DTC P0143: Heated Oxygen Sensor (3rd) Circuit Low Voltage <California>

CIRCUIT OPERATION

• A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 54) from the output terminal (terminal No. 3) of the heated oxygen sensor (3rd).
  
• Terminal No. 4 of the heated oxygen sensor (3rd) is grounded with ECM (terminal No. 55).
  
• The ECM applies an offset voltage of 0.5 volt to terminal No. 4 of the heated oxygen sensor (3rd).
  

TECHNICAL DESCRIPTION

• The ECM checks for the heated oxygen sensor (3rd) output voltage.
  

DESCRIPTIONS OF MONITOR METHODS

Heated oxygen sensor (3rd) output voltage is under the specified range.

MONITOR EXECUTION

Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

• Heated oxygen sensor (front) monitor
  
• Heated oxygen sensor heater (front) monitor
  
• Heated oxygen sensor inactive (front) monitor
  
• Heated oxygen sensor offset voltage monitor
  
• Air/fuel ratio feedback monitor
  
• Heated oxygen sensor heater (3rd) monitor
  

• Mass airflow sensor
  
• Engine coolant temperature sensor
  
• Intake air temperature sensor
  
• Barometric pressure sensor
  

DTC SET CONDITIONS

• Heated oxygen sensor offset voltage is between 0.4 and 0.6 volt.
  
• Battery positive voltage is between 11 and 16.5 volts.
  
• 3 minutes or more have passed since the engine starting sequence was completed.
  

• Heated oxygen sensor (3rd) output voltage is lower than 0.2 volt for 2 seconds.
  

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 22 .

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

• Heated oxygen sensor (3rd) failed.
  
• Open or shorted circuit in heated oxygen sensor (3rd) output line or harness damage.
  
• Open circuit in heated oxygen sensor (3rd) ground line or harness damage.
  
• Connector damage.
  
• ECM failed.
  

caution To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. (1)Connect scan tool MB991958 to the data link connector. (2)Start the engine and run at idle. (3)Set scan tool MB991958 to the data reading mode for item B1, Heated Oxygen Sensor (3rd). Transaxle: 2nd speed (CVT: "L" range) Drive with wide open throttle Engine: 3,500 r/min The output voltages should be between 0.6 and 1.0 volt. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the sensor operating properly? It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions . Go to Step 2.

(3)Measure the voltage between terminal No. 3 and ground by backprobing under the following driving. Transaxle: 2nd speed (CVT: "L" range) Drive with wide open throttle Engine: 3,500 r/min or more The output voltage should be between 1.0 and 1.5 volts. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage within the specified range? Go to Step 3. Go to Step 8.

	Go to Step 4.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors. (2)Start the engine and run at idle.

(3)Measure the voltage between terminal No. 54 and ground under the following driving. Transaxle: 2nd speed (CVT: "L" range) Drive with wide open throttle Engine: 3,500 r/min or more The output voltage should be between 1.0 and 1.5 volts. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage between 1.0 and 1.5 volts? Go to Step 5. Go to Step 7.

	Go to Step 6.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

(1)Start the engine and run at idle. (2)Set scan tool MB991958 to the data reading mode for item B1, Heated Oxygen Sensor (3rd). Transaxle: 2nd speed (CVT: "L" range) Drive with wide open throttle Engine: 3,500 r/min or more The output voltage should be between 0.6 and 1.0 volt. (3)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the sensor operating properly? It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions . Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 14.

Check harness connector A-10 and C-37 at intermediate connector for damage, and repair or replace as required. Refer to GROUP 00E, Harness Connector Inspection . If intermediate connector is in good condition, repair harness wire between heated oxygen sensor (3rd) connector D-31 (terminal No. 3) and ECM connector B-108 (terminal No. 54) because of open circuit or harness damage. Then go to Step 14.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 9.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 10.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors. (2)Turn the ignition switch to the "ON" position.

(3)Measure the voltage between terminal No. 55 and ground. Voltage should be between 0.4 and 0.6 volt. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage between 0.4 and 0.6 volt? Go to Step 11. Check harness connector A-10 and C-37 at intermediate connector for damage, and repair or replace as required. Refer to GROUP 00E, Harness Connector Inspection . If intermediate connector is in good condition, repair harness wire between headed oxygen sensor (3rd) connector D-31 (terminal No. 4) and ECM connector B-108 (terminal No. 55) because of open circuit or harness damage. Then go to Step 14.

note Check harness after checking intermediate connector A-10 and C-37. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 12.

	Repair it. Then go to Step 14.

note Check harness after checking intermediate connector A-10 and C-37. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 13.

	Repair it. Then go to Step 14.

(4)Connect a digital voltage meter between terminal No. 3 and terminal No. 4. (5)Measure the output voltage of heated oxygen sensor under the following driving. Transaxle: 2nd speed (CVT: "L" range) Drive with wide open throttle Engine: 3,500 r/min or more Standard value: 0.6 - 1.0 V note If the temperature of sensing area does not reach the high temperature [of approximately 400°C (752°F) or more] even though the heated oxygen sensor is normal, the output voltage would be possibly low in spite of the rich air-fuel ratio. note When the vehicle is driven with high loads, the temperature of the sensing area of the heated oxygen sensor is sufficiently high. Thus, it is not necessary to apply the voltage to the heater. Q. Is the measured voltage between 0.6 and 1.0 volt? Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 14. Replace the heated oxygen sensor (3rd). Then go to Step 14.

(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 22 .

	Retry the troubleshooting.

	The inspection is complete.