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Home >> Nissan-Datsun >> 2003 >> Sentra Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 41 (Engine Controls - Self-Diagnostics - Quest) >> Diagnostic Tests >> DTC P0120: Throttle Position Sensor >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.
  1. If malfunction "A" or "B" was duplicated, go to next step. If malfunction "C" was duplicated, adjust TP sensor. See ON-VEHICLE ADJUSTMENTS article. Check air intake duct and vacuum hoses for leaks or disconnection. Reconnect or repair as necessary and retest system. If no problems are found, go to next step.
  2. Turn ignition off. Loosen and retighten engine ground bolts. See Figure. Disconnect TP sensor harness connector. See Fig 1. Turn ignition on. Measure voltage between ground and TP sensor harness connector terminal No. 1 (Brown wire). If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, repair open or short in Brown wire between TP sensor and ECM, then retest system.
  3. Turn ignition off. Check continuity between ground and TP sensor harness connector terminal No. 3 (Black/Yellow wire). Continuity should exist. Also, check circuit for short to voltage. See WIRING DIAGRAMS article. Repair circuit as necessary and retest system. If circuit is okay, go to next step.
  4. Turn ignition off. Disconnect ECM harness connector. See Figure. Check continuity of Red wire between ECM harness connector terminal No. 23 and TP sensor harness connector terminal No. 2. See Figure and Fig 2 . Continuity should exist. Also, check circuit for short to ground and short to voltage. Repair circuit as necessary and retest system. If circuit is okay, go to next step.
    5. CAUTION: DO NOT use ECM ground terminals when measuring voltage.
  5. Reconnect all harness connectors. Start engine and warm to normal operating temperature. Stop engine and turn ignition on. Measure voltage between ground and ECM terminal No. 23 (Red wire) by backprobing, with throttle in specified positions. See THROTTLE POSITION SENSOR VOLTAGE  table. If voltage is not as specified, go to next step. If voltage is as specified, go to step  7.
  6. Adjust closed throttle position switch. See ON-VEHICLE ADJUSTMENTS article. Repeat step  5. If voltage is now as specified, go to next step. If voltage is still not as specified, replace TP sensor and retest system.
  7. Start engine and warm to normal operating temperature. Measure voltage between ground and MAF sensor signal circuit at ECM terminal No. 61 (Green wire), with engine at specified speeds. See MASS AIRFLOW SENSOR VOLTAGE  table under DTC P0100: MASS AIRFLOW SENSOR. Go to next step.
  8. If voltage is as specified, go to next step. If voltage is not as specified, disconnect and reconnect MAF sensor harness connector and repeat step  7. If voltage is still not as specified, replace MAF sensor and retest system. If voltage is now as specified, go to next step.
    9. CAUTION: DO NOT use ECM ground terminals when measuring voltage.
  9. Ensure engine is at normal operating temperature. Measure voltage between ground and CMP sensor signal circuit at ECM terminals No. 44, 48 (both White wires) and No. 49 (Orange wire) by backprobing. See PIN VOLTAGE CHARTS article for specifications. If voltages or waveforms are as specified, go to next step. If voltages or waveforms are not as specified, replace CMP sensor and retest system.
  10. Turn ignition off. Disconnect each fuel injector harness connector. Measure resistance between each fuel injector terminals (component side). Resistance should be 10-14 ohms at 77°F (25°C). If resistance is as specified, go to next step. If resistance is not as specified, replace defective fuel injector(s) as necessary and retest system.
  11. Turn ignition off. Disconnect 42-pin super multiple junction connector F-12 from firewall. Check continuity between ground and engine control harness connector terminal No. 8A (Black/Red wire). See Figure. Continuity should exist. Also, check circuit for short to voltage. Repair circuit as necessary and retest system. If circuit is okay, go to next step.
  12. No problem is indicated at this time. Problem may be intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
THROTTLE POSITION SENSOR VOLTAGE

Throttle Position Volts
Fully Closed .15-.85
Between Fully Closed & Fully Open .15-.85 To 3.5-4.7
Fully Open 3.5-4.7
Fig 1: Locating TP Sensor & TP Switch Harness Connectors
G00042089Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: Identifying TP Sensor & TP Switch Terminals (Component Side Shown)
G00014348Courtesy of NISSAN MOTOR CO., U.S.A.
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