Engine Controls - Tests W/codes: Diagnosis Toyota Avalon XX10

MALFUNCTION INDICATOR LIGHT 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 37)for ECM location. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) 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-21645-S24654606282001010300000) 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-21645-S24654606282001010300000) .
3. Clear Trouble Codes Clear codes using scan tool. See «CLEARING TROUBLE CODES»(ref-21645-S01100285462001010300000) .
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-21645-S24654606282001010300000)
6. Diagnose & Repair Trouble Codes Perform diagnosis and repair procedures as needed. See applicable DIAGNOSTIC TESTING. If no codes are present, proceed to «TESTS W/O CODES»(ref-21723) 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-21645-S01100285462001010300000) . 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-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 next step. If scan tester does not operate on another vehicle, problem is probably with scan tester.
2. Note location of DLC-3 and its terminals. see scheme 1and (Scheme 36). Ensure voltage and resistance are correct at specified terminals when checking between terminal on DLC-3 and body ground. See «DLC-3 VOLTAGE & RESISTANCE SPECIFICATIONS»(ref-21645-S06771989382001010300000) table. If voltage and resistance are not as specified, check wiring circuit. See «WIRING DIAGRAMS»(ref-21644) article.

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

DLC-3 VOLTAGE & RESISTANCE SPECIFICATIONS

Scheme 36

Scheme 37

ECM LOCATION

DIAGNOSTIC TESTING

Note. For component location (Scheme 37)

Circuit Description

Mass Airflow (MAF) sensor uses a platinum hot wire maintained at a constant temperature. Airflow past sensor affects temperature and current flow through sensor. Code is set when ECM detects an open or short circuit with engine speed of 4000 RPM or less. ECM will operate in fail-safe mode if Code P0100 is set. Possible causes are

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

Diagnosis & Repair

1. Connect scan tester to DLC-3 connector. see scheme 1 Start vehicle engine and allow to idle. Turn on scan tester. Monitor MAF flow rate. If scan tester reading is 0.0 gm/sec., go to next step. If reading is 9.0-21.0 gm/sec. once engine is at normal operating temperature, go to step 5.
2. Disconnect MAF harness connector. Ensure ignition is on. Using DVOM, measure voltage between terminal No. 1 and ground. (Scheme 38) If 9-14 volts is present, go to next step. If 9-14 volts is NOT present, inspect circuit between MAF harness connector and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.
3. Access ECM behind glove box. Start engine. Backprobing ECM connector, check voltage between terminal "VG" and ground. (Scheme 39) 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 between MAF and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuit is okay, replace MAF sensor and retest.
5. Access ECM behind glove box. Turn ignition off. Using ohmmeter, backprobe ECM harness connector. Check continuity between terminal "VG-" and ground. (Scheme 39) If continuity does NOT exist, replace ECM and retest. If continuity does exist, check for open circuit between MAF sensor and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuit is okay, replace MAF sensor.

Scheme 38

Scheme 39

Diagnosis & Repair Procedure

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

Intake Air Temperature (IAT) sensor is a thermistor built into the MAF sensor to monitor air temperature flowing through MAF sensor. 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 P0110, P0115 and P0120 are output together, inspect ECM connector "E7" terminal No. 22 "E2" (ground) circuit. Repair as needed. See wiring diagram in WIRING DIAGRAMS article.

1. Connect scan tester to DLC-3. 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 is 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 MAF sensor harness connector. Using jumper wire, connect MAF harness connector terminals No. 3 and 4. (Scheme 38) Turn ignition on. Monitor IAT sensor temperature on scan tester.
3. If temperature displayed is 284°F (140°C), replace MAF sensor and retest. If temperature displayed is NOT 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM behind glove box. Connect jumper wire between ECM connector "E7" terminal No. 22 (E2) and No. 21 (THA). (Scheme 39)
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-21644) article. If temperature displayed on scan tester is NOT 284°F (140°C) or more, replace ECM and retest.
5. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on. If temperature displayed on scan tester 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 harness connector "E7". (Scheme 39) 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-21644) article. If temperature displayed by scan tester is NOT -40°F (-40°C), replace ECM and retest.

