Engine Control System Tests W/codes - 3.4L: Diagnosis Toyota Tacoma I

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 - 3.4L»(ref-22483) article. See «ECM LOCATION»(ref-22484-S40448941792001010300000) .
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»(ref-22484-S18247938402001010300000) .

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 tool. Retrieve codes and record any freeze-frame data (if applicable). See «RETRIEVING DIAGNOSTIC TROUBLE CODES»(ref-22484-S18247938402001010300000) .
3. Clear Trouble Codes Clear codes. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-22484-S04100019212001010300000) .
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. See «CIRCUIT TESTS»(ref-22484-S15424360472001010300000) . If no codes are present, proceed to «TESTS W/O CODES - 3.4L»(ref-22487) 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-22484-S04100019212001010300000) . 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 tool or On-Board Diagnostic (OBD-II) scan tool that complies with SAE standard J-1978. Toyota scan tool or OBD-II scan tool may be operated in NORMAL mode when retrieving trouble codes. Only Toyota scan tool 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 tool, when ignition switch is turned from ON to ACC or OFF position or scan tool 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 have been recorded.

CHECK Mode Code Retrieval (Toyota Scan Tool Only)

1. Ensure vehicle battery is fully charged. Apply parking brake. Shift transmission/transaxle into Neutral (M/T) or Park (A/T). Turn A/C and all accessories off. Ensure throttle is in idle position.
2. Turn ignition off. Connect scan tool to Data Link Connector (DLC) No. 3. See «DATA LINK CONNECTOR»(ref-22484-S15902827412001010300000) under INTRODUCTION. Turn ignition on with engine off. Turn scan tool on.
3. Switch scan tool from NORMAL mode to CHECK mode. CHECK mode is operational if MIL on instrument cluster flashes. Start engine. Ensure MIL goes off. Try to simulate conditions of driveability complaint described by customer. NOTE: If ignition switch is turned from ON to ACC or OFF position, all DTCs and freeze-frame data will be erased. DO NOT switch modes until all DTCs and freeze-frame data are recorded.
4. Record any DTCs and freeze-frame data displayed for system diagnosis. If driveability problem exists and no codes are present, go to «TESTS W/O CODES - 3.4L»(ref-22487) article for diagnosis by symptom.
5. If any DTCs are present, perform appropriate circuit test. See «DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION»(ref-22484-S01616854302001010300000) table. For more information on freeze-frame data, see «FREEZE-FRAME DATA»(ref-22484-S04921997392001010300000) under INTRODUCTION. For information on 2-trip detection logic codes, see «TWO-TRIP DETECTION LOGIC»(ref-22484-S42550761882001010300000) under INTRODUCTION.
6. After repairs for DTC have been completed, DTC must be cleared from ECM memory. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-22484-S04100019212001010300000) .

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 tool and scan tool manufacturer's instructions. NOTE: If using Toyota scan tool, 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.

DIAGNOSTIC TROUBLE CODE (DTC) 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»(ref-22484-S15424360472001010300000) .

DLC NO. 3 INSPECTION

1. If scan tool displays UNABLE TO CONNECT TO VEHICLE when scan tool is connected, try scan tool on another vehicle. If scan tool operates on another vehicle, go to next step. If scan tool does not operate on another vehicle, problem is probably with scan tool.
2. Check DLC No. 3 for loose or damaged terminals. Ensure DLC No. 3 terminals are in correct position in connector. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) 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 DLC No. 3. See «DLC NO»(ref-22484-S11344007652001010300000). 3 VOLTAGE & RESISTANCE SPECIFICATIONS table. (Scheme 120) If voltage and resistance readings are not as specified, check wiring circuit. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article.

DLC NO. 3 VOLTAGE & RESISTANCE SPECIFICATIONS

Scheme 120

Diagnosis & Repair

1. Connect scan tool to DLC No. 3 connector. (Scheme 121) Start vehicle engine and allow to idle. Using scan tool, monitor MAF flow rate. If scan tool reading is 0.0 gm/sec., go to next step. If reading is 11-25 gm/sec. once engine is at normal operating temperature, go to step 5).
2. Disconnect MAF sensor Black 5-pin connector. Ensure ignition is on. Using DVOM, measure voltage between ground and terminal No. 1 (White/Red wire) at MAF sensor wiring harness connector. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, check for open circuit in wiring harness between EFI main relay and MAF sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
3. Access ECM behind glove box. Start engine. Backprobe ECM connector. On A/T models, measure voltage between ground and terminal No. 8 (Gray/Red wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between ground and terminal No. 2 (Gray/Red wire) at ECM E7 connector. On all models, if voltage is 1.1-1.5 volts, replace ECM and retest.
4. If voltage is not 1.1-1.5 volts, check for open or short circuit in wiring harness between MAF sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace MAF sensor and retest.
5. Access ECM behind glove box. Turn ignition off. Using ohmmeter, backprobe ECM connector. On A/T, check continuity between ground and terminal No. 18 (Brown/White wire) at ECM E7 connector. On M/T models, check continuity between ground and terminal No. 8 (Brown/White wire) at ECM E7 connector. (Scheme 121)or (Scheme 122).
6. On all models, if continuity does not exist, replace ECM and retest. If continuity exists, check for open circuit in wiring harness between MAF sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace MAF sensor.

Scheme 121

Scheme 122

Diagnosis & Repair Procedure

If only DTC P0101 is displayed, replace MAF sensor and retest. If other codes are displayed, diagnose and repair those codes first and retest.

