Engine Controls - Tests W/codes: Diagnosis Toyota Tercel L50

MALFUNCTION INDICATOR LIGHT (MIL) INSPECTION

Note. The Malfunction Indicator Light (MIL) on the instrument panel may also be referred to as CHECK ENGINE light. Inspect MIL to ensure it is operational and will come on if a trouble code is stored.

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 panel and wiring circuit between MIL and ECM. (Scheme 34)for ECM location. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article.
2. Start engine and ensure MIL goes off. If MIL remains on with engine running, a malfunction is detected. Proceed to «RETRIEVING TROUBLE CODES»(ref-21706-S08582064092001010300000) under TESTING & REPAIR PROCEDURE.

TESTING & REPAIR PROCEDURE

The following check list of procedures is suggested to be followed to ensure correct diagnosis and repair

1. Record Customer Complaint Ensure all customer complaints or observations are recorded. Test drive vehicle with customer when necessary for malfunction verification.
2. Retrieve Trouble Codes Connect appropriate OBD-II scan tool. Retrieve codes and record any freeze-frame data. See «RETRIEVING TROUBLE CODES»(ref-21706-S08582064092001010300000) .
3. Clear Trouble Codes Clear codes using scan tool. See «CLEARING TROUBLE CODES»(ref-21706-S16085867622001010300000) .
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. See «RETRIEVING TROUBLE CODES»(ref-21706-S08582064092001010300000)
6. Diagnose & Repair Trouble Codes Perform diagnosis and repair procedures as needed. See applicable DIAGNOSTIC TESTING. If no codes are present, proceed to the «TESTS W/O CODES»(ref-21729) article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).
7. Confirmation Procedure After repairs have been completed, clear all trouble codes. See «CLEARING TROUBLE CODES»(ref-21706-S16085867622001010300000) . Perform road test. Confirm that no trouble codes are present and all symptoms and/or complaints have been repaired.

RETRIEVING TROUBLE CODES

Note. Trouble codes may be retrieved using Toyota scan tester or On-Board Diagnostic (OBD-II) scan tester that complies with SAE standard J-1978.

Normal mode is used to retrieve trouble codes from Engine Control Module (ECM). Check mode is used to check for trouble codes when operating vehicle to simulate conditions in which trouble code 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.

CLEARING TROUBLE CODES

Once repairs have been performed, codes must be cleared from ECM memory. Codes may be cleared by following methods

1. Scan tool (follow manufacturer's instructions).
2. Remove EFI fuse (15-amp) from engine compartment fuse box, near the battery, for 10 seconds or more to clear memory in ECM.
3. Disconnecting negative battery cable (memory for electronic components will be also be canceled).

TROUBLE CODE IDENTIFICATION

DLC NO. 3 INSPECTION

1. If scan tester displays UNABLE TO CONNECT TO VEHICLE when scan tester is connected, try scan tester on another vehicle. If scan tester operates on another vehicle, proceed to step 2). If scan tester does not operate on another vehicle, problem is probably with scan tester.
2. Note location of DLC No. 3 (Fig. see scheme 1 ) and its terminals (Fig. (Scheme 33) ). Ensure voltage and resistance are correct at specified terminals when checking between terminal on DLC No. 3 and body ground. See «DLC NO»(ref-21706-S31283488112001010300000). 3 VOLTAGE & RESISTANCE SPECIFICATIONS table. If voltage and resistance are not as specified, check wiring circuit. See the «WIRING DIAGRAMS»(ref-21705) article.

Note. Terminal No. 2 on DLC No. 3 provides pulse generation during information transmission from Engine Control Module (ECM).

DLC NO. 3 VOLTAGE & RESISTANCE SPECIFICATIONS

Scheme 33

Scheme 34

ECM LOCATION

DIAGNOSTIC TESTING

Note. For component location (Scheme 34)

Circuit Description

MAP sensor detects manifold pressure as a voltage that is supplied to the ECM to determine basic injection duration and advance angle. Code is set when ECM detects a open or short in MAP circuit. ECM will operate in fail-safe mode if Code P0105 is set. Possible causes are

1. MAP open or short circuit.
2. MAP sensor malfunction.
3. ECM malfunction.

Diagnosis & Repair

1. Connect scan tester to DLC3 connector. see scheme 1 Turn ignition on. Turn on scan tester. Monitor MAP value. Scan tester reading should be atmospheric pressure. If reading is within specification, inspect all connections. Problem may be intermittent. If reading is not within specification, go to next step.
2. Access ECM behind glove box. Ensure ignition is on. Using DVOM, backprobe ECM harness connector. Measure voltage between terminals VCC and E2. (Scheme 35) 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.
3. Measure voltage between ECM terminals PIM and E2. If voltage is 3.3-3.9 volts, go to next step. If voltage is not 3.3-3.9 volts, replace ECM and retest.
4. Inspect circuits between MAP and ECM for open or short. Repair as needed. If circuits are okay, replace MAP sensor.