Coolant Temperature Sensor (CTS) is a thermistor sensor that monitors water temperature. 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 P0110, P0115 and P0120 are output together, inspect ECM terminal "E2" (ground) circuit. Repair as needed. See wiring diagram in WIRING DIAGRAMS article.

1. Connect scan tester to DLC-3. see scheme 1 Turn ignition on. Turn on scan tester. Monitor CTS temperature. If temperature displayed is same as actual coolant temperature, inspect component and ECM connections. Problem is intermittent.
2. If temperature displayed is 284°F (140°C), go to step 5. If temperature displayed is -40°F (-40°C), turn ignition off. Disconnect CTS harness connector. CTS is located in thermostat housing. Using jumper wire, connect CTS harness connector terminals. Turn ignition on. Monitor CTS temperature on scan tester.
3. If temperature displayed is 284°F (140°C), replace CTS and retest. If temperature displayed is NOT 284°F (140°C), turn ignition off. Remove jumper wire. Access ECM behind glove box. Connect jumper wire between ECM harness connector "E7" terminals No. 22 (E2) and No. 20 (THW). (Scheme 39)
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 «WIRING DIAGRAMS»(ref-21644) 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 harness connector. Turn ignition on. If temperature displayed on scan tester is -40°F (-40°C), replace CTS and retest. If temperature displayed is NOT -40°F (-40°C), turn ignition off.
6. Access ECM behind glove box. Disconnect ECM harness connector "E7". (Scheme 39) Turn ignition on. If temperature displayed is -40°F (-40°C), inspect and repair circuits between CTS and ECM for short. See wiring diagram in the «WIRING DIAGRAMS»(ref-21644) 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.

Throttle Position (TP) sensor is a variable resistor that monitors throttle opening. 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. TP sensor open or short circuit.
2. TP 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 WIRING DIAGRAMS article.

1. Connect scan tester to DLC-3. see scheme 1 Turn ignition on. Turn on scan tester. Monitor throttle valve opening percentage. Opening percentage should be about 10 percent with fully closed throttle.
2. Depress accelerator pedal to floor (WOT). Opening percentage should be about 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 TP sensor harness connector. Turn ignition on. Using DVOM, measure voltage between harness connector terminal No. 4 and ground. (Scheme 40) 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 TP sensor component connector terminals No. 1 and 4. Resistance should be 4250-8250 ohms. Measure resistance between terminals No. 1 and 3. Resistance should be 300-6300 ohms with throttle fully closed and 3500-10,300 ohms with throttle fully open.
5. If any resistances measured are NOT within specification, replace TP sensor. See «REMOVE/INSTALL/OVERHAUL»(ref-22181) article. If all resistances measured are within specification, connect TP sensor harness connector.
6. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector "E7", measure voltage between terminals No. 7 (VTA) and No. 22 (E2). (Scheme 39) Voltage should be.3-.8 volt with throttle fully closed and 2.7-5.2 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-21644) article. Repair as needed.
8. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness "E7" connector, measure voltage between terminals No. 1 (VC) and No. 22 (E2). (Scheme 39) Voltage should be 4.5-5.5 volts.
9. If voltage is within specification, inspect VC circuit for open. If voltage is NOT within specification, replace ECM and retest.

