Engine Control System Tests W/codes - 1.6L: Diagnosis Toyota Corolla VII

MALFUNCTION INDICATOR LIGHT (MIL) INSPECTION

Note. The CHECK engine light located on instrument cluster is known as Malfunction Indicator Light (MIL). Inspect MIL to ensure it is operational and will come on if a Diagnostic Trouble Code (DTC) is set.

1. Turn ignition on with engine off. MIL should come on and remain on. If MIL does not come on, check bulb circuit on instrument cluster and wiring circuit between MIL and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. See «ECM LOCATION»(ref-21945-S14248354262001010300000) .
2. Start engine and ensure MIL goes off. If MIL remains on with engine running, a malfunction is detected. Proceed to RETRIEVING DIAGNOSTIC TROUBLE CODES.

TESTING PROCEDURE

To ensure correct diagnosis and repair, testing should be done in the following sequence

1. Record Customer Complaint Ensure all customer complaints or observations are recorded. Test drive vehicle with customer when necessary for malfunction verification.
2. Retrieve Diagnostic Trouble Codes Connect appropriate scan tester. Retrieve codes and record any freeze-frame data (if applicable). See «RETRIEVING DIAGNOSTIC TROUBLE CODES»(ref-21945-S17851880562001010300000) .
3. Clear Trouble Codes Clear codes. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-21945-S31796302082001010300000) .
4. Visual Inspection Inspect all connectors of suspect circuit or component. Ensure all connections are clean and tight.
5. Confirm Symptoms & Trouble Codes Perform road test. Determine if original symptoms are still present. Retrieve codes.
6. Diagnose & Repair Diagnostic Trouble Codes Perform diagnosis and repair procedures as necessary. If no codes are present, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).
7. Verification Procedure After repairs have been completed, clear all diagnostic trouble codes. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-21945-S31796302082001010300000) . Perform road test. Ensure no codes are present and all symptoms and/or complaints have been repaired.

RETRIEVING DIAGNOSTIC TROUBLE CODES

Note. Diagnostic Trouble Codes (DTCs) may be retrieved using Toyota scan tester or On-Board Diagnostic (OBD-II) scan tester that complies with SAE standard J-1978. Toyota scan tester or OBD-II scan tester may be operated in NORMAL mode when retrieving trouble codes. Only Toyota scan tester may be used in CHECK mode when retrieving DTCs.

NORMAL mode is used to retrieve DTCs from Engine Control Module (ECM). CHECK mode is used to check for DTCs when operating vehicle to simulate conditions in which DTC was set. CHECK mode contains a higher sensing ability to detect malfunctions. CHECK mode helps determine malfunctions caused by poor electrical connections, which are difficult to determine using NORMAL mode.

Note. If using Toyota scan tester, when ignition switch is turned from ON to ACC or OFF position or scan tester is switched from NORMAL mode to CHECK mode, all DTCs and freeze-frame data will be erased. DO NOT switch modes until all DTCs and freeze-frame data are recorded.

CLEARING DIAGNOSTIC TROUBLE CODES

1. After performing repairs, clear ECM memory of all stored Diagnostic Trouble Codes (DTCs) and freeze-frame data. DTCs and freeze-frame data may be cleared by using scan tester and scan tester manufacturer's instructions. NOTE: If using Toyota scan tester, DTCs and freeze-frame data may be cleared by switching from CHECK mode to NORMAL mode or from NORMAL mode to CHECK mode.
2. DTCs and freeze-frame data may also be cleared by removing EFI fuse from fuse block, located in engine compartment. DTCs and freeze-frame data may also be cleared by disconnecting negative battery cable. However, other memory functions (clock, radio, alarm, seats, etc.) will be cancelled and must be reset.

Note. Not all codes listed in the following table are used on every vehicle.

TROUBLE CODE IDENTIFICATION

TROUBLE CODE TEST DRIVE CONFIRMATION

1. On certain Diagnostic Trouble Codes (DTCs), once DTC has been cleared from ECM memory, a DTC test drive confirmation test can be performed to verify repairs made and that DTC does not reset. The test drive confirmation test will duplicate the conditions required to set specified DTCs.
2. Test drive confirmation test lists the procedure to be performed to check that DTC does not reset. Test drive confirmation tests apply only to specific DTCs. Test drive confirmation test will be included with proper DTC circuit test.