Scheme 35

If only Code P0106 is displayed, replace MAP sensor and retest. If other codes are displayed, diagnose and repair those codes first and retest.

The IAT sensor is a thermistor mounted in the air cleaner housing to monitor air temperature flowing to intake manifold. Code is set when ECM detects a open or short circuit. ECM will operate in fail-safe mode if Code P0110 is set. Possible causes are

1. IAT sensor open or short circuit.
2. IAT sensor malfunction.
3. ECM malfunction.

Note. If Codes P0105, P0106, P0110, P0115 and P0120 are output together, inspect ECM terminal E2 (ground) circuit. Repair as needed. See wiring diagram in the WIRING DIAGRAMS article.

1. Connect scan tester to DLC3 connector. see scheme 1 Turn ignition on. Turn on scan tester. Monitor IAT sensor temperature. If temperature displayed is same as outside temperature, inspect component and ECM connections. Problem may be intermittent.
2. If temperature displayed is 284°F (140°C), go to step 5). If temperature displayed is -40°F (-40°C), turn ignition off. Disconnect IAT sensor harness connector. Using jumper wire, connect IAT harness connector terminals. Turn ignition on. Monitor IAT sensor temperature on scan tester.
3. If temperature displayed is 284°F (140°C), replace IAT sensor and retest. If temperature displayed is NOT 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM. ECM is located behind glove box. Connect jumper wire between ECM terminals E2 and THA. (Scheme 35)
4. If temperature displayed on scan tester is 284°F (140°C) or more, inspect and repair circuits between MAF harness connector and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. If temperature displayed on scan tester is NOT 284°F (140°C) or more, replace ECM and retest.
5. Turn ignition off. Disconnect IAT sensor harness connector. Turn ignition on. If temperature displayed on scan tester is -40°F (-40°C), replace IAT sensor and retest. If temperature displayed is NOT -40°F (-40°C), turn ignition off.
6. Access ECM. ECM is located behind glove box. Disconnect ECM harness connector E7. (Scheme 35) Turn ignition on. If temperature displayed is -40°F (-40°C), inspect and repair circuits between MAF sensor and ECM for short. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. If temperature displayed by scan tester is NOT -40°F (-40°C), replace ECM and retest.

The CTS sensor is a thermistor sensor that monitors water temperature. CTS sensor is located on side of cylinder head next to upper radiator hose connection. Harness connector color is Green. Code is set when ECM detects a open or short circuit. Possible causes are

1. CTS sensor open or short circuit.
2. CTS sensor malfunction.
3. ECM malfunction.

Note. If Codes P0105, P0106, P0110, P0115 and P0120 are output together, inspect ECM terminal E2 (ground) circuit. Repair as needed. See wiring diagram in the WIRING DIAGRAMS article.

1. Connect scan tester to DLC3 connector. see scheme 1 Turn ignition on. Turn on scan tester. Monitor CTS sensor temperature. If temperature displayed is same as actual coolant temperature, inspect component and ECM connections. Problem may be intermittent.
2. If temperature displayed is 284°F (140°C), go to step 5). If temperature displayed is -40°F (-40°C), turn ignition off. Disconnect CTS sensor harness connector. Using jumper wire, connect CTS harness connector terminals. Turn ignition on. Monitor CTS sensor temperature on scan tester.
3. If temperature displayed is 284°F (140°C), replace CTS sensor and retest. If temperature displayed is NOT 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM. ECM is located behind glove box. Connect jumper wire between ECM terminals E2 and THW. (Scheme 35)
4. If temperature displayed on scan tester is 284°F (140°C) or more, inspect and repair circuits for open between CTS harness connector and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. If temperature displayed on scan tester is NOT 284°F (140°C) or more, replace ECM and retest.
5. Turn ignition off. Disconnect CTS sensor harness connector. Turn ignition on. If temperature displayed on scan tester is -40°F (-40°C), replace CTS sensor and retest. If temperature displayed is NOT -40°F (-40°C), turn ignition off.
6. Access ECM. ECM is located behind glove box. Disconnect ECM harness connector E7. (Scheme 35) Turn ignition on. If temperature displayed is -40°F (-40°C), inspect and repair circuits between CTS sensor and ECM for short. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. If temperature displayed by scan tester is NOT -40°F (-40°C), replace ECM and retest.

If only Code P0116 is displayed, replace CTS and retest. If other codes are displayed, diagnose and repair those codes first and retest.