Scheme 40

If only Code P0121 is displayed, replace TP sensor 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 at least 25 MPH for at least 2 minutes. Possible causes are

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

Note. Oxygen sensor located nearest radiator is referred to as left oxygen sensor. (Scheme 41)

1. Connect scan tester to DLC-3. see scheme 1 Start vehicle and warm engine to normal operating temperature. Turn on scan tester. Monitor each oxygen sensor in front of converter. Snap accelerate engine 3 times. Sensors should indicate a rich signal (.45 volt or more).
2. If a rich signal is indicated for both sensors, replace ECM and retest. If either sensor does NOT display a rich signal, inspect circuits between ECM and suspect sensor for open or short circuits. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) 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 «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If all circuits are okay, connect scan tester. see scheme 1and (Scheme 41).
2. Start engine, warm to operating temperature. Monitor heated oxygen sensor output voltage and short-term fuel trim. If tester indicates lean (.55 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), see «CODE P0170 - FUEL TRIM MALFUNCTION»(ref-21645-S20268121672001010300000).
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 "E6". Measure voltage between ground and connector "E6" terminals No. 11 (HTR) and No. 10 (HTL) and connector "E5" terminal No. 25 (HTS). (Scheme 39) 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 42)
3. If resistance is 11-16 ohms at 68°F (20°C), inspect circuits between ECM and sensor. See «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If resistance is NOT 11-16 ohms at 68°F (20°C), replace sensor and retest.

Scheme 41

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 «WIRING DIAGRAMS»(ref-21644) 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.

If only Code P0153 is displayed, replace oxygen sensor and retest. If other codes are displayed, diagnose and repair those codes first 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.

Note. Oxygen sensor located nearest radiator is referred to as left oxygen sensor.

1. Inspect all air induction components. Repair as needed. Connect scan tester. see scheme 1and (Scheme 41). 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 - HEATED OXYGEN SENSOR (RIGHT SIDE, NO. 1) CIRCUIT»(ref-21645-S21551849782001010300000).
3. Inspect fuel pressure. See the «BASIC TESTING»(ref-21707) article. Repair as needed. If fuel pressure is okay, inspect fuel injector performance. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed.
4. If all injectors okay, inspect Mass Airflow (MAF) sensor and Coolant Temperature Sensor (CTS). See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed. If both components are okay, inspect ignition system. See «BASIC TESTING»(ref-21707) 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. Mass Airflow (MAF) sensor.
9. Coolant Temperature Sensor (CTS).

1. Inspect spark plugs and ignition system. See «BASIC TESTING»(ref-21707) 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 "E8". Measure voltage between ground terminal No. 34 (E01) and terminals No. 10, 9, 8, 7, 6, 5. (Scheme 39) If voltage is NOT 9-14 volts, go to next step. If voltage is 9-14 volts for each circuit, go to step 4.
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 «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If resistance is NOT 13.4-14.2 ohms, replace injector.
4. Inspect fuel pressure. See «BASIC TESTING»(ref-21707) article. Repair as needed. If fuel pressure is okay, inspect fuel injector performance. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed.
5. If all injectors are okay, inspect EGR system. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Repair as needed. If EGR system is okay, inspect MAF sensor and CTS. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed. If both components are okay, also inspect engine compression, valve clearance and valve timing. See «BASIC TESTING»(ref-21707) article.

See CODE P0300 - RANDOM MISFIRE DETECTED .

See CODE P0300 - RANDOM MISFIRE DETECTED .

Knock Sensors (KS) are located on either side of cylinder block under intake manifold. 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 KS circuit.
2. KS (loose).
3. ECM.

1. Connect scan tester. see scheme 1 Disconnect "EC1" connector. "EC1" connector is a wire-to-wire connector located near the inside rear corner of right cylinder head, under throttle body. Connector is 4-pin type, Dark Gray color.
2. Remove, switch and install terminals No. 1 and 2 from male connector. (Scheme 43) Connect "EC1" connector. Turn ignition on. Clear trouble codes. See «CLEARING TROUBLE CODES»(ref-21645-S01100285462001010300000). Start and warm engine to normal operating temperature.
3. Snap accelerate engine 3 times. Retrieve trouble codes. See «RETRIEVING TROUBLE CODES»(ref-21645-S24654606282001010300000). If same code(s) are repeated as before, go to next step. If code(s) have changed, go to step 5.
4. Inspect circuit(s) between "EC1" connector and ECM harness connector for open or short. Repair as needed. If circuits are okay, replace ECM and retest. Ensure "EC1" male connector terminals are returned to their original position.
5. Inspect circuit(s) between "EC1" connector and knock sensor(s) for open or short. To access harness, intake manifold removal is necessary. See «REMOVE/INSTALL/OVERHAUL»(ref-22181) article. Repair as needed. If harness is okay, replace "KS". Ensure "EC1" male connector terminals are returned to their original position.