DLC3 INSPECTION

1. If scan tester displays UNABLE TO CONNECT TO VEHICLE when scan tester is connected, try scan tester on another vehicle. If scan tester operates on another vehicle, go to next step. If scan tester does not operate on another vehicle, problem is probably with scan tester.
2. Check DLC3 for loose or damaged terminals. Ensure DLC3 terminals are in correct position in connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If connector and terminals are okay, go to next step.
3. Check voltage and resistance between ground and specified terminal on DLC3. See «DLC3 VOLTAGE & RESISTANCE SPECIFICATIONS»(ref-21945-S03519231572001010300000) table. (Scheme 10) If voltage and resistance readings are not as specified, check wiring circuit. See appropriate wiring diagram in WIRING DIAGRAMS article.

Note. Terminal No. 2 on DLC3 provides the pulse generation during the information transmission from the Engine Control Module (ECM).

DLC3 VOLTAGE & RESISTANCE SPECIFICATIONS

Scheme 10

Diagnosis & Repair

If any other codes other than DTC P0106 are displayed, diagnose and repair those codes first. If only DTC P0106 is displayed, replace MAP sensor.

1. Connect scan tester to DLC3 connector. (Scheme 10) Turn ignition on. Turn on scan tester. Monitor IAT sensor temperature. If temperature displayed is same as outside temperature, inspect component and ECM connections. Problem is intermittent.
2. If temperature displayed is 284°F (140°C) or more, go to step 5). If temperature displayed is -40°F (-40°C), turn ignition off. Disconnect IAT sensor connector. Connect a jumper wire between IAT sensor wiring harness connector terminals. Turn ignition on. Monitor IAT sensor temperature on scan tester.
3. If temperature displayed is 284°F (140°C) or more, replace IAT sensor and retest. If temperature displayed is less than 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM behind bottom center of instrument panel, in front of console. Connect a jumper wire between terminals No. 3 (Yellow/Black wire) and No. 9 (Brown wire) at ECM E6 connector. see scheme 3
4. If temperature displayed on scan tester is 284°F (140°C) or more, check for an open in wiring harness between IAT sensor connector and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If temperature displayed on scan tester is less than 284°F (140°C), replace ECM and retest.
5. Turn ignition off. Disconnect IAT sensor connector. Turn ignition on. If temperature displayed on scan tester is -40°F (-40°C), replace IAT sensor and retest. If temperature displayed is not -40°F (-40°C), turn ignition off.
6. Access ECM behind bottom center of instrument panel, in front of console. Disconnect ECM E6 connector. see scheme 3 Turn ignition on. If temperature displayed is -40°F (-40°C), inspect and repair wiring harness between IAT sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If temperature displayed by scan tester is not -40°F (-40°C), replace ECM and retest.

1. Connect scan tester to DLC3 connector. (Scheme 10) Turn ignition on. Turn on scan tester. Monitor ECT sensor temperature. If temperature displayed is same as actual coolant temperature, inspect component and ECM connections. Problem is intermittent.
2. If temperature displayed is 284°F (140°C) or more, go to step 5). If temperature displayed is -40°F (-40°C), turn ignition off. Disconnect ECT sensor connector. Connect a jumper wire between ECT sensor wiring harness connector terminals. Turn ignition on. Using scan tester, monitor ECT sensor temperature.
3. If temperature displayed is 284°F (140°C) or more, replace ECT sensor and retest. If temperature displayed is less than 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM behind bottom center of instrument panel, in front of console. Connect a jumper wire between terminals No. 4 (White wire) and No. 9 (Brown wire) at ECM E6 connector. see scheme 3
4. If temperature displayed on scan tester is 284°F (140°C) or more, inspect and repair circuits for open between ECT sensor wiring harness connector and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If temperature displayed on scan tester is less than 284°F (140°C), replace ECM and retest.
5. Turn ignition off. Disconnect ECT sensor connector. Turn ignition on. If temperature displayed on scan tester is -40°F (-40°C), replace ECT sensor and retest. If temperature displayed is not -40°F (-40°C), turn ignition off.
6. Access ECM behind bottom center of instrument panel, in front of console. Disconnect ECM E6 connector. see scheme 3 Turn ignition on. If temperature displayed is -40°F (-40°C), inspect and repair circuits between ECT sensor and ECM for short. See appropriate wiring diagram in WIRING DIAGRAMS article. If temperature displayed by scan tester is not -40°F (-40°C), replace ECM and retest.

