Note. For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.
| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article. |
Circuit Description
Battery positive voltage is supplied to terminal BATT of the ECM even when the ignition switch is OFF for use by the DTCs memory and air-fuel ratio adaptive control value memory. DTC is set when an open is detected in back-up power circuit. (Scheme 160) Possible causes are
- Open in back-up power source circuit.
- Faulty ECM.
Scheme 160
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.
Scheme 161
Scheme 162
Scheme 163
- Measure the voltage between the terminal BATT of ECM E6 connector and terminal E1 of ECM E3 connector. (Scheme 161) If 9-14 volts are present, check and replace ECM. If 9-14 volts are not present, go to next step.
- Remove EFI fuse from the engine room No. 1 relay block. (Scheme 162) Check continuity of fuse. Replace fuse as necessary. If fuse is okay, go to next step.
- Disconnect the battery positive terminal. Disconnect the ECM E6 connector. (Scheme 163) Check the continuity between the wire harness side connectors. See «BATTERY/ECM CONTINUITY CHECK»(ref-151781-S02834862552003030300000) table. If continuity is to specification, replace engine room relay block. If continuity is not to specification, repair or replace harness and connector. BATTERY/ECM CONTINUITY CHECK Terminals No. Specification Battery Positive Terminal - BATT (E6-4) Continuity Battery Positive Terminal Or BATT (E6-4) - E1 (E3-7) No Continuity