Scheme 42

Crankshaft Position (CKP) sensor is a pick-up coil mounted next to crankshaft pulley. 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. Resistance should be 1630-2740 ohms (cold sensor) or 2065-3225 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 «WIRING DIAGRAMS»(ref-21644) 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.

Camshaft Position (CMP) sensor is a pick-up coil mounted in outer corner of left cylinder head, just below rocker arm cover. A one tooth signal plate is mounted to outer 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. Starter.
4. ECM.

1. Disconnect CMP sensor harness connector. Using ohmmeter, measure resistance between sensor connector terminals. Resistance should be 835-1400 ohms (cold sensor) or 1060-1645 ohms (hot sensor).
2. Replace sensor as needed. If sensor is okay, inspect circuits between ECM and CMP sensor for open or short. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) 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.

Exhaust Gas Recirculation (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 below 140°F (60°C).
2. Vehicle under deceleration.
3. Light engine load.
4. Engine racing.

Code is set when EGR gas temperature sensor value does not exceed 72°F (40°C) above ambient air temperature after vehicle is operated for 3 to 5 minutes (50 MPH or more). Possible causes are

1. EGR valve stuck closed.
2. VSV short circuit.
3. EGR gas temperature sensor open circuit.
4. EGR vacuum hose disconnected.
5. 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. Connect scan tester. see scheme 1 Turn ignition on. Read EGR gas temperature. Temperature should be 50°F (10°C). If temperature is within specification, go to step 6. If temperature is NOT within specification, go to next step. If temperature displayed is 37.6°F (3.1°C), there is an open EGR gas temperature sensor circuit.
2. Disconnect EGR gas temperature sensor harness connector. Sensor is mounted in manifold running from EGR valve to throttle body. Connect jumper wire between harness connector terminals.
3. EGR gas temperature displayed should be 318.7°F (159.3°C). If temperature displayed is NOT within specification, go to next step. If temperature displayed is within specification, inspect sensor connectors and terminals. Repair as needed. If connectors are okay, replace sensor and retest.
4. Remove jumper wire. Turn ignition off. Access ECM behind glove box. Connect jumper wire between ECM harness connector "E6" terminal No. 14 (THG) and connector "E7" terminal No. 22 (E2). (Scheme 39) Turn ignition on. EGR gas temperature displayed should be 318.7°F (159.3°C).
5. If temperature displayed is within specification, inspect and repair open in circuits between ECM and EGR gas temperature sensor. If temperature displayed is NOT within specification, replace ECM and retest.
6. Inspect vacuum hoses. Repair as needed. If all hoses are okay, inspect VSV. On scan tester, select active test mode. Check operation of VSV when activated by scan tester. VSV is located under intake plenum cover.
7. Start and run engine. With system in OFF mode, air should exhaust from small filter on end of valve. (Scheme 44) With system in ON mode, air should pass through valve. If valve operates correctly, go to step 11. If valve does NOT operate correctly, go to next step.
8. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 26-46 ohms at 68°F (20°C). Measure resistance between each terminal and body of valve. Resistance should be infinite. Replace EGR VSV as needed.
9. Check VSV operation. Apply battery voltage to VSV terminals. Air should exhaust from small filter on end of valve. (Scheme 44) Remove battery voltage from valve terminals. Air should pass through VSV. Replace as needed.
10. If valve meets all specifications in steps 8 and 9, inspect circuits between EGR VSV and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.
11. Inspect EGR vacuum modulator. See procedures in «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed. Inspect EGR valve. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed.
12. Ensure all components are connected. Inspect EGR gas temperature sensor. Start and run engine. Select active test mode on scan tester (EGR system ON). Run engine at 4000 RPM for 3 minutes. Monitor EGR gas temperature. Temperature should be 284°F (140°C) or more.
13. If temperature is NOT within specification, replace sensor. If temperature is within specification, replace ECM and retest.

