| 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
Electronic Throttle Control System (ETCS) uses throttle control motor to operate throttle valve. Throttle valve opening is detected by Throttle Position (TP) sensor which delivers input signals to ECM. ECM uses input signals and controls the throttle control motor to provide proper throttle valve opening in response to driving conditions. DTC is set if a throttle control motor current or output duty is not within specified range. If DTC P1125 exists, ECM will turn off the power to throttle control motor and throttle valve is closed by the return spring. Possible causes are
- Throttle control motor circuit is open or shorted.
- Defective throttle control motor.
- Defective ECM.
Diagnostic Aids
Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.
Scheme 323
Scheme 324
- Remove glove box for access to ECM with electrical connectors still installed on ECM. see scheme 3 Waveform pattern should be checked for throttle control motor M+ and M- circuits at ECM. Connect oscilloscope between terminal No. 17 (Brown wire) at ECM electrical connector E8 and No. 7 (Pink wire; M- circuit) or No. 8 (Blue wire; M+ circuit) at ECM electrical connector E7. This is the E1, M- and M+ terminals on ECM. For ECM electrical connector terminal identification see scheme 7 Start engine and allow engine to idle. Note M- and M+ waveform pattern with engine idling. Ensure M- and M+ waveform patterns are properly displayed. (Scheme 323) Ensure engine is idling when checking waveform pattern, as waveform pattern will change with throttle opening. If any waveform pattern is not as shown, shut engine off. Go to next step. If both waveform patterns are as shown, shut engine off. Replace ECM.
- Check throttle control motor. See THROTTLE BODY under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If throttle control motor is okay, go to next step. If throttle control motor is defective, replace throttle body with throttle control motor as an assembly. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
- Check for open and short in wiring harness and electrical connectors between throttle control motor and ECM. See WIRING DIAGRAMS article. Throttle control motor is located on side of throttle body. (Scheme 324) If wiring harness and electrical connectors are okay, replace ECM. If wiring harness or electrical connector is defective, repair as necessary.