DTC P1125: THROTTLE CONTROL MOTOR CIRCUIT Toyota Tundra I

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. When this occurs, throttle valve is controlled by throttle cable connected to accelerator pedal. Possible causes are

1. Throttle control motor circuit is open or shorted.
2. Defective throttle control motor.
3. 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 289

Scheme 290

1. Remove glove box and heater duct (if necessary) for access to ECM with electrical connectors still installed on ECM. see scheme 2 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 E6 and No. 7 (White wire; M- circuit) or No. 8 (Red 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 4 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 289) 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.
2. Disconnect electrical connector at throttle control motor located on side of throttle body. (Scheme 290) Using ohmmeter, check resistance between terminals No. 1 and 2 on electrical connector on throttle control motor. (Scheme 290) Resistance should be.3-100.0 ohms at 68°F (20°C). If resistance is within specification, go to next step. If resistance is not within specification, replace throttle control motor. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
3. Check for open and short in White and Red wires and electrical connectors between throttle control motor and ECM. See WIRING DIAGRAMS article. If wiring harness and electrical connectors are okay, replace ECM. If wiring harness or electrical connector is defective, repair as necessary.