Scheme 43

Diagnosis & Repair (OBD-II Scan Tester ONLY)

1. Disconnect EGR gas temperature sensor. Sensor is located on manifold between EGR valve and throttle body. Using ohmmeter, measure resistance between sensor terminals. If resistance is 600,000 ohms or less, go to next step. If resistance is NOT 600,000 ohms or less, inspect sensor. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed.
2. Turn ignition on. Using DVOM, measure voltage between sensor harness connector terminals. If voltage is 4.5-5.5 volts, go to step 4. If voltage is NOT 4.4-5.5 volts, go to next step.
3. Access ECM behind glove box. Using DVOM, backprobe harness connector. Measure voltage between ECM connector "E6" terminal No. 14 (THG) and connector "E7" terminal No. 22 (E2). (Scheme 39) If voltage is 4.5-5.5 volts, inspect circuits between EGR gas temperature sensor and ECM for open. See «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If voltage is NOT 4.4-5.5 volts, replace ECM and retest.
4. Inspect all EGR system vacuum hoses. Replace as needed. Check operation of EGR Vacuum Switching Valve (VSV). Access ECM behind glove box. Ensure ignition is off. Disconnect ECM harness connector "E6". Turn ignition on. Using jumper wire, connect ECM connector "E6" terminal No. 12 (EGR) to ground.
5. VSV is located under intake plenum cover. With jumper wire connected, VSV is on. Air should exhaust through filter on end of valve. (Scheme 44) Disconnect jumper wire. Air should pass through valve. If valve operates correctly, go to step 9.
6. If valve does operate correctly, turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 26-46 ohms at 68°F (20°C). Measure resistance between each terminal and body of valve. Resistance should be infinite. Replace VSV as needed.
7. Check VSV operation. Apply battery voltage to valve terminals. Air should exhaust from small filter on end of valve. (Scheme 44) Remove battery voltage from valve terminals. Air should pass through valve. Replace as needed.
8. If valve meets all specifications in steps 6 and 7, inspect circuits between EGR VSV and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.
9. Inspect EGR vacuum modulator. See procedures in «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed. Inspect EGR valve. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed.
10. Inspect EGR gas temperature sensor. Start and run engine. Select active test mode on scan tester (EGR system ON). Run engine at 4000 RPM for 3 minutes. Monitor EGR gas temperature. Temperature should be 284°F (140°C) or more.
11. If temperature is NOT within specification, replace sensor. If temperature is within specification, replace ECM and retest.

See CODE P0401 - INSUFFICIENT EXHAUST GAS RECIRCULATION FLOW DETECTED . Code is set when Exhaust Gas Recirculation (EGR) gas temperature sensor value is high. Engine not yet at normal operating temperature. Possible causes are