1. Connect scan tool to DLC No. 3 connector. (Scheme 121) Turn ignition on. Using scan tool, monitor IAT sensor temperature. If temperature displayed is same as outside temperature, check 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 MAF sensor connector. Connect a jumper wire between terminals No. 3 (Yellow/Green wire) and No. 4 (Brown/Black wire) at MAF sensor wiring harness connector. Turn ignition on. Using scan tool, monitor IAT sensor temperature.
3. If temperature displayed is 284°F (140°C) or more, replace MAF sensor and retest. If temperature displayed is less than 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM behind glove box. On A/T models, connect a jumper wire between terminals No. 22 (Brown/Black wire) and No. 14 (Yellow/Green wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, connect a jumper wire between terminals No. 9 (Brown/Black wire) and No. 12 (Yellow/Green wire) at ECM E7 connector.
4. On all models, if temperature displayed on scan tool is 284°F (140°C) or more, check and repair circuits between MAF sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. If temperature displayed on scan tool is less than 284°F (140°C), replace ECM and retest.
5. Turn ignition off. Disconnect MAF sensor connector. Turn ignition on. If temperature displayed on scan tool is -40°F (-40°C), replace MAF sensor and retest. If temperature displayed is not -40°F (-40°C), turn ignition off.
6. Access ECM behind glove box. Disconnect ECM E7 connector. (Scheme 121)or (Scheme 122). Turn ignition on. If temperature displayed is -40°F (-40°C), check for short circuit in wiring harness between MAF sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. If temperature displayed by scan tool is not -40°F (-40°C), replace ECM and retest.

1. Connect scan tool to DLC No. 3 connector. (Scheme 121) Turn ignition on. Using scan tool, monitor ECT sensor temperature. If temperature displayed is same as actual coolant temperature, check 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. ECT is located near thermostat housing. Connect a jumper wire between ECT sensor wiring harness connector terminals. Turn ignition on. Using scan tool, 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 glove box. On A/T models, connect a jumper wire between terminals No. 20 (Green/Red wire) and No. 22 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, connect a jumper wire between terminals No. 4 (Green/Red wire) and No. 9 (Brown/Black wire) at ECM E7 connector.
4. On all models, if temperature displayed on scan tool is 284°F (140°C) or more, locate and repair open circuit in wiring harness between ECT sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. If temperature displayed on scan tool 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 tool 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 glove box. Disconnect ECM E7 connector. (Scheme 121)or (Scheme 122). Turn ignition on. If temperature displayed is -40°F (-40°C), locate and repair short circuit in wiring harness between ECT sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. If temperature displayed by scan tool is not -40°F (-40°C), replace ECM and retest.

If any other codes are displayed, diagnose and repair those codes first and retest. If only DTC P0116 is displayed, remove and inspect cooling system thermostat. Replace thermostat as necessary and retest. If thermostat is okay, replace ECT sensor and retest.

1. Connect scan tool to DLC No. 3 connector. (Scheme 121) Turn ignition on. Using scan tool, 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 75 percent. If percentages are as specified, check 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. 2 (Green/Black 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 Throttle Position (TP) sensor. See ENGINE SENSORS & SWITCHES in «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace sensor as necessary. If sensor is okay, go to next step.
5. Access ECM behind glove box. Turn ignition on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 22 (Brown/Black wire) and No. 7 (Yellow wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between terminals No. 9 (Brown/Black wire) and No. 10 (Yellow wire) at ECM E7 connector. On all models, voltage should be.3-1.0 volt with throttle fully closed, and 2.7-5.2 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 Yellow wire. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
7. Access ECM behind glove box. Turn ignition on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 22 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, if voltage is 4.5-5.5 volts, check wiring harness for an open in Green/Black 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 tool to DLC No. 3 connector. (Scheme 121) Start vehicle and warm engine to normal operating temperature. Using scan tool, monitor output voltage of sensor No. 1. Snap accelerate engine 3 times. Sensor 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, check for open or short circuit in wiring harness between ECM and oxygen sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace oxygen sensor and retest.

Test Drive Confirmation

1. If using OBD-II scan tool, go to next step. If using Toyota scan tool, connect scan tool. (Scheme 121) Switch scan tool 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 tool, 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.

1. Check for open or short circuit in wiring harness between ECM and oxygen sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, connect scan tool. (Scheme 121)
2. Start engine and warm to normal operating temperature. Using scan tool, monitor heated oxygen sensor output voltage and short-term fuel trim. If scan tool indicates a lean condition (.6 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), see «DTC P0171»(ref-22484-S05979815332001010300000) SYSTEM TOO LEAN (FUEL TRIM), DTC P0172: SYSTEM TOO RICH (FUEL TRIM) circuit test.
3. If scan tool indicates other than reading in step 2), operate engine at 2500 RPM for 90 seconds. Monitor oxygen sensor voltage. If voltage constantly fluctuates from less than.4 volt to more than.6 volt, perform TEST DRIVE CONFIRMATION. If voltage does not fluctuate as specified, 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. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector. If DTC P0135 is set, measure voltage between the following. On A/T models, measure between ground and terminal No. 16 (Pink/Green wire) at ECM E8 connector. On M/T models, measure between ground and terminal No. 3 (Pink/Green wire) at ECM E6 connector.
2. If DTC P0141 is set, measure voltage between the following. On A/T models, measure voltage between ground and terminal No. 15 (Red/White wire) at ECM E8 connector. On M/T models, measure voltage between ground and terminal No. 9 (Red/Green wire) at ECM E6 connector. (Scheme 121)or (Scheme 122). On all models, voltage for each circuit should be 9-14 volts.
3. If voltage is as specified, replace ECM and retest. If voltage is not as specified, turn ignition off. Disconnect appropriate oxygen sensor connector. Using ohmmeter, measure resistance between terminals No. 1 and 2 at oxygen sensor connector. See «IDENTIFYING OXYGEN SENSOR HEATER TERMINALS»(ref-22484-S36423438132001010300000) table. IDENTIFYING OXYGEN SENSOR HEATER TERMINALS Application Terminal No. 1 Terminal No. 2 Sensor No. 1 Pink/Green Wire White/Red Wire Sensor No. 2 A/T Red/White Wire White/Red Wire M/T Red/Green Wire White/Red Wire
4. If resistance is 11-16 ohms at 68°F (20°C), check circuits between ECM and sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If resistance is not as specified, replace sensor and retest.