The TPS is variable resistor that monitors throttle opening. The ECM determines vehicle driving condition and adjusts air/fuel mixture accordingly. Code is set when ECM consistently detects less than .1 volt from VTA circuit and closed throttle position switch is off. Code can also be set if ECM consistently detects 4.9 volts or more. Code P0120 will not set if there is an open in IDL circuit. Possible causes are

1. TPS sensor open or short circuit.
2. TPS sensor malfunction.
3. ECM malfunction.

Note. If Codes P0110, P0115 and P0120 are output together, inspect ECM terminal E2 (ground) circuit. Repair as needed. See wiring diagram in the WIRING DIAGRAMS article.

1. Connect scan tester to DLC3 connector. see scheme 1 Turn ignition on. Turn on scan tester. Monitor throttle valve opening percentage. Opening percentage should be approximately 10 percent with fully closed throttle.
2. Depress accelerator pedal to floor (WOT). Opening percentage should be approximately 70 percent. If percentages are within specification, inspect all connections. Problem may be intermittent.
3. If percentages are NOT within specification, turn ignition off. Disconnect TPS harness connector. Turn ignition on. Using DVOM, measure voltage between harness connector terminal No. 4 and ground. (Scheme 36) If voltage measured is 4.5-5.5 volts, go to next step. If voltage is NOT 4.5-5.5 volts, go to step 8).
4. Turn ignition off. Using ohmmeter, measure resistance between TPS component connector terminals No. 1 and 4. Resistance should be 2.5-5.9 k/ohms. Measure resistance between terminals No. 1 and 3. Resistance should be.2-5.7 k/ohms with throttle fully closed and 2.0-10.2 k/ohms with throttle fully open.
5. If any resistances measured are NOT within specification, replace TPS. See the REMOVE/INSTALL/OVERHAUL article. If all resistances measured are within specification, connect TPS harness connector.
6. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals VTA and E2. (Scheme 35) Voltage should be.3-.8 volt with throttle fully closed and 3.2-4.9 volts with throttle fully open (WOT).
7. If voltages measured are within specification, replace ECM and retest. If voltages are NOT within specification, inspect VTA circuit for open or short. See wiring diagram in «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
8. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals VCC and E2. (Scheme 35) Voltage should be 4.5-5.5 volts.
9. If voltage is within specification, inspect VCC circuit for open. If voltage is NOT within specification, replace ECM and retest.

Scheme 36

If only Code P0121 is displayed, replace TPS and retest. If other codes are displayed, diagnose and repair those codes first and retest.

The oxygen sensor monitors exhaust gas oxygen content and delivers an input signal to ECM. The ECM uses input signal to determine fuel injection system operation. Sensors include heater. Code is set when sensor does not output a rich condition once engine is at normal operating temperature, engine speed of 1500 RPM or more, and vehicle speed is 25-62 MPH for at least 1.5 minutes. Possible causes are

1. Oxygen sensor open or short circuit.
2. Heated oxygen sensor malfunction.

1. Connect scan tester to DLC3 connector. see scheme 1 Start vehicle and warm engine to normal operating temperature. Turn on scan tester. Monitor front oxygen sensor. Snap accelerate engine 3 times. Sensor should indicate a rich signal (.45 volt or more).
2. If a rich signal is indicated for sensor, replace ECM and retest. If sensor does NOT display a rich signal, inspect circuits between ECM and suspect sensor for open or short circuits. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If circuits are okay, replace oxygen sensor and retest.

Test Drive Confirmation

1. Connect scan tester. see scheme 1 If using Toyota scan tester, switch to check mode. Start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 1-3 minutes. Stop vehicle and allow to idle for one minute. If malfunction exists, MIL will illuminate.
2. If using OBD-II scan tester, start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 1-3 minutes. Stop vehicle and allow to idle for one minute. Turn vehicle off. Repeat driving and idle part of test. If malfunction exists, MIL will illuminate.

1. Inspect circuits between ECM and oxygen sensor for opens or shorts. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If all circuits are okay, connect scan tester. see scheme 1
2. Start engine and warm to normal operating temperature. Monitor heated oxygen sensor output voltage and short-term fuel trim. If scan tester indicates a lean condition (.55 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), see «CODE P0170»(ref-21706-S16344857772001010300000) - FUEL TRIM MALFUNCTION.
3. If scan tester indicates other than in step 2), operate engine at 2500 RPM for 90 seconds. Monitor oxygen sensor voltage. If voltage constantly fluctuates in wide range (.3-.9 volt), repeat Test Drive Confirmation. If voltage does NOT fluctuate, or stays in narrow range, replace sensor and retest.