1. EGR valve stuck open.
2. EGR Vacuum Switching Valve (VSV).
3. EGR VSV open circuit.
4. EGR gas temperature sensor short circuit.
5. 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. Connect scan tester. see scheme 1 Turn ignition on. Read EGR gas temperature. Temperature should be 302°F (150°C). If temperature is within specification, go to step 6. If temperature is NOT within specification, go to next step. If temperature displayed is 318.7°F (159.3°C), there is a short in EGR gas temperature sensor circuit.
2. Disconnect EGR gas temperature sensor harness connector. Sensor is mounted in manifold running from EGR valve to throttle body.
3. EGR gas temperature displayed should be 37.6°F (3.1°C). If temperature displayed is NOT within specification, go to next step. If temperature displayed is within specification, replace sensor and retest.
4. Turn ignition off. Access ECM behind glove box. Disconnect ECM harness connector "E6". (Scheme 39) Turn ignition on. EGR gas temperature displayed should be 37.6°F (3.1°C).
5. If temperature displayed is within specification, inspect and repair open in circuits between ECM and EGR gas temperature sensor. If temperature displayed is NOT within specification, replace ECM and retest.
6. Inspect VSV. On scan tester, select active test mode. Check operation of VSV when activated by scan tester. VSV is located under intake plenum cover.
7. Start and run engine. With system in OFF mode, air should exhaust from small filter on end of VSV. (Scheme 44) With system in ON mode, air should pass through valve. If valve does NOT operate correctly, go to next step. If VSV operates correctly, check EGR valve for sticking and heavy carbon deposits. If problem is found, replace EGR valve.
8. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 26-46 ohms at 68°F (20°C). Measure resistance between each terminal and body of valve. Resistance should be infinite. Replace VSV as needed.
9. Check VSV operation. Apply battery voltage to valve terminals. Air should exhaust from small filter on end of valve. (Scheme 44) Remove battery voltage from valve terminals. Air should pass through valve. Replace as needed.
10. If valve meets all specifications in steps 8 and 9, inspect circuits for short between EGR VSV and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.

1. Disconnect EGR gas temperature sensor. Sensor is located on manifold between EGR valve and throttle body. Using ohmmeter, measure resistance between sensor terminals. If resistance is about 2500 ohms or less, go to next step. If resistance is NOT about 2500 ohms or less, replace sensor.
2. Inspect circuits between EGR gas temperature sensor and ECM for short. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuits are okay, go to next step.
3. Check operation of EGR Vacuum Switching Valve (VSV). VSV located under intake plenum cover. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace valve as needed. If valve is okay, inspect EGR valve. Replace as needed.
4. Inspect circuits for short between EGR VSV and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuits are 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 20-50 MPH. Possible causes are

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

Note. Oxygen sensor located nearest radiator is referred to as left oxygen sensor. (Scheme 41)

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-21645-S24654606282001010300000).
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 - HEATED OXYGEN SENSOR (RIGHT SIDE, NO. 1) CIRCUIT»(ref-21645-S21551849782001010300000). Repair systems as needed. If oxygen sensor circuits and sensors are okay, replace catalytic converter and retest.

The ECM changes duty signal to EVAP Vacuum Switching Valve (VSV) so that intake quantity of HC emissions is appropriate for driving conditions (engine load, engine speed, etc.) after engine is at normal operating temperature. Code is set when proper response to computer command does not occur. Possible causes are

1. VSV open or short circuit.
2. EVAP VSV.
3. ECM.
4. Vacuum hose blocked or disconnected.
5. Charcoal canister.

1. Connect scan tester. see scheme 1 Turn on ignition and scan tester. Access EVAP VSV. VSV is under plenum cover. Select active test mode on scan tester. Air should pass through valve when on. Air should NOT pass through valve when off.
2. If valve operates correctly, go to step 5. If valve does NOT operate correctly, turn ignition off. Disconnect VSV harness connector. Using ohmmeter, measure resistance between valve terminals. Resistance should be 27-33 ohms at 68°F (20°C). Measure resistance between each valve terminal and valve body. Resistance should be infinite. Replace valve as needed.
3. Connect battery voltage to valve connector terminals. Air should flow through valve. Remove battery voltage. Air should NOT flow through valve. Replace valve as needed.
4. If valve operates correctly, inspect circuit for open or short between EFI relay and ECM. See «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuit is okay, replace ECM.
5. Inspect vacuum hose connection. Repair as needed. If vacuum lines are okay, inspect charcoal canister. See procedures in «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed.