1. If any codes are displayed other than DTC P0136, diagnose and repair those codes first. If only DTC P0136 is displayed, check for open or short circuit in wiring harness between ECM and oxygen sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
2. If wiring harness is okay, connect scan tool. (Scheme 121) Start and warm engine to normal operating temperature. Monitor output voltage of sensor No. 2. Snap accelerate engine 3 times. Voltage should fluctuate from less than.4 volt to more than.6 volt.
3. If voltage fluctuates as specified, check sensor wiring harness connector. Problem may be intermittent. If voltage does not fluctuate as specified, replace sensor and retest.

1. Check all air induction components. Repair as necessary. If air induction components are okay, connect scan tool. (Scheme 121) Start engine and warm to normal operating temperature. Monitor heated oxygen sensor No. 1 output voltage and short-term fuel trim.
2. If scan tool indicates a lean condition (.6 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»(ref-22484-S03449757142001010300000) HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test.
3. Check fuel pressure. See «BASIC TESTING - 3.4L»(ref-22485) article. Repair fuel pressure as necessary. If fuel pressure is okay, check fuel injectors. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace injectors as necessary.
4. If all injectors are okay, check Mass Airflow (MAF) sensor and Engine Coolant Temperature (ECT) sensor. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace MAF and/or ECT sensor as necessary. If both components are okay, check ignition system. See IGNITION CHECKS in «BASIC TESTING - 3.4L»(ref-22485) article. Repair ignition system as necessary. If ignition system is okay, replace ECM and retest.

Circuit Description

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. Mass Airflow (MAF) sensor.
9. Engine Coolant Temperature (ECT) sensor.

1. Inspect spark plug and check for spark at misfiring cylinder. See «BASIC TESTING - 3.4L»(ref-22485) article. Repair as necessary. If spark plug is okay and spark is present, go to next step.
2. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between ground and injector terminals at ECM E8 connector. See «IDENTIFYING INJECTOR TERMINALS»(ref-22484-S05141817902001010300000) table. (Scheme 121)or (Scheme 122). 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 A/T Models 1 10 White/Red 2 9 White 3 8 White/Green 4 7 Yellow/Red 5 6 White/Blue 6 5 Yellow/Black M/T Models 1 12 White/Red 2 11 White 3 25 White/Green 4 10 Yellow/Red 5 9 White/Blue 6 8 Yellow/Black (1) Terminals are located in ECM E8 connector.
3. Disconnect injector of misfiring cylinder. Using ohmmeter, measure resistance between injector terminals. If resistance is about 13.8 ohms, check for open or short circuit in wiring harness between ECM and injector. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If resistance is not about 13.8 ohms, replace injector.
4. Check fuel pressure. See «BASIC TESTING - 3.4L»(ref-22485) article. Repair fuel pressure as necessary. If fuel pressure is okay, check fuel injector performance. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace fuel injectors as necessary.
5. If all injectors are okay, check EGR system. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Repair EGR system as necessary. If EGR system is okay, check MAF sensor and ECT sensor. See SYSTEM/COMPONENT TESTS - 3.4L article. Replace MAF and/or ECT sensor as necessary. If both components are okay, also check engine compression, valve clearance and valve timing. See «BASIC TESTING - 3.4L»(ref-22485) article.

Note. 4WD models with an extended cab and V6 engine is not equipped with EGR system.

See DTC P0300 RANDOM MISFIRE DETECTED circuit test.

1. Connect scan tool. (Scheme 121) Disconnect ED1 connector. ED1 connector is a wire-to-wire connector located near front of right cylinder head. ED1 connector is a 3-pin Dark Gray connector.
2. Remove, switch and install terminals No. 1 and 2 from male connector. (Scheme 123) Connect ED1 connector. Turn ignition on. Clear trouble codes. See «SELF-DIAGNOSTIC SYSTEM»(ref-22484-S13808868582001010300000). Start and warm engine to normal operating temperature.
3. Snap accelerate engine 3 times. Retrieve trouble codes. See «SELF-DIAGNOSTIC SYSTEM»(ref-22484-S13808868582001010300000). If same code(s) are repeated as before, go to next step. If code(s) have changed, go to step 5).
4. Check for open or short circuit in wiring harness between ED1 connector and ECM. Repair wiring as necessary. If wiring harness is okay, replace ECM and retest. Ensure ED1 male connector terminals are returned to their original position.
5. Check for open or short circuit in wiring harness between ED1 connector and knock sensor(s). To access wiring harness, it may be necessary to remove intake manifold. See ENGINE SENSORS in «REMOVE/INSTALL/OVERHAUL - 3.4L»(ref-22488) article. Repair wiring as necessary. If wiring harness is okay, replace knock sensor. Ensure ED1 male connector terminals are returned to their original position.

