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Home >> Infiniti >> 2003 >> QX4 4WD >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0122: Throttle Position Sensor Circuit - Low Input Or DTC P0123: Throttle Position Sensor Circuit - High Input >> Diagnostic Procedure
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Diagnostic Procedure

  1. Turn ignition off. Loosen and retighten 2 engine ground bolts. See Figure. Go to next step.
  2. Disconnect TPS 3-pin harness connector. Turn ignition on. Measure voltage between ground and TPS harness connector terminal No. 1. See Figure. Voltage should be 5 volts. If voltage is as specified, go to next step. If voltage is not as specified, repair open, short to ground or short to voltage in harness or connectors.
  3. Turn ignition off. Check continuity in Black/Pink wire between ground and TPS harness connector No. 3. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Continuity should exist. Also check for short to voltage. If problem is found, go to next step. If no problem is found, go to step  5.
  4. Check for open or short in circuits between ECM and TPS. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Check for open or short in circuits between ECM and TPS. If problem is found, repair as necessary.
  5. Turn ignition off. Disconnect ECM 116-pin harness connector. ECM is located behind instrument panel lower cover. See Figure. Check continuity in Red wire between ECM harness connector terminal No. 91 and TPS harness connector terminal No. 2. See Figure and Figure . Continuity should exist. Also check circuit for short to ground or short to voltage. If no problem is found and testing is being done with a CONSULT-II, connect harness connectors and go to next step. If no problem is found and testing is being done with a generic scan tool, connect harness connectors and go to step  7. If problem is found, repair as necessary.
  6. Start engine and warm to normal operating temperature. Turn ignition off, and then back to ON position. On CONSULT-II, select DATA MONITOR mode. Observe THRTL POS SEN parameter a specified conditions. See CHECKING THROTTLE POSITION SENSOR VOLTAGES table. If TPS parameters are as specified, go to step  9. If TPS parameters are not as specified, go to step  8.
    CHECKING THROTTLE POSITION SENSOR VOLTAGES

    Throttle Valve Position Volts
    Fully Closed .15-.85
    Partially Open (1)
    Fully Open 3.5-4.7
    (1) Voltage should change smooth and steady, from lower to upper voltage value, with no glitches as throttle valve is opened.
    7. NOTE: TPS must remain on vehicle for this test.
  7. Start engine and warm to normal operating temperature. Turn ignition off, and then back to ON position. Backprobbing at ECM, measure voltage between ground and ECM harness connector terminal No. 91 (Red wire). See CHECKING THROTTLE POSITION SENSOR VOLTAGES table. If voltage is as specified, go to step  9. If voltage is not as specified, go to next step.
  8. Check TPS adjustment. See BASIC INSPECTION under THROTTLE POSITION SENSOR, IGNITION TIMING & IDLE SPEED in ON-VEHICLE ADJUSTMENTS article. If TPS adjusts as specified, go to next step. If TPS does not adjust as specified, replace TPS. See THROTTLE POSITION SENSOR under SENSORS & SWITCHES in REMOVAL & INSTALLATION article.
    9. CAUTION: DO NOT use ECM ground terminals when measuring voltage.
  9. Start engine and warm to normal operating temperature. Backprobing, measure voltage between ground and ECM harness connector terminal No. 61 (Orange wire), with engine at specified speeds. See CHECKING MASS AIR FLOW SENSOR VOLTAGE  table. If voltage is as specified, connect disconnected components and go to next step. If voltage is not as specified, disconnect and reconnect MAF sensor harness connector and repeat test. If voltage is still not as specified, replace MAF sensor.
    CHECKING MASS AIR FLOW SENSOR VOLTAGE

    Condition Volts
    Ignition On, Engine Off About 1.0
    Idle 1.2-1.8
    2500 RPM 1.6-2.2
    Idle To 4000 RPM (1) 1.2-1.8 To About 4.0
    (1) Voltage should change smooth and steady, from lower to upper voltage value, with no glitches as engine speed is increased.
  10. Check CKP sensor (POS). Perform DTC confirmation for DTCs P0335 and P1336, go to DTC P0335  and DTC P1336  . If no problem is found, go to next step. If problem is found, replace CKP sensor (POS). See CRANKSHAFT POSITION SENSOR under SENSORS & SWITCHES in REMOVAL & INSTALLATION article.
  11. Check CKP sensor (REF). Perform DTC confirmation for DTCs P1335, go to DTC P1335 . If no problem is found, go to next step. If problem is found, replace CKP sensor (REF). See CRANKSHAFT POSITION SENSOR under SENSORS & SWITCHES in REMOVAL & INSTALLATION article.
  12. Check resistance of fuel injectors. See FUEL CONTROL under FUEL SYSTEM in SYSTEM & COMPONENT TESTING article. If no problem is found, go to next step. If problem is found, replace suspect fuel injector. See FUEL INJECTORS & FUEL TUBES under FUEL SYSTEMS in REMOVAL & INSTALLATION article.
  13. No problem is indicated at this time. Problem may be intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
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