1. Disconnect EVAP VSV harness connector. VSV is located under plenum cover. Using ohmmeter, measure resistance between valve terminals. Resistance should be 27-33 ohms at 68°F (20°C). Measure resistance between each valve terminal and valve body. Resistance should be infinite. Replace valve as needed.
2. Connect battery voltage to valve connector terminals. Air should flow through valve. Remove battery voltage. Air should NOT flow through valve. Replace valve as needed.
3. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM harness connector. Measure voltage between EVP1 and ground. If 9-14 volts is present, go to next step. If 9-14 volts is NOT present, inspect and repair circuit. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article.
4. Inspect EVAP vacuum hose connections. Repair as needed. Inspect charcoal canister. See «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed. If canister is okay, replace ECM and retest.

Vehicle Speed Sensor (VSS), driven by the differential, outputs a signal to combination meter. 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. VSS open or short circuit.
2. VSS failure.
3. Combination meter.
4. ECM.

1. Test drive vehicle and check operation of speedometer. If speedometer is not functioning correctly, see «INSTRUMENT PANEL»(ref-33953) article in ACCESSORIES/SAFETY EQUIPMENT. If speedometer is functioning correctly, go to next test.
2. Access ECM behind glove box. Ensure ignition is off. Disconnect ECM connector "E5". (Scheme 39) Using ohmmeter, check continuity between terminal No. 12 (SP1) and ground. If continuity exists, inspect and repair short in circuit. If continuity does NOT exist, go to next step.
3. Turn ignition on. Using DVOM, measure voltage between ECM harness connector "E5", terminal No. 12 (SP1) and ground. If voltage is 9-14 volts, go to next step. If voltage measured is NOT 9-14 volts, inspect for open in circuit. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.
4. Inspect for possible open circuit between combination meter and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuit is okay, replace ECM and retest.

The ECM operates only Idle Air Control (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. IAC valve stuck or closed.
2. IAC valve circuit open or short.
3. VSV for A/C idle-up.
4. Air intake leak.

Repair & Diagnosis

1. Inspect air induction system for leaks. Repair as needed. Inspect VSV for A/C idle-up. See the «SYSTEM/COMPONENT TESTS»(ref-21595) article. Repair as needed.
2. Ensure ignition if off. Access ECM behind glove box. Disconnect ECM harness connector E8. Turn ignition on. Using DVOM, measure voltage between individual connector terminals RSO, RSC, and ground. (Scheme 39) 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 45)
4. For resistance specifications, see «IAC RESISTANCE»(ref-21645-S04074560952004041500000) 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 Terminal No. Ohms Cold (1) 1 & 2 17.0-24.5 2 & 3 17.0-24.5 Hot (2) 1 & 2 21.5-28.5 2 & 3 21.5-28.5 (1) 14-122°F (-10-50°C). (2) 122-212°F (50-100°C).
5. Inspect operation of IAC valve. Remove valve. To inspect valve, see «SYSTEM/COMPONENT TESTS»(ref-21595) article. Replace as needed. If valve is okay, replace ECM and retest.

Scheme 44

Built into Throttle Position (TP) sensor, 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 (CTP) switch open circuit.
2. CTP switch.
3. ECM.

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

1. Connect scan tester. see scheme 1 Disconnect TP sensor harness connector. Using jumper wire, connect wire to TP sensor harness connector terminals No. 1 and 2. (Scheme 40)
2. Turn ignition on. Read CTP switch signal on scan tester. If CTP switch signal displayed is ON, replace TP sensor and retest. If signal displayed is OFF, go to next step.
3. Turn ignition is off. Remove jumper wire. Access ECM behind glove box. Connect jumper wire between ECM connector "E8" terminals No. 32 (IDL) and connector "E7" terminal No. 22 "E2". (Scheme 39) Turn ignition on. Read CTP switch signal on scan tester. If CTP switch signal displayed is ON, inspect circuits between TP sensor and ECM. Repair as needed. If signal displayed is OFF, replace ECM and retest.