Scheme 123

1. Disconnect CKP sensor connector. Using ohmmeter, measure resistance between CKP sensor connector terminals. Resistance should be 1630-2740 ohms (cold sensor) or 2065-3225 ohms (hot sensor).
2. Replace CKP sensor as necessary. If CKP sensor is okay, check for open or short circuit in wiring harness between ECM and CKP sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, remove and inspect CKP sensor. Also inspect signal plate. Replace CKP sensor and/or signal plate as necessary. If both components are okay, replace ECM and retest.

1. Disconnect CMP sensor connector. Using ohmmeter, measure resistance between CMP sensor connector terminals. Resistance should be 835-1400 ohms (cold sensor) or 1060-1645 ohms (hot sensor).
2. Replace CMP sensor as necessary. If CMP sensor is okay, check for open or short circuit in wiring harness between ECM and CMP sensor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
3. If wiring harness is okay, remove and inspect CMP sensor. Also inspect signal plate. Replace CMP sensor and/or signal plate as necessary. If both components are okay, replace ECM and retest.

1. Connect scan tool. (Scheme 121) 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 tool, check READINESS TESTS. If COMPL is displayed on scan tool 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 Tool)

1. Connect scan tool. (Scheme 121) Turn ignition on. Using scan tool, read EGR gas temperature. If temperature is 50°F (10°C) or more, go to step 6). If temperature is less than 50°F (10°C), go to next step. NOTE: If EGR gas temperature is 37.6°F (3.1°C), open exists in EGR temperature sensor circuit.
2. Disconnect EGR temperature sensor connector. Sensor is mounted on EGR valve body. Connect a jumper wire between sensor wiring harness connector terminals.
3. If EGR gas temperature displayed is not about 318°F (159°C), go to next step. If EGR gas temperature displayed is about 318°F (159°C), check sensor connectors and terminals. Repair as necessary. If connectors are okay, replace sensor and retest.
4. Remove jumper wire. Turn ignition off. Access ECM behind glove box. On A/T models, connect jumper wire between terminal No. 21 (Pink/Green wire) and No. 22 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, connect a jumper wire between terminals No. 9 (Brown/Black wire) and No. 14 (Pink/Green wire) at ECM E7 connector. On all models, turn ignition on.
5. If EGR temperature displayed is about 318°F (159°C), locate and repair open circuit in wiring harness between ECM and EGR temperature sensor. If temperature displayed is not about 318°F (159°C), replace ECM and retest.
6. Check vacuum hoses. See appropriate illustration in «VACUUM DIAGRAMS - 3.4L»(ref-22486) article. Replace vacuum hoses as necessary. If all hoses are okay, check EGR VSV. Using scan tool, select ACTIVE TEST mode. Check operation of EGR VSV when activated by scan tool. See appropriate illustration in «THEORY/OPERATION - 3.4L»(ref-22482) article for EGR VSV location.
7. Apply air pressure to EGR VSV port "E". (Scheme 124) With EGR system off, air from port "E" should flow from small filter on end of EGR VSV. With EGR system on, air from port "E" should flow from port "G". If EGR VSV operates as specified, go to step 10). If EGR VSV does not operate as specified, go to next step.
8. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each terminal and body of EGR VSV. Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
9. Check EGR VSV operation. Apply air pressure to EGR VSV port "E". Air from port "E" should flow from port "G". (Scheme 124) Apply battery voltage to valve terminals. Air from port "E" should flow from small filter on end of valve. Replace EGR VSV as necessary. If EGR VSV operates as specified, check for open circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
10. Check EGR vacuum modulator. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace EGR vacuum modulator as necessary. If EGR vacuum modulator is okay, check EGR valve. See SYSTEM/COMPONENT TESTS - 3.4L article. Replace EGR valve as necessary. If components are okay, go to next step.
11. Ensure all components are connected. Check EGR temperature sensor. Start and run engine. Using scan tool, select ACTIVE TEST mode (EGR system ON). Run engine at 4000 RPM for 3 minutes. Monitor EGR gas temperature.
12. If temperature is 284°F (140°C) or more, replace ECM and retest. If temperature is less than 284°F (140°C), replace EGR temperature sensor.

Scheme 124

Diagnosis & Repair (Using OBD-II Scan Tool)