Circuit Description

The ECT sensor is a thermistor sensor that monitors engine coolant temperature. DTC is set when ECT sensor temperature value is 95°F (35°C) or less for at least 20 minutes of engine operation. Possible causes are

1. Engine Coolant Temperature (ECT) sensor.
2. Cooling system.

Note. If DTCs P0115 and P0116 are output together, an open may exist in ECT sensor circuit. Perform DTC P0115 circuit test before performing DTC P0116 circuit test.

If only DTC P0116 is displayed, replace ECT sensor and retest. If other codes are displayed, diagnose and repair those codes first and retest.

1. Connect scan tester to DLC3 connector. (Scheme 10) Turn ignition on. Turn on scan tester. Monitor throttle valve opening percentage. Opening percentage should be approximately 10 percent with fully closed throttle.
2. Depress accelerator pedal to floor (WOT). Opening percentage should be approximately 70 percent. If percentages are as specified, inspect all connections. Problem may be intermittent.
3. If percentages are not as specified, turn ignition off. Disconnect TP sensor connector. Turn ignition on. Using DVOM, measure voltage between ground and terminal No. 4 (Yellow wire) at TP sensor wiring 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 7).
4. Check TP sensor. See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article. Replace sensor as necessary. If sensor is okay, go to next step.
5. Access ECM behind bottom center of instrument panel, in front of console. Turn ignition on. Backprobing ECM connector, measure voltage between terminals No. 9 (Brown wire) and No. 11 (Light Green wire) at ECM E6 connector. see scheme 3 Voltage should be.3-.8 volt with throttle fully closed, and 3.2-4.9 volts with throttle fully open (WOT).
6. If voltage is as specified, replace ECM and retest. If voltage is not as specified, check for an open or short in wiring harness between TP sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
7. Access ECM behind bottom center of instrument panel, in front of console. Turn ignition on. Backprobing ECM connector, measure voltage between terminals No. 1 (Red wire) and No. 9 (Brown wire) at ECM E6 connector. see scheme 3 If voltage is 4.5-5.5 volts, check wiring harness for an open in Red wire. If voltage is not 4.5-5.5 volts, replace ECM and retest.

If only DTC P0121 is displayed, replace TP sensor and retest. If other codes are displayed, diagnose and repair those codes first and retest.

1. Connect scan tester to DLC3 connector. (Scheme 10) Start vehicle and warm engine to normal operating temperature. Turn on scan tester. Monitor sensor No. 1. Snap accelerate engine 3 times. Sensors should indicate a rich signal (.45 volt or more) at least once.
2. If a rich signal is indicated at least once, replace ECM and retest. If sensor does not display a rich signal at least once, inspect circuits between ECM and sensor for an open or short circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If circuits are okay, replace oxygen sensor and retest.

Test Drive Confirmation

1. If using OBD-II scan tester, go to next step. If using Toyota scan tester, connect scan tester. (Scheme 10) Switch scan tester to CHECK mode. Start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 1-3 minutes. Stop vehicle and allow to idle for one minute. If malfunction exists, MIL will illuminate.
2. If using OBD-II scan tester, start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 1-3 minutes. Stop vehicle and allow to idle for one minute. Turn vehicle off. Repeat driving and idle part of test. If malfunction exists, MIL will illuminate.

Diagnosis & Repair Procedure

1. Inspect circuits between ECM and oxygen sensor for opens or shorts. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If all circuits are okay, connect scan tester. (Scheme 10)
2. Start engine and warm to normal operating temperature. Monitor oxygen sensor output voltage and short-term fuel trim. If scan tester indicates a lean condition (.55 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), see DTC P0171 - SYSTEM TOO LEAN (FUEL TRIM), DTC P0172 SYSTEM TOO RICH (FUEL TRIM) circuit test.
3. If scan tester indicates other than reading in step 2), operate engine at 2500 RPM for 90 seconds. Monitor oxygen sensor voltage. If voltage constantly fluctuates in wide range (.3-.9 volt), perform TEST DRIVE CONFIRMATION. If voltage does not fluctuate, or stays in narrow range, replace sensor and retest.

If only DTC P0133 is displayed, replace oxygen sensor and retest. If other codes are displayed, diagnose and repair those codes first and retest.

