DTC P0120: Throttle Position (TP) Sensor: Procedure

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 2 engine ground bolts located on intake manifold, near fuel injectors. Disconnect TP sensor harness connector. See Fig 1. Turn ignition on. Measure voltage between ground and TP sensor harness connector terminal No. 1 (Red wire). If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, repair open or short in Red wire and retest system.
3. Turn ignition off. Check continuity between engine ground and TP sensor harness connector terminal No. 3 (Black wire). Also check circuit for short to voltage. See WIRING DIAGRAMS article. Repair circuit as necessary and retest system. If ground circuit is okay, go to next step.
4. Disconnect ECM harness connector. See Figure. Check continuity of Yellow wire between ECM harness connector terminal No. 23 and TP sensor harness connector terminal No. 2. See Figure. 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.
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 by backprobing, with throttle in specified positions. See THROTTLE POSITION (TP) 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. If malfunction "A" or "C" was duplicated, go to step  12. If malfunction "B" was duplicated, go to next step.
CAUTION: Do not use ECM ground terminals when measuring voltage.
8. Start engine and warm to normal operating temperature. Measure voltage between ground and ECM terminal No. 47 (MAF sensor signal) by backprobing, with engine at specified speeds. See MASS AIRFLOW SENSOR VOLTAGE  table under DTC P0100: MASS AIRFLOW (MAF) SENSOR.
9. 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  8. If voltage is still not as specified, replace MAF sensor and retest system. If voltage is now as specified, go to next step.
10. Ensure engine is at normal operating temperature. Measure voltage between ground and ECM terminals No. 40 and 41 (CMP sensor signal) by backprobing, with engine at specified speeds. See PIN VOLTAGE CHARTS article. If voltage or waveforms are as specified, go to next step. If voltage or waveforms are not as specified, replace distributor assembly and retest system.
11. Check fuel injectors and circuits. See SYSTEM & COMPONENT TESTING article. Repair injectors or circuits as necessary and retest system. If no problems are found, 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 (TP) SENSOR VOLTAGE

Throttle Position	Volts
Fully Closed	.15-.85
Partially Open	.15-.85 To 3.5-4.7
Fully Open	3.5-4.7

Fig 1: Locating Throttle Position (TP) Sensor Harness Connector

Courtesy of NISSAN MOTOR CO., U.S.A.