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

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»(ref-22341) article. See «ECM LOCATION»(ref-22343-S23493403542001010300000) .
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-22343-S02991139372001010300000) .

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-22343-S02991139372001010300000) .
3. Clear Trouble Codes Clear codes. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-22343-S17007972162001010300000) .
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-22343-S29949039282001010300000) . If no codes are present, proceed to «TESTS W/O CODES - 1.6L»(ref-22344) 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-22343-S17007972162001010300000) . 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-22343-S27064370912001010300000) 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 - 1.6L»(ref-22344) article for diagnosis by symptom.
5. If any DTCs are present, perform appropriate circuit test. See «DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION»(ref-22343-S19578978792001010300000) table. For more information on freeze-frame data, see «FREEZE-FRAME DATA»(ref-22343-S25246688922001010300000) under INTRODUCTION. For information on 2-trip detection logic codes, see «TWO-TRIP DETECTION LOGIC»(ref-22343-S19914065232001010300000) under INTRODUCTION.
6. After repairs for DTC have been completed, DTC must be cleared from ECM memory. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-22343-S17007972162001010300000) .

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.

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-22343-S29949039282001010300000) .

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»(ref-22341) 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. 3 VOLTAGE & RESISTANCE SPECIFICATIONS table. (Scheme 31) If voltage and resistance readings are not as specified, check wiring circuit. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article.

DLC NO. 3 VOLTAGE & RESISTANCE SPECIFICATIONS

Scheme 31

Diagnosis & Repair

If any 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 tool to DLC No. 3 connector. see scheme 2 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 IAT sensor connector. Connect a jumper wire between IAT sensor wiring harness connector terminals. Turn ignition on. Using scan tool, monitor IAT sensor temperature.
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 tool 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»(ref-22341) article. Repair wiring as necessary. If temperature displayed on scan tool 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 tool 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), check and repair wiring harness between IAT sensor and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) 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. see scheme 2 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. 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 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 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 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 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), locate and repair short circuit in wiring harness between ECT sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If temperature displayed by scan tool 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 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. see scheme 2 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 70 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. 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 - 1.6L»(ref-22342) 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»(ref-22341) article. Repair wiring 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 tool to DLC No. 3 connector. see scheme 2 Start vehicle and warm engine to normal operating temperature. Using scan tool, 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, check for open or short in wiring harness between ECM and oxygen sensor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) 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. see scheme 2 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.

Diagnosis & Repair Procedure

1. Check for open or short circuit in wiring harness between ECM and oxygen sensor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary. If wiring harness is okay, connect scan tool. see scheme 2
2. Start engine and warm to normal operating temperature. Monitor 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-22343-S04894122742001010300000) 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. Allow engine to idle and 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. 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 in wiring harness between ECM and oxygen sensor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary.
2. If wiring harness is okay, connect scan tool. see scheme 2 Start and warm engine to normal operating temperature. Using scan tool, monitor sensor No. 2 output voltage. Snap accelerate engine 3 times. Voltage should fluctuate from.4 volt or less to.5 volt or more.
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. 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 or Black wire) at oxygen sensor connector.
3. If resistance is 11-16 ohms at 68°F (20°C), check circuits between ECM and sensor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary. If resistance is not 11-16 ohms, replace sensor and retest.

1. Check all air induction components. Repair as necessary. If air induction components are okay, connect scan tool. see scheme 2 Start engine and warm to normal operating temperature. Monitor heated oxygen sensor 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-22343-S40980877602001010300000) OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test.
3. Check fuel pressure. See «BASIC TESTING»(ref-22339) article. Repair fuel pressure as necessary. If fuel pressure is okay, check fuel injectors. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace injectors as necessary.
4. If all injectors are okay, check Manifold Absolute Pressure (MAP) sensor and Engine Coolant Temperature (ECT) sensor. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If both components are okay, check ignition system. See IGNITION CHECKS in «BASIC TESTING»(ref-22339) article. Repair ignition system 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-22339) 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-22343-S29837117532001010300000) 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 11 Black/Red 3 25 Black/White 4 24 Black (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), check for open or short circuit in wiring harness between ECM and injector. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary. If resistance is not 13.4-14.2 ohms, replace injector.
4. Check fuel pressure. See «BASIC TESTING»(ref-22339) article. Repair fuel pressure as necessary. If fuel pressure is okay, check fuel injector performance. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace fuel injectors as necessary.
5. If all injectors are okay, check EGR system. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Repair EGR system as necessary. If EGR system is okay, check MAP sensor and ECT sensor. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If both components are okay, also check engine compression, valve clearance and valve timing. See «BASIC TESTING»(ref-22339) article.

See DTC P0300 RANDOM MISFIRE DETECTED circuit test.