1. If any other codes are displayed other than DTC P0136, diagnose and repair those codes first. If only DTC P0136 is displayed, inspect circuits between ECM and sensor for opens or shorts. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
2. If all circuits are okay, connect scan tester. (Scheme 10) Start and warm engine to normal operating temperature. Monitor sensor No. 2 output voltage. Snap accelerate engine 3 times. Voltage should fluctuate from.4-.5 volt or more.
3. If voltage responds correctly, inspect sensor wiring harness connector. Problem may be intermittent. If voltage does not respond correctly, replace sensor and retest.

1. Access ECM behind bottom center of instrument panel, in front of console. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between ground and terminal No. 19 (Blue/Black wire) at ECM E5 connector. see scheme 3
2. If voltage is 9-14 volts, replace ECM and retest. If voltage is not 9-14 volts, turn ignition off. Disconnect oxygen sensor connector. Using ohmmeter, measure resistance between terminals No. 1 (Blue/Black wire) and No. 2 (Black/Red wire) at oxygen sensor connector.
3. If resistance is 11-16 ohms at 68°F (20°C), inspect circuits between ECM and sensor. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If resistance is not 11-16 ohms, replace sensor and retest.

1. Inspect all air induction components. Repair as necessary. If air induction components are okay, connect scan tool. (Scheme 10) Start engine and warm to normal operating temperature. Monitor heated oxygen sensor output voltage and short-term fuel trim.
2. If scan tester indicates a lean condition (.55 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), go to next step. If results are other than shown, see DTC P0130 - OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test.
3. Inspect fuel pressure. See «BASIC TESTING»(ref-21925) article. Repair as necessary. If fuel pressure is okay, inspect fuel injectors. See SYSTEM/COMPONENT TESTS article. Replace injectors as necessary.
4. If all injectors are okay, inspect Manifold Absolute Pressure (MAP) sensor and Engine Coolant Temperature (ECT) sensor. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If both components are okay, inspect ignition system. See IGNITION CHECKS in «BASIC TESTING»(ref-21925) article. Repair as necessary. If ignition system is okay, replace ECM and retest.

A misfire is determined by the ECM. The ECM uses signals provided by the crankshaft and camshaft position sensors. If the engine speed rate has changed enough to equal a preset number, a misfire is detected and the MIL is illuminated. If the misfire rate is high enough, and driving conditions will cause catalytic converter damage or overheating, the MIL blinks when a misfire is occurring.

DTC is set when misfiring of random cylinders is detected during any particular 200 or 1000 revolutions. Possible causes are

1. Ignition system.
2. Injector(s).
3. Fuel pressure.
4. EGR system.
5. Engine compression.
6. Valve clearance.
7. Valve timing.
8. Manifold Absolute Pressure (MAP) sensor.
9. Engine Coolant Temperature (ECT) sensor.

1. Inspect spark plug and check for spark at misfiring cylinder. See «BASIC TESTING»(ref-21925) article. Repair as necessary. If spark plug is okay and spark is present, go to next step.
2. Access ECM behind bottom center of instrument panel, in front of console. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between ground and injector terminals at ECM E5 connector. See «IDENTIFYING INJECTOR TERMINALS»(ref-21945-S10008346812001010300000) table. see scheme 3 If voltage is 9-14 volts for each circuit, go to step 4). If voltage is not 9-14 volts, go to next step. IDENTIFYING INJECTOR TERMINALS Injector No. (1) Terminal No. Wire Color 1 12 Yellow 2 25 Black/White 3 24 Black 4 4 Black/Red (1) Terminals are located in ECM E5 connector.
3. Disconnect injector of misfiring cylinder. Using ohmmeter, measure resistance between injector terminals. If resistance is 13.4-14.2 ohms at 68°F (20°C), inspect circuits between ECM and injector for open or short. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If resistance is not 13.4-14.2 ohms, replace injector.
4. Check fuel pressure. See «BASIC TESTING»(ref-21925) article. Repair as necessary. If fuel pressure is okay, inspect fuel injector performance. See SYSTEM/COMPONENT TESTS article. Replace as necessary.
5. If all injectors are okay, inspect EGR system. See SYSTEM/COMPONENT TESTS article. Repair as necessary. If EGR system is okay, inspect MAP sensor and ECT sensor. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If both components are okay, also inspect engine compression, valve clearance and valve timing. See «BASIC TESTING»(ref-21925) article.