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

1. Access ECM harness connectors behind glove box. Turn ignition on. Using DVOM, backprobe ECM harness connector. Measure voltage between terminals HT1, HT2, and ground. (Scheme 35) Voltage for each circuit should be 9-14 volts.
2. If voltage is within specification, replace ECM and retest. If voltage is NOT within specification, turn ignition off. Disconnect oxygen sensor harness connector. Using ohmmeter, measure resistance between sensor connector terminals No. 1 and 2. (Scheme 37)
3. Resistance should be 11-16 ohms at 68°F (20°C). If resistance for sensor is within specification, inspect circuits between ECM and sensor. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If resistance is NOT within specification, replace sensor and retest.

Scheme 37

1. If any other codes are displayed other than Code P0136, diagnose and repair those codes first. If only Code P0136 is displayed, inspect circuits between ECM and sensor for opens or shorts. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
2. If all circuits are okay, connect scan tester. see scheme 1 Start and warm engine to normal operating temperature. Monitor oxygen sensor output voltage. Snap accelerate engine 3 times. Voltage should fluctuate from.4-.5 volt or more.
3. If voltage responds correctly, inspect harness connection. Problem may be intermittent. If voltage does NOT respond correctly, replace sensor and retest.

Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim. Code is set when both short-term and long-term fuel trim are lean or rich beyond a certain value. Possible causes are

1. Air intake.
2. Fuel line pressure.
3. Injector blockage or leak.
4. Heated oxygen sensor malfunction.
5. Mass airflow sensor.
6. Coolant temperature sensor.

1. Inspect all air induction components. Repair as needed. Connect scan tester. see scheme 1 Start engine and warm to normal operating temperature. Monitor heated oxygen sensor output voltage and short-term fuel trim.
2. If scan tester indicates a lean condition (.55 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), go to next step. If results are other than shown, see «CODE P0130»(ref-21706-S25810345642001010300000) - HEATED OXYGEN SENSOR (FRONT SENSOR) CIRCUIT.
3. Inspect fuel pressure. See the «BASIC TESTING»(ref-21589) article. Repair as needed. If fuel pressure is okay, inspect fuel injector performance. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed.
4. If all injectors are okay, inspect Mass Airflow (MAF) sensor and Coolant Temperature Sensor (CTS). See procedures in the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. If both components are okay, inspect ignition system. See procedures in the «BASIC TESTING»(ref-21589) article. Repair as needed. 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.

Code 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. Coolant Temperature Sensor (CTS).

1. Inspect spark plugs and ignition system. See procedures in the «BASIC TESTING»(ref-21589) article. Repair as needed. If ignition system is okay, ensure ignition is off.
2. Access ECM harness connectors behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between individual terminals #10, #20, and ground. (Scheme 35) If voltage is 9-14 volts for each circuit, go to step 4). If voltage is NOT 9-14 volts, go to next step.
3. Disconnect injector of misfiring cylinder. Using ohmmeter, measure resistance between injector terminals. If resistance is 13.4-14.2 ohms, inspect circuits between ECM and injector for open or short. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If resistance is NOT 13.4-14.2 ohms, replace injector.
4. Inspect fuel pressure. See the «BASIC TESTING»(ref-21589) article. Repair as needed. If fuel pressure is okay, inspect fuel injector performance. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed.
5. If all injectors are okay, inspect EGR system. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Repair as needed. If EGR system is okay, inspect MAP sensor and CTS. See the SYSTEM/COMPONENT TESTS article. Replace as needed. If both components are okay, also inspect engine compression, valve clearance and valve timing. See the «BASIC TESTING»(ref-21589) article.

See CODE P0300 - RANDOM/MULTIPLE MISFIRE DETECTED.

See CODE P0300 - RANDOM/MULTIPLE MISFIRE DETECTED.

Knock sensor is located on cylinder block below coolant pipe. Sensor generates voltage when engine block vibrates due to knocking. Code is set when there is no knock sensor signal to ECM with engine speed of 2000 RPM or more. Possible causes are

1. Open or short in knock sensor circuit.
2. Knock sensor (loose).
3. ECM.

1. Ensure ignition is off. Access ECM behind glove box. Disconnect ECM connector E7. Using ohmmeter, measure resistance between terminal KNK and ground. If resistance is infinite, go to next step. If resistance is NOT infinite, go to step 3).
2. Disconnect knock sensor harness connector. Measure resistance between sensor terminal and sensor housing. If resistance is infinite, go to next step. If resistance is NOT infinite, replace sensor.
3. Inspect circuit between knock sensor and ECM for open or short. Repair as needed. If circuit is okay, substitute knock sensor with known good sensor and retest. If Code P0325 is still present, replace ECM and retest. If code is no longer present, replace sensor.