1. Ensure ignition is off. Disconnect TP sensor harness connector. Turn ignition on. Using DVOM, measure voltage between terminals No. 1 and 2. (Scheme 40) 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 TP sensor 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 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. Ensure ignition is off. Disconnect ignitor 4-pin connector. Ignitor is in back of air cleaner housing. Turn ignition on. Using DVOM, measure voltage between terminal No. 2 of harness connector and ground. (Scheme 46)
2. If voltage is 9-14 volts, go to next step. If voltage is NOT 9-14 volts, inspect power supply circuit to ignitor. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.
3. Turn ignition off. Disconnect 12-pin connector from ignitor. Turn ignition on. Measure voltage between harness connector terminals No. 4-6 and 10-12, and ground. (Scheme 46) Voltage for all individual circuits should be 9-14 volts.
4. If voltage for all circuits are within specification, go to step 6. If voltage for any circuit is NOT 9-14 volts, turn ignition off. Disconnect harness connector of suspect ignition coil connected to faulty ignitor circuit. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article.
5. Measure resistance between suspect coil terminals. Resistance should be.54-.84 ohms for cold coil and.68-.98 ohms for hot coil. If resistances measured are NOT within specifications, replace coil. If resistances are within specification, inspect circuit(s) between coil and ignitor for shorts or opens. Repair as needed.
6. Turn ignition off. Using ohmmeter, check continuity between ignitor 4-pin harness connector terminal No. 4 and ground. (Scheme 46) If continuity exists, go to next step. If continuity does NOT exist, repair circuit and retest.
7. Turn ignition on. Measure voltage between terminal No. 3 and ground. If voltage is 4.5-5.5 volts, go to next step. If voltage is NOT 4.5-5.5 volts, inspect IGF circuit between ECM and ignitor for open or short. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed. If circuit is okay, replace ECM and retest.
8. Inspect IGT1-IGT6 circuits between ignitor and ECM for opens or shorts. Repair as needed. If all circuits are okay, turn ignition on. Measure voltage between terminals No. 15, 16, 24, 26, 29 and 30 (IGT1-IGT6) of ECM connector, and ground while cranking engine.
9. Voltage should be.5-1.0 volts for each circuit. If voltage for all circuits are within specification, replace ignitor and retest. If voltage for any circuit is NOT within specification, replace ECM and retest.

Scheme 45

See CODE P0335 - CRANKSHAFT POSITION SENSOR CIRCUIT . Code is set when ECM receives no Crankshaft Position (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 SENSOR 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 «WIRING DIAGRAMS»(ref-21644) 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 «WIRING DIAGRAMS»(ref-21644) 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 behind glove box. Using DVOM, measure voltage between terminal No. 14 (BATT) of ECM connector "E5" and ground. (Scheme 39) 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 (15-amp). EFI fuse is located in engine compartment fuse box. Replace as needed. If fuse okay, inspect circuit between EFI fuse (15-amp) and ECM. See wiring diagram in «WIRING DIAGRAMS»(ref-21644) article. Repair as needed.

See CODES P0325 & P0330 - KNOCK SENSOR NO. 1 & 2 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 Park/Neutral Position (PNP) switch sends a signal to ECM when transaxle 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).

Possible causes are

1. PNP switch short circuit.
2. PNP switch.
3. ECM.

1. Disconnect PNP switch harness connector. PNP switch is located at transaxle where shifter select cable is mounted. Using ohmmeter, check continuity of switch terminals in specified positions. (Scheme 47)and see scheme 14. Replace as needed.
2. If switch is okay, access ECM behind glove box. Turn ignition on. Using DVOM, measure voltage between ECM harness connector "E8" terminal No. 14 (NSW) and ground. (Scheme 39)
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 within specification, replace ECM and retest.
4. If any voltages measured are NOT within specification, inspect circuit between PNP switch and ECM for open or short. Repair as needed.

Scheme 46

Scheme 47