See DTC P0300 - RANDOM MISFIRE DETECTED circuit test.

See DTC P0300 - RANDOM MISFIRE DETECTED circuit test.

1. Disconnect CKP sensor connector. Using ohmmeter, measure resistance between sensor connector terminals. Resistance should be 1630-2740 ohms (cold sensor) or 2065-3225 ohms (hot sensor).
2. If resistance is not as specified, replace sensor. If resistance is as specified, inspect circuits between ECM and CKP sensor for open or short. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If both circuits are okay, remove and inspect sensor. Also inspect signal plate. Replace as necessary. If both components are okay, replace ECM and retest.

1. Disconnect CMP sensor connector. Measure resistance between terminals G+ and G- at sensor connector. (Scheme 11) Resistance should be 185-275 ohms (cold sensor) or 240-325 ohms (hot sensor).
2. If resistance is not as specified, replace sensor. If resistance is as specified, inspect circuits between ECM and CMP sensor for open or short. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
3. If both circuits are okay, inspect sensor installation. Repair as necessary. If installation is okay, replace ECM and retest.

Scheme 11

1. Connect scan tester. (Scheme 10) Start and warm engine to normal operating temperature. Operate vehicle at 43-56 MPH for 3 minutes or more. Stop vehicle and allow to idle for about 2 minutes. Turn ignition off.
2. Start engine and allow to idle. Operate vehicle at 43-56 MPH for 3 minutes or more. Stop vehicle and allow to idle for about 2 minutes.
3. Using scan tester, check READINESS TESTS. If COMPL is displayed on scan tester and MIL is not illuminated, system is normal. If INCMPL is displayed and MIL is not illuminated, repeat test drive procedure.

Diagnosis & Repair (Using Toyota Scan Tester)

1. Inspect vacuum hoses. See appropriate illustration in VACUUM DIAGRAMS article. Repair as necessary. If all hoses are okay, inspect VSV. Using scan tester, select ACTIVE TEST mode. Check operation of VSV when activated by scan tester. VSV is mounted on top right rear of engine.
2. Start and run engine. With EGR system off, air from port "E" should exhaust from small filter on end of valve. (Scheme 12) With EGR system on, air from port "E" should exhaust from port "F". If valve operates as specified, go to step 6). If valve does not operate as specified, go to next step.
3. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 37-44 ohms at 68°F (20°C). Check for continuity between each terminal and body of valve. If continuity exists, replace VSV. If continuity does not exist, go to next step.
4. Check VSV operation. Apply battery voltage to VSV terminals. Air should from port "E" should exhaust from port "F". (Scheme 12) Remove battery voltage from valve terminals. Air from port "E" should exhaust from small filter on end of valve. Replace VSV as necessary. If VSV operates as specified, go to next step.
5. Check for and open or short circuit in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
6. Inspect EGR vacuum modulator. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If modulator is okay, inspect EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If components are okay, go to next step.
7. Check Manifold Absolute Pressure (MAP) sensor. See SYSTEM/COMPONENT TESTS article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.

Scheme 12

Diagnosis & Repair (Using OBD-II Scan Tester)

1. Inspect all EGR system vacuum hoses. Replace as necessary. Access ECM behind bottom center of instrument panel, in front of console. Ensure ignition is off. Disconnect ECM E5 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 23 (Black/White wire) at ECM E5 connector.
2. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Air from port "E" should exhaust from port "F". (Scheme 12) Disconnect jumper wire. Air from port "E" should exhaust from small filter on end of valve. If valve operates as specified, go to step 6). If valve does not operate as specified, go to next step.
3. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 37-44 ohms at 68°F (20°C). Check for continuity between each terminal and body of valve. If continuity exists, replace VSV. If continuity does not exist, go to next step.
4. Check VSV operation. Apply battery voltage to valve terminals. Air from port "E" should exhaust from port "F". (Scheme 12) Remove battery voltage from valve terminals. Air from port "E" should exhaust from small filter on end of valve. Replace VSV as necessary.
5. Check for an open or short in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
6. Inspect EGR vacuum modulator. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR valve is okay, go to next step.
7. Check Manifold Absolute Pressure (MAP) sensor. See SYSTEM/COMPONENT TESTS article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.