The CKP sensor is a pick-up coil mounted next to crankshaft. A 34-tooth signal plate is mounted to crankshaft. Code is set when either no cranking or engine running signal is received by ECM from sensor. Possible causes are

1. CKP sensor open or short circuit.
2. CKP sensor.
3. Starter.
4. ECM.

1. Disconnect CKP sensor harness connector. Using ohmmeter, measure resistance between sensor connector terminals No. 1 and 2. (Scheme 38) Resistance should be 985-1600 ohms (cold sensor) or 1265-1 890 ohms (hot sensor).
2. Replace sensor as needed. If sensor is okay, inspect circuits between ECM and CKP sensor for open or short. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If both circuits are okay, remove sensor and inspect. Also inspect signal plate. Replace as needed. If both components are okay, replace ECM and retest.

Scheme 38

The CMP sensor is a pick-up coil mounted in cylinder head. A 1-tooth signal plate is mounted to exhaust camshaft. Code is set when either no cranking or engine running signal is received by ECM from sensor. Possible causes are

1. CMP sensor open or short circuit.
2. CMP sensor.
3. Distributor.
4. Starter.
5. ECM.

1. Disconnect CMP harness connector. Using ohmmeter, measure resistance between connector terminals. (Scheme 39) Resistance should be 985-1600 ohms (cold sensor) or 1265-1890 ohms (hot sensor).
2. Replace sensor as needed. If sensor is okay, inspect circuits between ECM and sensor for open or short. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
3. If both circuits are okay, inspect sensor installation. If sensor is not okay, replace CMP sensor. If sensor is okay, replace ECM and retest.

Scheme 39

The EGR system recirculates exhaust gas through intake system to reduce combustion temperature and NOx emissions. The amount of EGR valve opening is regulated by the EGR vacuum modulator according to engine load. Vacuum source to valve is controlled by the Vacuum Switching Valve (VSV), which is operated by ECM.

The EGR valve is closed (VSV on) under the following conditions

1. Coolant temperature 122°F (50°C).
2. Vehicle under deceleration.
3. Light engine load.
4. Engine idling.
5. Engine racing.
6. High engine load.

Code is set when intake manifold absolute pressure is greater than the value calculated by ECM while the EGR system is on. Possible causes are

1. EGR valve stuck closed.
2. VSV open or short circuit.
3. EGR vacuum hose disconnected.
4. MAP sensor.
5. EGR VSV.
6. ECM.

1. Connect scan tester. see scheme 1 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". May also be known as I/M flag. If COMPL is displayed on scan tester and MIL is not illuminated, system is normal. If INCPL is displayed and MIL is not illuminated, repeat test drive procedure.

Diagnosis & Repair (Toyota Scan Tester ONLY)

1. Inspect EGR vacuum hose. Connect scan tester. see scheme 1 Turn ignition on. On scan tester, select active test mode. Check operation of VSV when activated by scan tester. VSV is located on cylinder head, below EGR vacuum modulator.
2. Start and run engine. With system in OFF mode, air should flow through valve. With system in ON mode, air should NOT flow through valve. If valve operates correctly, go to step 6). If valve does NOT operate correctly, go to next step.
3. 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 valve. Resistance should be infinite. Replace VSV as needed.
4. Check VSV operation. Apply battery voltage to valve terminals. Air should flow through valve. Remove battery voltage from valve terminals. Air should NOT flow through valve. Replace as needed.
5. If valve meets all specifications in steps 3) and 4), inspect circuits between EGR VSV and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
6. Inspect EGR vacuum modulator. See procedures in the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. Inspect EGR valve. See the SYSTEM/COMPONENT TESTS article. Replace as needed.
7. Inspect MAP sensor. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. If sensor is okay, replace ECM and retest.

Diagnosis & Repair (OBD-II Scan Tester ONLY)

1. Inspect all EGR system vacuum hoses. Replace as needed. Check operation of EGR Vacuum Switching Valve (VSV). Access ECM. ECM is located behind glove box. Ensure ignition is off. Disconnect E6 harness connector. Turn ignition on. Using jumper wire, connect ECM terminal EGR to ground.
2. VSV is located on cylinder head, below EGR vacuum modulator. With jumper wire connected, VSV is on. Air should flow through valve. Disconnect jumper wire. Air should NOT flow through valve. If valve operates correctly, go to step 6).
3. If valve does operate correctly, 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 valve. Resistance should be infinite. Replace VSV as needed.
4. Check VSV operation. Apply battery voltage to valve terminals. Air should flow through valve. Remove battery voltage from valve terminals. Air should NOT flow through valve. Replace as needed.
5. If valve meets all specifications in steps 3) and 4), inspect circuits between EGR VSV and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
6. Inspect EGR vacuum modulator. See procedures in the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. Inspect EGR valve. See the SYSTEM/COMPONENT TESTS article. Replace as needed.
7. Inspect MAP sensor. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. If sensor is okay, replace ECM and retest.

