector C9 terminal 21 (MPX-) of the combination meter and connector A13 terminal 10 (MPX+) of the A/C ECU.

If there is continuity in the wiring harness of both (A) and (B), (A) or either (B), replace the faulty A/C ECU located in the A/C control with radio receiver assembly. See

INSTRUMENT PANEL

article in ACCESSORIES & EQUIPMENT. If there is not continuity, repair or replace the faulty wiring harness. If there is an open in the wiring harness of either (A) or (B), repair it. See

BODY COMPUTER

in SYSTEM WIRING DIAGRAMS article.

Scheme 14

This DTC is output when communication stops between the anti-theft ECU and body ECU. (Scheme 10)

Detecting Condition - No communication from the anti-theft ECU for more than 10 seconds.

Trouble Area

1. Anti-Theft ECU.
2. Wiring Harness.

1. Check the anti-theft ECU. Check that the operation of the anti-theft function is normal. With this inspection, the anti-theft ECU can be diagnosed if it works normally or not. If the results are OK, go to the next step. If the results are not good, replace the faulty anti-theft ECU located behind the lower finish panel. See «INSTRUMENT PANEL»(ref-154166) article in ACCESSORIES & EQUIPMENT.
2. Disconnect connector B6 of the body ECU, connector C9 of the combination meter and connector T6 of the anti-theft ECU. (Scheme 15) Check the continuity between connector T6 terminal 8 (MPX2) of the anti-theft ECU and connector C9 terminal 20 (MPX+) of the combination meter ECU. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000). Check the continuity between connector B6 terminal 5 (MPX2) of the body ECU and connector T6 terminal 7 (MPX1) of the anti-theft ECU. If there is continuity in the wiring harness of both (A) and (B), or either (A) or (B), replace the faulty anti-theft ECU located behind the lower finish panel of the instrument panel. See «INSTRUMENT PANEL»(ref-154166) article in ACCESSORIES & EQUIPMENT. If there is not continuity, repair or replace the faulty wiring harness. If there is an open in the wiring harness of either (A) or (B), repair it. See «ANTI-THEFT»(ref-141321-S32368335392002121100000) in SYSTEM WIRING DIAGRAMS article.

Scheme 15

This DTC is output when communication stops between combination meter ECU and body ECU. (Scheme 10)

Detecting Condition - No communication between combination meter ECU and body ECU.

Trouble Area

1. Combination Meter ECU.
2. Wiring Harness.

1. Check the combination meter ECU. Start the engine and check that the speedometer and tachometer operate normally. With this inspection, the combination meter ECU can be diagnosed if it works normally or not. If the results are OK, go to the next step. If the results are not good, replace the faulty combination meter ECU. See «INSTRUMENT PANEL»(ref-154166) article in ACCESSORIES & EQUIPMENT.
2. Disconnect connector A13 of the A/C ECU, connector C9 of the combination meter ECU, connector B6 of the body ECU and connector T6 of the anti-theft ECU, if equipped. (Scheme 16) Check the continuity between connector A13 terminal 10 (MPX+) of the A/C ECU and connector C9 terminal 21 (MPX-) of the combination meter ECU. See «CONNECTOR IDENTIFICATION»(ref-154087-S04934954892003050200000). On vehicles without anti-theft system, check continuity between connector C9 terminal 9 (MPX+) of the combination meter and connector B6 terminal 5 (MPX2) of the body ECU. On vehicles with anti-theft system, check continuity between connector C9 terminal 20 (MPX+) of the combination meter and connector T6 terminal 8 (MPX2) of the anti-theft ECU. If there is continuity in the wiring harness of both (A) and (B), or either (A) or (B), replace the faulty combination meter ECU. See «INSTRUMENT PANEL»(ref-154166) article in ACCESSORIES & EQUIPMENT. If there is not continuity, repair or replace the faulty wiring harness. If there is an open in the wiring harness of either (A) or (B), repair it. See «INSTRUMENT CLUSTER»(ref-141321-S27868137932002121100000) in SYSTEM WIRING DIAGRAMS article.

Scheme 16