| 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 article in GENERAL INFORMATION. |
Note. If DTCs P0110, P0115, P0120, P0450 and P1120 are output together, check circuit E2 (Brown/White wire) between terminal No. 18 at ECM harness connector E7 and splice E4. Repair as necessary. See appropriate wiring diagram in WIRING DIAGRAMS article.
Circuit Description
APP sensor is located on throttle body and has 2 variable resistors integral to APP sensor. APP sensor monitors accelerator position and is connected with accelerator pedal by accelerator wire. APP sensor signal voltage (0-5 volts) to ECM changes in proportion to accelerator pedal opening angle. ECM controls throttle motor based on APP sensor voltage signals. If DTC P1120 is present, ECM turns off power to throttle motor and magnetic clutch and throttle valve is fully closed by the return spring. When this occurs, opening angle of throttle valve is controlled by accelerator pedal by means of a throttle cable. DTC is set when ECM detects voltage is out of range on VPA or VPA2 circuits. Possible causes are
- APP sensor circuit is open or shorted.
- Defective APP sensor.
- Defective ECM.
Diagnostic Aids
After confirming DTC P1120, use scan tool to access CURRENT DATA to confirm APP sensor voltage with throttle open and closed. If voltage displayed on scan tool for ACCEL POS and ACCEL POS #2 is always zero volts, VC circuit may be open. If voltage displayed on scan tool for ACCEL POS is always zero volts and voltage display for ACCEL POS #2 is 1.8-2.7 volts with fully closed throttle and 4.7-5.1 volts with fully open throttle, VPA circuit may be open or shorted. If voltage displayed on scan tool for ACCEL POS #2 is always zero volts and voltage display for ACCEL POS is .3-.9 volt with fully closed throttle and 3.2-4.8 volts with fully open throttle, VPA2 circuit may be open or shorted. If voltage displayed on scan tool for ACCEL POS and ACCEL POS #2 is always 5 volts, E2 circuit may be open. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.