1. Connect scan tester. (Scheme 10) Start and warm engine to normal operating temperature. Operate vehicle at 43-56 MPH for 3 minutes or more. Stop vehicle and allow to idle for about 2 minutes. Turn ignition off.
2. Start engine and allow to idle. Operate vehicle at 43-56 MPH for 3 minutes or more. Stop vehicle and allow to idle for about 2 minutes.
3. Check READINESS TESTS. If COMPL is displayed on scan tester and MIL is not illuminated, system is normal. If INCMPL is displayed and MIL is not illuminated, repeat test drive procedure.

1. Inspect all EGR system vacuum hoses. Replace as necessary. If vacuum hoses are okay, check EGR valve. See SYSTEM/COMPONENT TESTS article. Replace EGR valve as necessary. If EGR valve is okay, go to next step.
2. Access ECM behind bottom center of instrument panel, in front of console. Ensure ignition is off. Disconnect ECM E5 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 23 (Black/White wire) at ECM E5 connector.
3. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Air from port "E" should exhaust from port "F". (Scheme 12) Disconnect jumper wire. Air from port "E" should exhaust from small filter on end of valve. If valve operates as specified, go to step 7). If valve does operate as specified, go to next step.
4. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 37-44 ohms at 68°F (20°C). Check for continuity between each terminal and body of valve. If continuity exists, replace VSV. If continuity does not exist, go to next step.
5. Check VSV operation. Apply battery voltage to valve terminals. Air from port "E" should exhaust from port "F". (Scheme 12) Remove battery voltage from valve terminals. Air from port "E" should exhaust from small filter on end of valve. Replace VSV as necessary.
6. Check for an open or short in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
7. Inspect EGR vacuum modulator. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR valve is okay, go to next step.
8. Check Manifold Absolute Pressure (MAP) sensor. See SYSTEM/COMPONENT TESTS article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.

The ECM compares waveform of oxygen sensor located before catalytic converter with waveform of oxygen sensor located after converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when both oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are

1. Catalytic converter.
2. Oxygen sensor open or short circuit.
3. Oxygen sensor.

Note. Oxygen sensor located in front of catalytic converter is referred to as sensor No. 1. Oxygen sensor located behind catalytic converter is referred to as sensor No. 2.

1. Connect scan tester. (Scheme 10) Start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 5-10 minutes. Stop vehicle. Retrieve codes. See «SELF-DIAGNOSTIC SYSTEM»(ref-21945-S40229862332001010300000).
2. If codes other than P0420 are present, diagnose and repair those codes first. If DTC P0420 is only displayed, inspect oxygen sensor circuits. See DTC P0130 - HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test. Repair as necessary. If oxygen sensor circuits and sensor are okay, replace catalytic converter and retest.

1. Test drive vehicle and check operation of speedometer. If speedometer is not functioning correctly, see appropriate INSTRUMENT PANELS article. If speedometer is functioning correctly, go to next step.
2. Disconnect cruise control ECU 26-pin connector. ECU is located behind bottom center of instrument panel, in front of console. Ensure ignition is off. Shift gear selector to Neutral. Lift and support front of vehicle. Turn ignition on. Using DVOM, measure voltage between ground and terminal No. 9 (Violet/White wire) at ECM E7 connector, while rotating front wheels. see scheme 3
3. As front wheels are rotated, voltage should pulse between zero and 5-6 volts. If voltage is as specified, replace ECM and retest. If voltage is not as specified, inspect Violet/White wire between instrument cluster and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.

Repair & Diagnosis

1. Inspect air induction system for leaks. Repair as necessary. If air induction system is okay, go to next step.
2. Ensure ignition is off. Access ECM behind bottom center of instrument panel, in front of console. Disconnect ECM E5 connector. Turn ignition on. Using DVOM, measure voltage between ground and terminals No. 9 (Black/White wire) and No. 10 (Black/Blue wire) at ECM E5 connector. see scheme 3 If both readings are 9-14 volts, go to step 4). If any reading is not 9-14 volts, go to next step.
3. Turn ignition off. Disconnect IAC valve connector. IAC valve is located in front of throttle body at 6 o'clock position. Using ohmmeter, measure resistance between terminal No. 2 and terminals No. 1 and 3 at IAC valve. (Scheme 13) If resistance is not 17-25 ohms (cold) and 22-29 ohms (hot), replace IAC valve. If resistance is 17-25 ohms (cold) and 22-29 ohms (hot), check for an open or short in wiring harness between IAC valve and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
4. Inspect IAC valve operation. See SYSTEM/COMPONENT TESTS article. Replace IAC valve as necessary. If valve is okay, replace ECM and retest.