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. If resistance is not as specified, replace CKP sensor. If resistance is as specified, check for open or short circuit in wiring harness between ECM and CKP sensor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) 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.

If only DTC P0336 is displayed, replace ECM and retest. If other codes are displayed, diagnose and repair those codes first and retest.

1. Disconnect CMP sensor connector. Measure resistance between terminals G+ and G- at CMP sensor connector. (Scheme 32) Resistance should be 185-275 ohms (cold sensor) or 240-325 ohms (hot sensor).
2. If resistance is not as specified, replace CMP sensor. If resistance is as specified, check for open or short circuit in wiring harness between ECM and CMP sensor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary.
3. If wiring harness is okay, inspect CMP sensor installation. Repair as necessary. If installation is okay, replace ECM and retest.

Scheme 32

1. Connect scan tool. see scheme 2 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. Check vacuum hoses. See appropriate illustration in «VACUUM DIAGRAMS»(ref-22345) article. Repair vacuum hoses as necessary. If all hoses are okay, check VSV. Using scan tool, select ACTIVE TEST mode. Check operation of VSV when activated by scan tool. VSV is mounted on top right rear of engine.
2. Start and run engine. With EGR system off, air from port "E" should flow from small filter on end of valve. (Scheme 33) With EGR system on, air from port "E" should flow 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. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". (Scheme 33) Remove battery voltage from valve terminals. Air from port "E" should flow from small filter on end of valve. Replace VSV as necessary. If VSV operates as specified, go to next step.
5. Check for open or short circuit in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary.
6. Check EGR vacuum modulator. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If modulator is okay, check EGR valve. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If components are okay, go to next step.
7. Check Manifold Absolute Pressure (MAP) sensor. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.

Scheme 33

Diagnosis & Repair (Using OBD-II Scan Tool)

1. Check all EGR system vacuum hoses. Replace vacuum hoses 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. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". (Scheme 33) Disconnect jumper wire. Air from port "E" should flow 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. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". (Scheme 33) Remove battery voltage from valve terminals. Air from port "E" should flow from small filter on end of valve. Replace VSV as necessary.
5. Check for open or short circuit in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary.
6. Check EGR vacuum modulator. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If EGR valve is okay, go to next step.
7. Check Manifold Absolute Pressure (MAP) sensor. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.

1. Connect scan tool. see scheme 2 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.

1. Check all EGR system vacuum hoses. Replace vacuum hoses as necessary. If vacuum hoses are okay, check EGR valve. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) 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. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". (Scheme 33) Disconnect jumper wire. Air from port "E" should flow from small filter on end of VSV. If valve operates as specified, go to step 7). If valve does not 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. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". (Scheme 33) Remove battery voltage from valve terminals. Air from port "E" should flow from small filter on end of valve. Replace VSV as necessary.
6. Check for open or short circuit in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair as necessary.
7. Check EGR vacuum modulator. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace as necessary. If EGR valve is okay, go to next step.
8. Check Manifold Absolute Pressure (MAP) sensor. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.

1. If codes other than P0420 are present, diagnose and repair those codes first. If DTC P0420 is only displayed, check oxygen sensor No. 1. See «DTC P0130»(ref-22343-S40980877602001010300000) OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test. Repair as necessary. If oxygen sensor circuits are okay, go to next step.
2. Check oxygen sensor No. 2 circuits. See «DTC P0136»(ref-22343-S17720812192001010300000) 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. 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. 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, check Violet/White wire between instrument cluster and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair wiring as necessary.

Repair & Diagnosis

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 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 34) 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»(ref-22341) article. Repair wiring as necessary.
4. Check IAC valve operation. See «SYSTEM/COMPONENT TESTS - 1.6L»(ref-22342) article. Replace IAC valve as necessary. If valve is okay, replace ECM and retest.

Scheme 34

1. Check for spark at misfiring cylinder. See IGNITION CHECKS in «BASIC TESTING»(ref-22339) 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 ignitor. Ignitor is located in left side of engine compartment. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. Repair as necessary. If circuit is okay, go to next step.
3. Disconnect Black 5-pin ignitor 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 ignitor. 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 ignitor. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) article. 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 ignitor 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 ignitor wiring harness connector. (Scheme 35) 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»(ref-22341) article.
8. Check for an open or short in wiring harness between ignition switch and ignition coil, and between ignition coil and ignitor. Repair wiring as necessary. If wiring is okay, check ignition coil. See IGNITION CHECKS in «BASIC TESTING»(ref-22339) article. Replace coil as necessary. If coil is okay, replace ignitor.

Scheme 35

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, check wiring harness between EFI fuse and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-22341) 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 36)and (Scheme 37). 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»(ref-22341) article. Repair wiring as necessary.

Scheme 36

Scheme 37