LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2004 >> Matrix Base, FWD, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 34 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0120: Throttle (TP)/Pedal Position Sensor Switch "A" Circuit Malfunction >> Diagnosis & Repair
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Turn scan tool on. Using scan tool, monitor throttle valve opening percentage. Opening percentage should be about 10 percent with fully closed throttle. Depress accelerator pedal to floor (WOT). Opening percentage should be about 75 percent. If percentages are within specification, check all connections. Problem may be intermittent. If percentages are not within specification, go to next step.
  2. Disconnect TP sensor harness connector. Turn ignition on. Using voltmeter, measure voltage between ground and Yellow/Black wire at TP sensor harness connector. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, go to step  5.
  3. Turn ignition off. Using ohmmeter, measure resistance between terminals No. 1 (Yellow/Black wire) and No. 2 (Brown wire) at TP sensor component connector. Resistance should be 2500-5900 ohms. Measure resistance between terminals No. 2 (Brown wire) and No. 3 (Blue/White wire). Resistance should be 200-6300 ohms with throttle fully closed, and 2000-10,200 ohms with throttle fully open. If any readings are not within specification, replace TP sensor. If all readings are within specification, go to next step.
  4. Connect TP sensor harness connector. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals No. 23 (Blue/White wire) and No. 18 (Brown wire) at ECM E8 connector. See Figure. Voltage should be .3-1.0 volt with throttle fully closed, and 2.7-5.2 volts with throttle fully open (WOT). If voltages are as specified, replace ECM and retest system. If voltages are not as specified, locate and repair open or short in Blue/White wire between TP sensor and ECM E8 connector.
  5. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector E8, measure voltage between terminals No. 2 (Yellow/Black wire) and No. 18 (Brown wire). If voltage is 4.5-5.5 volts, locate and repair open in Yellow/Black wire between TP sensor and ECM E8 connector. If voltage is not 4.5-5.5 volts, replace ECM and retest system.
scientia non olet · About LEMON Manuals