See CODE P0401 - INSUFFICIENT EXHAUST GAS RECIRCULATION (EGR) FLOW DETECTED. Code is set when intake manifold absolute pressure is greater than the value calculated by the ECM while the EGR system is on and misfiring is detected during idling. Possible causes are

1. EGR valve stuck open.
2. EGR Vacuum Switching Valve (VSV).
3. MAP sensor.
4. ECM.

1. Connect scan tester. see scheme 1 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". May also be known as I/M flag. If COMPL is displayed on scan tester and MIL is not illuminated, system is normal. If INCPL is displayed and MIL is not illuminated, repeat test drive procedure.

1. Inspect EGR vacuum hoses. Replace as needed. Inspect EGR valve. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Inspect EGR VSV. On scan tester, select active test mode. Check operation of VSV when activated by scan tester. VSV is located on cylinder head below EGR vacuum modulator.
2. Start and run engine. With system in OFF mode, air should flow through valve. With system in ON mode, air should not flow through valve. If valve operates correctly, go to step 4). If valve does NOT operate correctly, go to next step.
3. 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 valve. Resistance should be infinite. Replace VSV as needed.
4. Check VSV operation. Apply battery voltage to valve terminals. Air should flow through valve. Remove battery voltage from valve terminals. Air should NOT pass through valve. Replace as needed.
5. If valve meets all specifications in steps 3) and 4), inspect circuits for short between EGR VSV and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
6. Inspect EGR vacuum modulator. See procedures in the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. Inspect MAP sensor. See the SYSTEM/COMPONENT TESTS article. Replace as needed. If sensor is okay, replace ECM and retest.

1. Inspect all EGR system vacuum hoses. Replace as needed. Inspect EGR valve. See the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed.
2. Check operation of EGR Vacuum Switching Valve (VSV). Access ECM. ECM is located behind glove box. Ensure ignition is off. Disconnect E6 harness connector. Turn ignition on. Using jumper wire, connect ECM terminal EGR to ground.
3. VSV is located on cylinder head, below EGR vacuum modulator. With jumper wire connected, VSV is on. Air should flow through valve. Disconnect jumper wire. Air should NOT flow through valve. If valve operates correctly, go to step 7).
4. If valve does operate correctly, 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 valve. Resistance should be infinite. Replace VSV as needed.
5. Check VSV operation. Apply battery voltage to valve terminals. Air should flow through valve. Remove battery voltage from valve terminals. Air should NOT flow through valve. Replace as needed.
6. If valve meets all specifications in steps 4) and 5), inspect circuits between EGR VSV and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
7. Inspect EGR vacuum modulator. See procedures in the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. Inspect MAP sensor. See the SYSTEM/COMPONENT TESTS article. Replace as needed. If sensor is okay, replace ECM and retest.

The ECM compares waveform of oxygen sensor located before catalytic converter with waveform of oxygen sensor located after converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. Code is set when all oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 19-52 MPH. Possible causes are

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

1. Connect scan tester. see scheme 1 Start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 5-10 minutes. Stop vehicle. Retrieve codes. See «RETRIEVING TROUBLE CODES»(ref-21706-S08582064092001010300000).
2. If codes other than P0420 are present, diagnose and repair those codes first. If Code P0420 is only displayed, inspect oxygen sensor circuits. See «CODE P0130»(ref-21706-S25810345642001010300000) - HEATED OXYGEN SENSOR (FRONT SENSOR) CIRCUIT. Repair systems as needed. If oxygen sensor circuits and sensors are okay, replace catalytic converter and retest.

Vehicle Speed Sensor (VSS), driven by speedometer cable, outputs a signal from combination meter to ECM. Combination meter converts signal to a more precise waveform for ECM. Code is set when ECM does not detect any signal while vehicle is in motion. Possible causes are

1. Combination meter.
2. Speed sensor open or short circuit.
3. ECM.
4. Speedometer cable.

1. Test drive vehicle and check operation of speedometer. If speedometer is not functioning correctly, see the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. If speedometer is functioning correctly, go to next test.
2. Access ECM behind glove box. Ensure ignition is off. Ensure shift lever is in neutral. Lift and support front of vehicle. Turn ignition on.
3. Using DVOM, backprobe ECM connector. Measure voltage between terminal SPD and ground, while slowly rotating front wheel. (Scheme 35) DVOM should indicate a pulse voltage from zero to 4.5-5.5 volts.
4. If voltage is within specification, replace ECM and retest. If voltage is not within specification, inspect for possible open circuit between combination meter and ECM. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.