1. Disconnect EGR temperature sensor. EGR temperature sensor is mounted on EGR valve body. Using ohmmeter, measure resistance between sensor terminals. If resistance is 600,000 ohms or less, go to next step. If resistance is more than 600,000 ohms, check sensor. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace as necessary.
2. Turn ignition on. Using DVOM, measure voltage between sensor wiring harness connector terminals. If voltage is 4.5-5.5 volts, go to step 4). If voltage is not 4.5-5.5 volts, go to next step.
3. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe connector. On A/T models, measure voltage between terminal No. 21 (Pink/Green wire) and No. 22 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between terminals No. 9 (Brown/Black wire) and No. 14 (Pink/Green wire) at ECM E7 connector. On all models, if voltage is 4.5-5.5 volts, check for open circuit in wiring harness between EGR temperature sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If voltage is not 4.5-5.5 volts, replace ECM and retest.
4. Check all EGR system vacuum hoses. Replace vacuum hoses as necessary. If EGR vacuum hoses are okay, access ECM behind glove box. Ensure ignition is off. Disconnect ECM E6 connector (A/T models) or E8 connector (M/T models). Turn ignition on. On A/T models, connect a jumper wire between ground and terminal No. 8 (Red/White wire) at ECM E6 connector. On M/T models, connect a jumper wire between ground and terminal No. 18 (Red/White wire) at ECM E8 connector.
5. With jumper wire connected, EGR Vacuum Switching Valve (VSV) is on. Apply air pressure to EGR VSV port "E". (Scheme 124) Air from port "E" should flow from small filter on end of EGR VSV. Disconnect jumper wire. Air from port "E" should flow from port "G". If EGR VSV operates as specified, go to step 8). If EGR VSV does not operate as specified, go to next step.
6. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each terminal and body of EGR VSV. Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
7. Check EGR VSV operation. Apply battery voltage to EGR VSV terminals. Apply air pressure to EGR VSV port "E". (Scheme 124) Air from port "E" should flow from small filter on end of EGR VSV. Remove battery voltage from valve terminals. Air from port "E" should flow from port "G". Replace EGR VSV as necessary. If EGR VSV operates as specified, check for open circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
8. Check EGR vacuum modulator. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace EGR vacuum modulator as necessary. If EGR vacuum modulator is okay, check EGR valve. See SYSTEM/COMPONENT TESTS - 3.4L article. Replace EGR valve as necessary. If components are okay, go to next step.
9. Disconnect EGR temperature sensor connector. Start engine. Ensure engine is at normal operating temperature. Disconnect EGR VSV connector. Run engine at 4000 RPM for 3 minutes and measure resistance between EGR temperature sensor terminals. If resistance is 4300 ohms or less, replace ECM and retest. If resistance is more than 4300 ohms, replace EGR temperature sensor.

1. Connect scan tool. (Scheme 121) 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 tool 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 Tool)

1. Connect scan tool. (Scheme 121) Turn ignition on. Read EGR gas temperature. If EGR gas temperature is 302°F (150°C), go to step 4). If EGR gas temperature is not 302°F (150°C), go to next step. NOTE: If EGR gas temperature displayed is 318.7°F (159.3°C), a short exist in EGR temperature sensor circuit.
2. Disconnect EGR temperature sensor connector. EGR temperature sensor is mounted on EGR valve body. Read EGR gas temperature. If EGR gas temperature is not 37.6°F (3.1°C), go to next step. If EGR gas temperature is 37.6°F (3.1°C), replace sensor and retest.
3. Turn ignition off. Access ECM behind glove box. Disconnect ECM E7 connector. (Scheme 121)or (Scheme 122). Turn ignition on. Using scan tool, read EGR gas temperature. If EGR gas temperature is 37.6°F (3.1°C), locate and repair open circuit in wiring harness between ECM and EGR temperature sensor. If EGR gas temperature is not 37.6°F (3.1°C), replace ECM and retest.
4. Check EGR VSV. Using scan tool, select ACTIVE TEST mode. Check operation of EGR VSV when activated by scan tool. See appropriate illustration in «THEORY/OPERATION - 3.4L»(ref-22482) article for VSV location. Apply air pressure to EGR VSV port "E". (Scheme 124) With EGR system off, air from port "E" should flow from small filter on end of EGR VSV. With EGR system on, air from port "E" should flow from port "G". If EGR VSV operates as specified, check EGR valve. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. If EGR VSV does not operate as specified, go to next step.
5. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between EGR VSV terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each terminal and body of EGR VSV. Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
6. Check EGR VSV operation. Apply battery voltage to EGR VSV terminals. Air from port "E" should flow from small filter on end of EGR VSV. (Scheme 124) Remove battery voltage from EGR VSV terminals. Air from port "E" should flow from port "G". Replace EGR VSV as necessary. If EGR VSV operates as specified, go to next step.
7. Check for short circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace ECM and retest.

1. Disconnect EGR temperature sensor. EGR temperature sensor is mounted on EGR valve body. Using ohmmeter, measure resistance between sensor terminals. If resistance is 2500 ohms or more, go to next step. If resistance is less than 2500 ohms, replace sensor.
2. Check for short circuit in wiring harness between EGR temperature sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, go to next step.
3. Access ECM behind glove box. Ensure ignition is off. Disconnect ECM E6 connector (A/T models) or E8 connector (M/T models). Turn ignition on. On A/T models, connect a jumper wire between ground and terminal No. 8 (Red/White wire) at ECM E6 connector. On M/T models, connect a jumper wire between ground and terminal No. 18 (Red/White wire) at ECM E8 connector.
4. On all models, with jumper wire connected EGR Vacuum Switching Valve (VSV) is on. Apply air pressure to EGR VSV port "E". (Scheme 124) Air from port "E" should flow through filter on end of EGR VSV. Disconnect jumper wire. Air from port "E" should flow from port "G". If EGR VSV operates as specified, check EGR valve. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace EGR valve as necessary. If VSV does not operate as specified, go to next step.
5. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each terminal and body of EGR VSV. Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
6. Check EGR VSV operation. Apply battery voltage to EGR VSV terminals. Apply air pressure to EGR VSV port "E". (Scheme 124) Air from port "E" should flow from small filter on end of EGR VSV. Remove battery voltage from EGR VSV terminals. Air from port "E" should flow from port "G". Replace EGR VSV as necessary. If EGR VSV operates as specified, go to next step.
7. Check for short circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace ECM and retest.

