Diagnostic Procedure

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

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 article in ACCESSORIES & EQUIPMENT.
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. See Fig 1.
1. 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 .
2. 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 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 in SYSTEM WIRING DIAGRAMS article.

Fig 1: Checking Combination Meter ECU Communication Circuit