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DTC P0505: IDLE AIR CONTROL SYSTEM MALFUNCTION Lexus SC II

Testing & Diagnostics 9 illustrations ~746 words

Note. For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.

CAUTIONIf ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article.

Circuit Description

Idle speed is controlled by Electronic Throttle Control System (ETCS). ETCS is composed of throttle motor, magnetic clutch, TP sensor, accelerator pedal position sensor, ECM and throttle body. ECM controls throttle motor to adjust throttle valve opening angle. DTC P0505 is set if idle speed continues to vary greatly from target speed. Possible causes are

  1. Faulty ETCS.
  2. Leaking air intake system.
  3. Faulty PCV hose connection.
  4. Faulty ECM.

Diagnostic Aids

Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.

Scheme 151

Scheme 151: Diagnosis & Repair
Scheme 151: Diagnosis & Repair

Scheme 152

Scheme 152
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Scheme 153

Scheme 153
Scheme 153

Scheme 154

Scheme 154
Scheme 154

Scheme 155

Scheme 155
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Scheme 156

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Scheme 157

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Scheme 159

Scheme 159
Scheme 159
  1. Retrieve trouble codes. See «RETRIEVING DIAGNOSTIC TROUBLE CODES»(ref-151781-S29975222372003010800000) under SELF-DIAGNOSTIC SYSTEM. If only DTC P0505 is displayed, go to next step. If other codes are displayed, diagnose and repair those codes first and retest.
  2. Check for loose, damaged or cracked air intake hose between throttle body and air cleaner. Check for loose or damaged dipstick or oil fill cap. Repair as necessary. If all components are okay, go to next step.
  3. Check connection of PCV hose. Repair or replace as necessary. If okay, go to next step.
  4. Disconnect the throttle control motor connector. Measure the resistance between the terminals No. 1 and 2 of throttle control motor. (Scheme 151) If resistance is.3-100 ohms at 68°F (20°C), go to next step. If resistance is not.3-100 ohms at 68°F (20°C), replace throttle body assembly.
  5. Disconnect T2 throttle control motor 2-pin connector. (Scheme 152) Disconnect ECM E2 connector. Check continuity between wire harness side of connectors. (Scheme 153) See «THROTTLE CONTROL MOTOR/ECM CONTINUITY CHECK»(ref-151781-S33550803342003030300000) table. If continuity is to specification, go to next step. If continuity is not to specification, repair or replace harness or connector as necessary. THROTTLE CONTROL MOTOR/ECM CONTINUITY CHECK Terminals No. Specification (T2-2) - M+ (E2-3) Continuity (T2-1) - M- (E2-2) Continuity (T2-2) Or M+ (E2-3) - E1 (E3-7) No Continuity (T2-1) Or M- (E2-2) - E1 (E3-7) No Continuity
  6. Disconnect the throttle position sensor connector. Measure resistance between throttle position sensor terminals No. 3 and 6. (Scheme 154) Resistance should be 1.25-2.35 ohms at 68°F (20°C). If resistance is to specification, go to next step. If resistance is not to specification, replace throttle position sensor.
  7. Disconnect T2 throttle position sensor 4-pin connector. (Scheme 155) Disconnect ECM E2 connector. Check continuity between the wire harness side connectors. (Scheme 156) See «THROTTLE POSITION SENSOR/ECM CONTINUITY CHECK»(ref-151781-S04457200602003030300000) table. If continuity is to specification, go to next step. If continuity is not to specification, repair or replace harness and connector as necessary. THROTTLE POSITION SENSOR/ECM CONTINUITY CHECK Terminals No. Specification (T2-3) - VC (E2-23) Continuity (T2-4) - VTA2 (E2-24) Continuity (T2-5) - VTA (E2-25) Continuity (T2-6) - ETA (E2-22) Continuity (T2-3) Or VC (E2-23) - E1 (E3-7) No Continuity (T2-4) Or VTA2 (E2-24) - E1 (E3-7) No Continuity (T2-5) Or VTA (E2-25) - E1 (E3-7) No Continuity (T2-6) Or ETA (E2-22) - E1 (E3-7) No Continuity
  8. Disconnect the accelerator pedal position sensor connector. Measure the resistance between the terminals of the accelerator pedal position sensor. (Scheme 157) See «ACCELERATOR PEDAL POSITION SENSOR RESISTANCE»(ref-151781-S41390061002003030300000) table. If resistance is to specification, go to next step. If resistance is not to specification, replace accelerator pedal rod assembly. ACCELERATOR PEDAL POSITION SENSOR RESISTANCE Terminals No. Specification EP1 (1) - VCP1 (4) 1.5-60 Ohms At 68°F (20°C) EP2 (3) - VCP2 (5) 1.5-60 Ohms At 68°F (20°C)
  9. Disconnect A14 6-pin accelerator pedal position sensor connector. (Scheme 158) Disconnect ECM E5 connector. (Scheme 159) Check continuity between the wire harness side connectors. See «ACCELERATOR PEDAL POSITION SENSOR/ECM CONTINUITY CHECK»(ref-151781-S28917975002003030300000) table. If continuity is to specification, check and replace ECM. If continuity is not to specification, repair or replace harness and connector. ACCELERATOR PEDAL POSITION SENSOR/ECM CONTINUITY CHECK Terminals No. Specification EP1 (A14-1) - EPA(E5-34) Continuity VCP1 (A14-4) - VCPA (E5-35) Continuity VPA1 (A14-5) - VPA (E5-33) Continuity EP2 (A14-3) - EPTK (E5-26) Continuity VCP2 (A14-6) - VPTK (E5-27) Continuity VPA2 (A14-2) - VPTA (E5-32) Continuity EP1 (A14-1) Or EPA (E5-34) - E1 (E3-7) No Continuity VCP1 (A14-4) Or VCPA (E5-35) - E1 (E3-7) No Continuity VPA 1 (A14-5) Or VPA (E5-33) - E1 (E3-7) No Continuity EP2 (A14-3) Or EPTK (E5-26) - E1 (E3-7) No Continuity VCP2 (A14-6) Or VPTK (E5-27) - E1 (E3-7) No Continuity VPA2 (A14-2) Or VPTA (E5-32) - E1 (E3-7) No Continuity

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