1. Connect scan tool. (Scheme 121) 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-22484-S13808868582001010300000).
2. If codes other than P0420 are present, diagnose and repair those codes first. If DTC P0420 is only displayed, check oxygen sensor No. 1 circuits. See «DTC P0130»(ref-22484-S03449757142001010300000) HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test. Repair as necessary. If oxygen sensor circuits and sensor are okay, go to next step.
3. Check oxygen sensor No. 2 circuits. See «DTC P0136»(ref-22484-S30844804592001010300000) HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 2) circuit test. Repair as necessary. If oxygen sensor circuits and sensor are okay, replace catalytic converter and retest.

1. Check with vehicle driver if fuel tank cap was loose when refueling. If fuel tank cap was loose prior to refueling, it probably was cause of DTC to set. If fuel tank cap was not loose, check for cracks, deformations or loose connections in the following: Fuel tank. Charcoal canister. Fuel tank filler pipe. Hose and tubes around fuel tank and charcoal canister. Repair as necessary. If components are okay, go to next step.
2. Check if fuel tank cap is an original manufacturer's cap. If fuel tank cap is an original manufacturer's cap, go to next step. If fuel tank cap is not an original manufacturer's cap, replace cap with a manufacturer's cap.
3. Check if fuel cap is installed properly. Reinstall cap as necessary. If fuel cap is installed properly, go to next step.
4. Check for damaged fuel tank cap and gasket. Replace fuel cap as necessary. If fuel tank cap and gasket are okay, go to next step.
5. Remove fuel tank cap. Visually inspect fuel tank filler neck for damage. Replace filler neck as necessary. If filler neck is okay, go to next step.
6. Check vacuum hoses between vapor pressure sensor and VSV for vapor pressure sensor and between vapor pressure sensor and charcoal canister. Check hoses for correct installation, looseness and damage. Replace vacuum hoses as necessary. If vacuum hoses are okay, go to next step.
7. Check hose and tube between fuel tank and charcoal canister for correct installation and damage. Repair as necessary. If hose and tube are okay, go to next step.
8. Visually inspect charcoal canister for cracks or damage. Replace canister as necessary. If canister is okay, go to next step.
9. Access ECM behind glove box. Turn ignition on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 9 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On all models, if voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest.
10. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 15 (Red/Yellow wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 4 (Red/Yellow wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, disconnect vacuum hose from vapor pressure sensor. Sensor is located near brake master cylinder. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied and 1.3-2.1 volts with.59 in. Hg (2 kPa) vacuum applied, go to step 12). If voltage is not as specified, go to next step.
11. Check for open or short circuit in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace vapor pressure sensor.
12. Disconnect vacuum hose from charcoal canister. Ensure fuel tank cap is installed properly. Using compressed air, apply.71 psi (.05 kg/cm 2 ) to fuel tank. If tank does not hold pressure for a minimum of one minute, replace fuel tank. If tank holds pressure, no fault is indicated at this time. Probable cause of DTC to set was an incorrectly installed fuel tank cap.

1. Check EVAP VSV, vapor pressure sensor VSV and vapor pressure sensor wiring harness connectors for damaged pins, corrosion and loose wires. Repair as necessary. If connectors are okay, go to next step. For component locations, see appropriate illustration in «THEORY/OPERATION - 3.4L»(ref-22482) article.
2. Check all EVAP related vacuum hoses for cracks, looseness and correct routing. Replace vacuum hoses as necessary. If vacuum hoses are okay, go to next step. For proper vacuum hose routing, see appropriate illustration in «VACUUM DIAGRAMS - 3.4L»(ref-22486) article.
3. Access ECM behind glove box. Turn ignition on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 9 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On all models, if voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest.
4. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 15 (Red/Yellow wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 4 (Red/Yellow wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, disconnect vacuum hose from vapor pressure sensor. Sensor is located near brake master cylinder. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied and 1.3-2.1 volts with.59 in. Hg (2 kPa) vacuum applied, go to step 6). If voltage is not as specified, go to next step.
5. Check for open or short circuit in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace vapor pressure sensor.
6. Connect scan tool to DLC No. 3. Turn ignition. Using scan tool, select ACTIVE TEST mode. Disconnect EVAP VSV vacuum hose from charcoal canister. Start engine. Connect a vacuum gauge to disconnected vacuum hose. When EVAP VSV is activated by scan tool, vacuum should be present. When EVAP VSV is not activated, no vacuum should be present. If vacuum is as specified, go to step 9). If vacuum is not as specified, go to next step.
7. Check EVAP VSV. See EMISSION SYSTEMS & SUB-SYSTEMS in «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace VSV as necessary. If VSV is okay, go to next step.
8. Check for open or short circuit in wiring harness between EFI main relay, EVAP VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace ECM and retest.
9. Turn ignition on. Disconnect vapor pressure sensor VSV connector. VSV is mounted on top of EVAP charcoal canister. Start and run engine. Using scan tool, select ACTIVE TEST mode. On A/T models, measure voltage between terminals No. 15 (Red/Yellow wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 4 (Red/Yellow wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, with EVAP VSV activated, voltage should be 2 volts or less. If voltage is as specified, go to step 12). If voltage is not as specified, go to next step.
10. Check vapor pressure sensor VSV. See EMISSION SYSTEMS & SUB-SYSTEMS in «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace VSV as necessary. If VSV is okay, go to next step.
11. Check for open or short circuit in wiring harness between EFI main relay, vapor pressure sensor VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, go to next step.
12. Remove fuel tank cap. Disconnect vapor pressure sensor VSV connector. Select ACTIVE TEST mode on scan tool. Start engine. Using scan tool, switch EVAP VSV on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 15 (Red/Yellow wire) and No. 22 (Brown/Black wire) at ECM E7 connector 5 seconds after switching EVAP VSV from on to off.
13. On M/T models, measure voltage between terminals No. 4 (Red/Yellow wire) and No. 9 (Brown/Black wire) at ECM E7 connector 5 seconds after switching EVAP VSV from on to off. On all models, if voltage is 2.5 volts or less, replace ECM and retest. If voltage is more than 2.5 volts, replace charcoal canister.