Scheme 13

1. Check for spark at misfiring cylinder. See IGNITION CHECKS in «BASIC TESTING»(ref-21925) article. If spark is present, go to next step. If spark is not present, go to step 4).
2. Check for open or short in IGF circuit (Blue/Yellow wire) between ECM and igniter. Igniter is located in left side of engine compartment. See appropriate wiring diagram in WIRING DIAGRAMS. Repair as necessary. If circuit is okay, go to next step.
3. Disconnect Black 5-pin igniter connector. Access ECM behind bottom center of instrument panel, in front of console. Turn ignition on. Measure voltage between ground and terminal No. 3 (Blue/Yellow wire) at ECM E5 connector. see scheme 3 If voltage is 4.5-5.5 volts, replace igniter. If voltage is not 4.5-5.5 volts, replace ECM and retest.
4. Check for open or short in IGT circuit (Yellow/Green wire) between ECM and igniter. See appropriate wiring diagram in WIRING DIAGRAMS. Repair as necessary. If circuit is okay, go to next step.
5. Access ECM behind bottom center of instrument panel, in front of console. Backprobing ECM connector, measure voltage between ground and terminal No. 20 (Yellow/Green wire) at ECM E5 connector while cranking engine. see scheme 3 If voltage is.1-4.5 volts, go to next step. If voltage is not.1-4.5 volts, replace ECM and retest.
6. Disconnect Black 5-pin igniter connector. Backprobing ECM connector, measure voltage between ground and terminal No. 20 (Yellow/Green wire) at ECM E5 connector while cranking engine. If voltage is.1-4.5 volts, go to next step. If voltage is not.1-4.5 volts, replace ECM and retest.
7. Turn ignition on. Measure voltage between ground and terminal No. 3 (Black wire) at igniter wiring harness connector. (Scheme 14) If voltage is 9-14 volts, go to next step. If voltage is not 9- 14 volts, check and repair igniter power source circuit. See appropriate wiring diagram in WIRING DIAGRAMS article.
8. Check for an open or short in wiring harness between ignition switch and ignition coil, and between ignition coil and igniter. Repair as necessary. If wiring is okay, check ignition coil. See IGNITION CHECKS in «BASIC TESTING»(ref-21925) article. Replace coil as necessary. If coil is okay, replace igniter.

Scheme 14

1. Connect Toyota scan tester. (Scheme 10) Turn ignition and scan tester on. Using scan tester, read STA signal. Turn ignition switch to START position and release.
2. STA signal should be OFF with ignition switch in ON position. STA signal should be ON with ignition switch in START position. If STA signal is not as specified, go to next step. If STA signal is as specified, inspect all applicable connectors. See appropriate wiring diagram in WIRING DIAGRAMS article. Malfunction may be intermittent.
3. Check for an open in wiring harness between starter relay and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If circuit is okay, replace ECM and retest.

1. Turn ignition off. Access ECM behind bottom center of instrument panel, in front of console. Using DVOM, measure voltage between ground and terminal No. 1 (Red/White wire) at ECM E7 connector. see scheme 3 If voltage is 9-14 volts, replace ECM and retest. If voltage is not 9-14 volts, go to next step.
2. Remove and inspect EFI fuse. EFI fuse is located in engine compartment fuse box. Replace as necessary. If fuse is okay, inspect circuit between EFI fuse and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.

1. Disconnect PNP switch connector. PNP switch is located at transmission where shifter select cable is mounted. Using ohmmeter, check continuity of switch terminals in specified positions. (Scheme 15) Replace switch as necessary.
2. If switch is okay, access ECM behind glove box. Turn ignition on. Using DVOM, measure voltage between ground and terminal No. 22 (Black/White wire) at ECM E7 connector. see scheme 3
3. Voltage should be zero volts in "P" or "N" position. Voltage should be 9-14 volts in any other shift selector position. If all voltages measured are as specified, replace ECM and retest.
4. If any voltage is not as specified, check for an open or short in wiring harness between PNP switch and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.

Scheme 15

Scheme 16