Note. For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.
| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article. |
Note. Bank No. 1 refers to bank which includes cylinder No. 1. Bank No. 2 refers to bank without cylinder No. 1. Heated oxygen sensor No. 1 refers to sensor closest to engine block. Heated oxygen sensor No. 2 refers to sensor farthest away from engine block.
Circuit Description
The ECM compares waveform of oxygen sensor located in front of catalytic converter with waveform of oxygen sensor located behind catalytic converter to determine if catalytic converter performance has deteriorated. If catalytic converter is functioning properly, waveform of oxygen sensor after catalytic converter will switch back and forth between rich and lean much more slowly than waveform of oxygen sensor in front of catalytic converter. (Scheme 113)
DTC is set if after driving vehicle for specified period of time and speed and engine is at normal operating temperature, oxygen sensor waveforms are the same. DTC P0420 is for bank No. 1. DTC P0430 is for bank No. 2. Possible causes are
- Exhaust gas system leak.
- Faulty oxygen sensor.
- Faulty catalytic converter.
Scheme 113
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.
Scheme 114
Scheme 115
- Connect hand-held tester to DLC3, or connect probe of oscilloscope between terminals OXL1, OXL2, OXR1, OXR2 and E1 of ECM connectors. Start engine and warm it up with all the accessories off until engine coolant temperature is stable.
- Race engine at 2500-3000 RPM for about 3 minutes. After confirming that waveforms of heated oxygen sensor (bank 1, 2 sensor 1 (OXL1, OXR1 )), waveforms around 0.5 volts during feedback to ECM, check waveform of heated oxygen sensor (bank 1, 2 sensor 2 (OXL2, OXR2)). (Scheme 114)
- If there is a malfunction in the system, the waveform of heated oxygen sensor (bank 1, 2 sensor 2 (OXL2, OXR2)) is almost the same as that of heated oxygen sensor (bank 1, 2 sensor 1 (OXL1, OXR1)) on the left. (Scheme 115) There are some cases where, even though a malfunction exists, MIL may light up or not light up.
Scheme 116
- Retrieve trouble codes. See «RETRIEVING DIAGNOSTIC TROUBLE CODES»(ref-151781-S29975222372003010800000) under SELF-DIAGNOSTIC SYSTEM. If only DTC P0420 or P0430 is displayed, go to next step. If other codes are displayed, diagnose and repair those codes first and retest.
- Check for exhaust leaks. Repair as necessary. If exhaust system is okay, check heated oxygen sensor circuits. See «DTC P0130, DTC P0150, DTC P2195, DTC P2196, DTC P2197 OR DTC P2198»(ref-151781-S34200046912003010800000) test. Repair as necessary. If no problems are indicated, go to next step.
- Check heated oxygen sensor. Disconnect the H9, H10, H15 and H16 heated oxygen sensor connectors. Measure the resistance between the terminals of the connectors (component side). (Scheme 116) See «HEATED OXYGEN SENSOR RESISTANCE»(ref-151781-S20823466142003022600000) table. Replace appropriate oxygen sensor as necessary. If oxygen sensor circuits are okay, replace appropriate catalytic converter and retest. HEATED OXYGEN SENSOR RESISTANCE Terminal No. °F (°C) Ohms Bank 1 Sensor 1 & Bank 2 Sensor 1 1-4 68 (20) 11-16 1-4 1472 (800) 23-32 Bank 1 Sensor 2 & Bank 2 Sensor 2 2-3 68 (20) 11-16 2-3 1472 (800) 23-32