1. Check EVAP VSV, vapor pressure sensor VSV and vapor pressure sensor wiring harness connectors for damaged pins, corrosion and loose wires. Repair as necessary. If connectors are okay, go to next step. For component locations, see appropriate illustration in «THEORY/OPERATION - 3.4L»(ref-22482) article.
2. Check all EVAP related vacuum hoses for cracks, looseness and correct routing. Replace vacuum hoses as necessary. If vacuum hoses are okay, go to next step. For proper vacuum hose routing, see appropriate illustration in «VACUUM DIAGRAMS - 3.4L»(ref-22486) article.
3. Access ECM behind glove box. Turn ignition on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 22 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, if voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest.
4. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 15 (Red/Yellow wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 4 (Red/Yellow wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, disconnect vacuum hose from vapor pressure sensor. Sensor is located near brake master cylinder. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied and 1.3-2.1 volts with.59 in. Hg (2 kPa) vacuum applied, go to step 6). If voltage is not as specified, go to next step.
5. Check for open or short circuit in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace vapor pressure sensor.
6. Access ECM behind glove box. Turn ignition on. On A/T models, connect a jumper wire between ground and terminal No. 15 (White/Green wire) at ECM E6 connector. On M/T models, connect a jumper wire between ground and terminal No. 5 (White/Green wire) at ECM E8 connector. On all models, with jumper wire connected EVAP Vacuum Switching Valve (VSV) is on. Apply air pressure to VSV port "E". (Scheme 125) Air from port "E" should flow from port "F". Disconnect jumper wire. Air from port "E" should not flow from port "F". If VSV operates as specified, go to step 10). If VSV does not operate as specified, go to next step.
7. Remove EVAP VSV. Using ohmmeter, measure resistance between VSV terminals. Resistance should be 30-34 ohms at 68°F (20°C). Measure resistance between each terminal and body of VSV. Resistance should be infinite. If resistance is not as specified, replace VSV. If resistance is as specified, go to next step.
8. Check VSV operation. Apply battery voltage to VSV terminals. Apply air pressure to VSV port "E". (Scheme 125) Air from port "E" should flow from port "F". Remove battery voltage from VSV terminals. Air from port "E" should not flow from port "F". Replace VSV as necessary. If VSV operates as specified, go to next step.
9. Check for open or short circuit in wiring harness between EFI relay, EVAP VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace ECM and retest.
10. Access ECM behind glove box. Turn ignition on. On A/T models, connect a jumper wire between ground and terminal No. 13 (Gray/Green wire) at ECM E6 connector. On M/T models, connect a jumper wire between ground and terminal No. 3 (Gray/Green wire) at ECM E8 connector. On all models, with jumper wire connected vapor pressure sensor Vacuum Switching Valve (VSV) is on. Apply air pressure to VSV port "E". (Scheme 126) Air from port "E" should flow from port "F". Disconnect jumper wire. Air from port "E" should flow from port "G". If VSV operates as specified, check charcoal canister. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. If VSV does not operate as specified, go to next step.
11. Disconnect vapor pressure sensor VSV vacuum hoses. VSV is mounted on top of EVAP charcoal canister. Using ohmmeter, measure resistance between VSV terminals. If resistance is 37-44 ohms at 68°F (20°C), go to next step. If resistance is not 37-44 ohms, replace VSV.
12. Check for continuity between each terminal and VSV body. If continuity exists, replace VSV. If continuity does not exist, apply air pressure to VSV port "E". (Scheme 126) Air from port "E" should flow from port "G". Apply battery voltage to VSV terminals. Air from port "E" should flow from port "F". If VSV operates as specified, go to next step. If VSV does not operate as specified, replace VSV.
13. Check for open or short circuit in wiring harness between EFI main relay, vapor pressure sensor VSV and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace ECM and retest.

Scheme 125

Scheme 126

1. Access ECM behind glove box. Turn ignition on. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 1 (Green/Black wire) and No. 9 (Brown/Black wire) at ECM E7 connector. (Scheme 121)or (Scheme 122). On all models, if voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest.
2. Backprobe ECM connector. On A/T models, measure voltage between terminals No. 15 (Red/Yellow wire) and No. 22 (Brown/Black wire) at ECM E7 connector. On M/T models, measure voltage between terminals No. 4 (Red/Yellow wire) and No. 9 (Brown/Black wire) at ECM E7 connector. On all models, disconnect vacuum hose from vapor pressure sensor. Sensor is located near brake master cylinder. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied and 1.3-2.1 volts with.59 in. Hg (2 kPa) vacuum applied, replace ECM and retest. If voltage is not as specified, go to next step.
3. Check for open or short circuit in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If wiring harness is okay, replace vapor pressure sensor.

