| WARNING | Read service precautions before proceeding with service procedure. See SERVICE PRECAUTIONS . |
| CAUTION | If Engine Control Module (ECM) replacement is instructed in following test, always ensure ECM electrical connectors and ground circuits are okay. If either are defective, repair and repeat testing to confirm ECM malfunction. |
Circuit Description
Constant battery voltage is supplied to BATT terminal at ECM as the back-up power source. DTC is set when open in back-up power source is detected. Possible causes are
- Back-up power source circuit is open.
- Defective ECM.
Diagnostic Aids
If DTC P1600 exists, the ECM will not store any other DTCs. Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.