The ECM operates only IAC valve to perform idle-up and provide feedback for target idling speed. A Vacuum Switching Valve (VSV) is added for idle compensation when A/C is operated. Code is set when idle speed continues to vary greatly from target speed. Possible causes are

1. Idle Air Control (IAC) valve stuck or closed.
2. IAC valve circuit open or short.
3. AC1 open or short circuit.
4. Air intake leak.

1. Inspect air induction system for leaks. Repair as needed. Inspect A/C signal circuit. See the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
2. Ensure ignition if off. Access ECM. ECM is located behind glove box. Disconnect ECM harness connector E7. Turn ignition on. Using DVOM, measure voltage between individual connector terminals RSO, RSC, and ground. (Scheme 35) Voltage should be 9-14 volts for both circuits.
3. If voltage is within specification, go to step 5). If voltage is NOT within specification, turn ignition off. Disconnect IAC valve harness connector. IAC valve is located in front of throttle body at 6 o'clock position. Using ohmmeter, measure resistance between component terminals. (Scheme 40)
4. For resistance specifications, see «IAC RESISTANCE»(ref-21706-S04102271662001010300000) table. If resistances measured are NOT within specification, replace IAC valve. If resistances are within specification, inspect circuits between IAC and ECM for opens or shorts. Repair as needed. IAC RESISTANCE Terminals No. Ohms 1 & 2 10-30 2 & 3 10-30
5. Inspect operation of IAC valve. Remove valve. To inspect valve, see the «SYSTEM/COMPONENT TESTS»(ref-21636) article. Replace as needed. If valve is okay, replace ECM and retest.

Scheme 40

Built into Throttle Position Sensor (TPS), the closed throttle position switch turns off whenever the throttle position is NOT fully closed. Code is set when ECM never receives a ON signal from switch. Possible causes are

1. Closed throttle position switch open circuit.
2. Closed throttle position switch.
3. ECM.

Note. If trouble Codes P0105, P0106, P0110, P0115 and P0120 are output simultaneously, ground (E2) circuit may be open.

1. Connect scan tester. see scheme 1 Disconnect TPS harness connector. Using jumper wire, connect wire to TPS harness connector terminals No. 1 and 2. (Scheme 36)
2. Turn ignition on. Read CTP switch signal on scan tester. If CTP switch signal displayed is ON, replace TPS and retest. If signal displayed is OFF, go to next step.
3. Turn ignition off. Remove jumper wire. Access ECM. ECM is located behind glove box. Connect jumper wire between ECM connector terminals IDL and E2. (Scheme 35) Turn ignition on. Read CTP switch signal on scan tester. If CTP switch signal displayed is ON, inspect circuits between TPS and ECM. Repair as needed. If signal displayed is OFF, replace ECM and retest.

1. Ensure ignition is off. Disconnect TPS harness connector. Turn ignition on. Using DVOM, measure voltage between terminals No. 1 and 2. (Scheme 36) If voltage is 9-14 volts, replace TPS and retest. If voltage is NOT 9-14 volts, go to next step.
2. Turn ignition off. Inspect circuits between TPS and ECM for open. Repair as needed. If circuits are okay, replace ECM and retest.

The ECM uses pick-up coil input signals to switch primary ignition circuit on and off. Primary circuit is turned off when ECM delivers a signal to ignitor on the IGT wire, causing ignition coil to fire spark plug. After delivering a command to turn off primary circuit on IGT wire, the ECM monitors IGF circuit to ensure primary switching occurred. Code is set when there is no IGF signal to ECM for 6 consecutive IGT signals during engine operation. Possible causes are