1. Test drive vehicle and check operation of speedometer. If speedometer is not functioning correctly, see INSTRUMENT PANELS article in the ACCESSORIES & EQUIPMENT section. If speedometer is functioning correctly, go to next step.
2. Access ECM behind glove box. Ensure ignition is off. Disconnect cruise control ECU connector. Cruise control ECU is located behind right kick panel. Ensure shift lever is in Neutral. Lift and support rear of vehicle. Turn ignition on.
3. Using DVOM, backprobe ECM connector. On A/T models, measure voltage between ground and terminal No. 12 (Green/Orange wire) at ECM E5 connector. On M/T models, measure voltage between ground and terminal No. 8 (Green/Orange wire) at ECM E5 connector. (Scheme 121)or (Scheme 122). On all models, slowly rotate rear wheel. DVOM should indicate a pulse voltage from zero to 4-6 volts.
4. If voltage is as specified, replace ECM and retest. If voltage is not as specified, check for open circuit in wiring harness between instrument cluster and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.

1. Check 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 glove box. Disconnect ECM E8 connector. (Scheme 121)or (Scheme 122). Turn ignition on. On A/T models, measure voltage between ground and terminals No. 22 (Black/Red wire) and No. 23 (Brown/Red wire) at ECM E8 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between ground and terminals No. 6 (Black/Red wire) and No. 7 (Brown/Red wire) at ECM E8 connector. On all models, 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 127) 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 open or short circuit in wiring harness between engine compartment fuse block and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.
4. Check IAC valve operation. See «SYSTEM/COMPONENT TESTS - 3.4L»(ref-22481) article. Replace IAC valve as necessary. If valve is okay, replace ECM and retest.

Scheme 127

1. Check for spark. See IGNITION CHECKS in «BASIC TESTING - 3.4L»(ref-22485) 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 (Black/Yellow wire) between ECM and ignitor. Ignitor is located near air cleaner housing. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If circuit is okay, go to next step.
3. Disconnect Black 10-pin ignitor connector. Access ECM behind glove box. Turn ignition on. On A/T models, measure voltage between ground and terminal No. 12 (Black/Yellow wire) at ECM E8 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between ground and terminal No. 17 (Black/Yellow wire) at ECM E8 connector. On all models, if voltage is 4.5-5.5 volts, replace ignitor. If voltage is not 4.5-5.5 volts, replace ECM and retest.
4. Check for open or short in IGT1, IGT2 and IGT3 circuits between ECM and ignitor. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary. If circuits are okay, go to next step.
5. Access ECM behind glove box. On A/T models, measure voltage between ground and terminals No. 24 (Black/Blue wire), No. 25 (Brown/Yellow wire) and No. 26 (Black/White wire) at ECM E8 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between ground and terminals No. 23 (Black/Blue wire), No. 22 (Brown/Yellow wire) and No. 21 (Black/White wire) at ECM E8 connector. On all models, 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 10-pin ignitor connector. Backprobe ECM connector. On A/T models, measure voltage between ground and terminals No. 24 (Black/Blue wire), No. 25 (Brown/Yellow wire) and No. 26 (Black/White wire) at ECM E8 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between ground and terminals No. 23 (Black/Blue wire), No. 22 (Brown/Yellow wire) and No. 21 (Black/White wire) at ECM E8 connector. On all models, 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. 9 (Black/Red wire) at ignitor wiring harness connector. (Scheme 128) If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, check and repair ignitor power source circuit. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article.
8. Check for open or short circuit in wiring harness between ignition switch and ignition coil, and between ignition coil and ignitor. Repair wiring as necessary. If wiring harness is okay, check ignition coil. See IGNITION CHECKS in «BASIC TESTING - 3.4L»(ref-22485) article. Replace coil as necessary. If coil is okay, replace ignitor.

Scheme 128

1. Check stoplights. If stoplights do not function properly, repair as necessary and retest system. If stoplights function properly, go to next step.
2. Access ECM behind glove box. Locate ECM E5 connector. (Scheme 121)or (Scheme 122). Turn ignition on. Backprobe ECM connector. Measure voltage between ground and terminal No. 25 (Green/White wire) at ECM E5 connector.
3. With brake pedal depressed, voltage should be 7.5-14.0 volts. With brake pedal released, voltage should be less than 1.5 volt. If voltage is not as specified, go to next step. If voltage is as specified, check wire harness and connectors. Problem is intermittent.
4. Check for short circuit in wiring harness between ECM and stoplight switch. Repair wiring as necessary and retest system. If wiring harness is okay, replace ECM. Retest system.

1. Turn ignition off. Access ECM behind glove box. On A/T models, measure voltage between ground and terminal No. 14 (Black/Yellow wire) at ECM E5 connector. (Scheme 121)or (Scheme 122). On M/T models, measure voltage between ground and terminal No. 2 (Black/Yellow wire) at ECM E5 connector. On all models, 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. If fuse is blown, check for short circuit in wiring harness. Repair wiring as necessary and replace fuse. If fuse is okay, check circuit between EFI fuse and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring 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 129)and (Scheme 130). 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. 14 (Black wire) at ECM E8 connector. (Scheme 121)or (Scheme 122).
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 open or short circuit in wiring harness between PNP switch and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS - 3.4L»(ref-22483) article. Repair wiring as necessary.

Scheme 129

Scheme 130