Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSTOYOTA2004CELICA GT, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 32 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P1120: ACCELERATOR PEDAL POSITION (APP) SENSOR CIRCUITDIAGNOSIS & REPAIR (USING OBD-II SCAN TOOL)
2004 Toyota Celica GT, Standard
Diagnosis & Repair (Using OBD-II Scan Tool)
2004 Toyota Celica GT, StandardSECTION Diagnosis & Repair (Using OBD-II Scan Tool)
WARNING: This page is about a different car, the 2002 Lexus LX 470. However, it is still accessible from the selected car via links, so may be relevant.
- Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between terminals No. 2 (Blue/Red wire) and No. 18 (Brown/White wire) at ECM harness connector E7. See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM.
- Using DVOM, backprobe ECM harness connector and measure voltage between terminals No. 18 (Brown/White wire) and No. 21 (Red wire) at ECM harness connector E7. With fully closed throttle, voltage should be .3-.9 volt. With fully open throttle, voltage should be 3.2-4.8 volts. Using DVOM, backprobe ECM harness connector and measure voltage between terminals No. 18 (Brown/White wire) and No. 9 (Red/Black wire) at ECM harness connector E7. With fully closed throttle, voltage should be 1.8-2.7 volts. With fully open throttle, voltage should be 4.7-5.1 volts. If voltage readings are as specified, replace ECM. If voltage readings are not as specified, go to next step.
- Check APP sensor. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - LX470 article. If problem exists, replace APP sensor. If problem does not exist, repair open or short in wiring between ECM and APP sensor. See WIRING DIAGRAMS article.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.