1. IGF or IGT open or short circuit from ignitor to ECM.
2. Ignitor.
3. ECM.

1. Inspect for spark at plugs. Remove wire from individual spark plug. Remove spark plug and insert into wire. Disconnect appropriate injector harness connector. Ground spark plug and crank engine. Ensure spark is present.
2. If spark does not exist, go to step 5). If spark does exist, inspect IGF circuit between ignitor and ECM for short or open. (Scheme 35)and (Scheme 41). See the wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article.
3. Repair as needed. If circuit is okay, disconnect ignitor connector. Ignitor is in back of air cleaner housing. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector.
4. Measure voltage between terminal IGF and ground. (Scheme 35) If voltage is 4.5-5.5 volts, replace ignitor and retest. If voltage is not 4.5-5.5 volts, replace ECM and retest.
5. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between terminal IGT1, IGT2 of ECM connector, and ground while cranking engine. Voltage should be.5-1.0 volt for each circuit.
6. If voltage is within specification, go to next step. If voltage NOT within specification, go to step 10).
7. Disconnect ignitor connector. Ignitor is mounted to left side of firewall. Measure voltage between ignitor harness connector terminal No. 7 and ground. (Scheme 41) Turn ignition switch to ON position. Voltage should be 9-14 volts. Turn ignition switch to START position. Voltage should be 9-14 volts.
8. If voltage is NOT within specification, inspect ignitor power supply circuit. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.
9. If voltage is within specification, check for open or short in harness between ignition switch and ignition coil, ignition coil and ignitor. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If circuits are okay, inspect ignition coil. See the «BASIC TESTING»(ref-21589) article. Replace as needed. If coil is okay, replace ignitor and retest.
10. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector. Ensure ignitor connector is disconnected. Measure voltage between individual terminals IGT1, IGT2 of ECM connector, and ground while cranking engine. (Scheme 35) Voltage should be.5-1.0 volt for each circuit.
11. If voltages are within specification, replace ignitor and retest. If voltages are NOT within specification, inspect IGT1, IGT2 circuits between ignitor and ECM for opens or shorts. Repair as needed. If circuits are okay, replace ECM and retest.

Scheme 41

See CODE P0335 - CRANKSHAFT POSITION (CKP) SENSOR "A" CIRCUIT. Code is set when ECM receives no CKP sensor signal with engine speed of 1000 RPM or more. Possible causes are

1. CKP sensor open or short circuit.
2. CKP sensor.
3. Starter.
4. ECM.

See CODE P0335 - CRANKSHAFT POSITION (CKP) SENSOR "A" CIRCUIT.

While engine is being cranked, battery voltage is applied to ECM terminal STA. Signal is mainly used to increase fuel injection volume for starting injection control and after-start injection control. Code is set when ECM does not receive starter signal. Possible causes are

1. Starter signal open or short circuit.
2. Ignition switch or starter relay open or short circuit.
3. ECM.

Note. Scan tester diagnosis can only be attempted with Toyota scan tester operated in check mode.

1. Connect Toyota scan tester. see scheme 1 Turn ignition and scan tester on. Read STA signal on scan tester. Turn ignition switch to START position and release.
2. STA signal should be OFF with ignition switch in ON position. STA signal should be ON with ignition switch in START position. If STA signal is correct as shown, inspect all applicable connectors. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Malfunction may be intermittent.
3. If STA signal is NOT as specified in step 2), inspect circuit between starter relay and ECM for open. See wiring diagram in the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed. If circuit is okay, replace ECM and retest.

Battery voltage is supplied to ECM BATT terminal (constant). Code is set when open in back-up power source is detected. Possible causes are

1. Back-up power source open circuit.
2. ECM.

1. Ensure ignition is off (LOCK position). Access ECM. ECM is located behind glove box. Using DVOM, measure voltage between BATT terminal of ECM connector and ground. (Scheme 35) If voltage is 9-14 volts, replace ECM and retest. If voltage is NOT 9-14 volts, go to next test.
2. Remove and inspect EFI fuse. EFI fuse is located in engine compartment fuse box. Replace as needed. If fuse is okay, inspect circuit between EFI fuse and ECM. See the «WIRING DIAGRAMS»(ref-21705) article. Repair as needed.

See CODE P0325 - KNOCK SENSOR NO. 1 CIRCUIT. Code is set when ECM is detected to be faulty in regard to knock control. ECM is the only possible cause.

If any codes other than Code P1605 are displayed, diagnose and repair those codes first. If only Code P1605 is displayed, replace ECM and retest.

The PNP switch sends a signal to ECM when transmission is in Neutral or Park position. This signal is used for air/fuel correction and for idle speed control. Code is set under 2 conditions

1. When 2 or more switches are on simultaneously for "N", "2" and "L" position.
2. ECM is receiving an ON signal from PNP switch when vehicle is being operated for more than 30 seconds at 44 MPH or more (1500-2500 RPM).

1. Disconnect PNP switch harness connector. PNP switch is located at transmission where shifter select cable is mounted. Using ohmmeter, check continuity of switch terminals in specified positions. (Scheme 42)and (Scheme 43). Replace as needed.
2. If switch is okay, Access ECM. ECM is located behind glove box. Turn ignition on. Using DVOM, measure voltage between terminal NSW and ground. (Scheme 35)
3. Voltage should be 0-3 volts in "P" or "N" position. Voltage should be 9-14 volts in any other shift selector position. If all voltages measured are within specifications, replace ECM and retest.
4. If any voltages measured are NOT within specifications, inspect circuit between PNP switch and ECM for open or short. Repair as needed.

Scheme 42

Scheme 43