DTC P0133: Heated Oxygen Sensor (front) Circuit Slow Responce

CIRCUIT OPERATION

A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 38) from the output terminal (terminal No. 3) of the heated oxygen sensor (front).
Terminal No. 4 of the heated oxygen sensor (front) is grounded with ECM (terminal No. 39).
The ECM applies an offset voltage of 0.5 volt to terminal No. 4 of the heated oxygen sensor (front).

TECHNICAL DESCRIPTION

The heated oxygen sensor (front) detects the concentration of oxygen in the exhaust gas; it converts those data to voltage, and inputs the resulting signals to the ECM.
When the heated oxygen sensor (front) begins to deteriorate, the heated oxygen sensor signal response becomes poor.
The ECM checks for the heated oxygen sensor (front) rich/lean switching frequency.

DESCRIPTIONS OF MONITOR METHODS

MONITOR EXECUTION

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)

Heated oxygen sensor (front) heater monitor
Misfire monitor
Fuel system monitor
Heated oxygen sensor (rear) feedback control system monitor

Sensor (The sensor below is determined to be normal)

Mass airflow sensor
Engine coolant temperature sensor
Intake air temperature sensor
Barometric pressure sensor
Throttle position sensor
Accelerator pedal position sensor

DTC SET CONDITIONS

Logic Flow Chart

Check Conditions

Engine coolant temperature is higher than 60°C (140°F).
Engine speed is between 1,406 and 3,500 r/min.
Volumetric efficiency is between 20 and 65 percent.
Under the closed loop air/fuel control.
The accelerator pedal is depressed.
Short-term fuel trim is between -20 and +17 percent.
More than 3.5 seconds have elapsed after the above mentioned conditions have been met.
During the drive cycle, the ECM performs monitoring with the accumulated total time of 10 seconds, 5 times.

Judgement Criteria

The average of the heated oxygen sensor (front) rich/lean switching frequency is less than 9 times <M/T> or 8 times <TC-SST> for the accumulated time of 10 seconds.
The heated oxygen sensor (front) rich/lean switching frequency is less than 20 times <M/T> or 16 times <TC-SST> for the accumulated time of 10 seconds.

note

If the sensor switching frequency is lower than the Judgement Criteria due to the M.U.T.-III OBD-II test Mode - HO2S Test Results, it is assumed that the heated oxygen sensor has deteriorated. If it is higher, it is assumed that the harness is damaged or has a short circuit.
If the heated oxygen sensor signal voltage has not changed even once (lean/rich) after the DTC was erased, the sensor switch time will display as 0 second.

FAIL-SAFE AND BACKUP FUNCTION

None

OBD-II DRIVE CYCLE PATTERN

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

Heated oxygen sensor (front) deteriorated.
Connector damage.
ECM failed.

DIAGNOSIS

Required Special Tools:

MB991958: Scan Tool (M.U.T.-III Sub Assembly)

MB991824: V.C.I.
MB991827: USB Cable
MB991910: Main Harness A

MB991658: Test Harness

STEP 1. Using scan tool MB991958, check data list item AC: Heated Oxygen Sensor (front).

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 AC, Heated Oxygen Sensor (front).
(4)Warm up the engine, 2,500 r/min.

Output voltage repeats 0.4 volt or less and 0.6 to 1.0 volt 9 times <M/T> or 8 times <TC-SST> or more within 10 seconds.

(5)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.

STEP 2. Check the heated oxygen sensor (front).

(1)Disconnect the heated oxygen sensor (front) connector C-34 and connect test harness special tool MB991658 to the connector on the heated oxygen sensor (front) side.

(2)Warm up the engine until engine coolant temperature reaches 80°C (176°F) or higher.

(3)Rev the engine for 5 minutes or more with the engine speed of 2,000 r/min.

(4)Connect a digital voltage meter between terminal No. 3 and terminal No. 4.
(5)Warm up the engine, 2,500 r/min

Output voltage repeats 0.4 volt or less and 0.6 to 1.0 volt 9 times <M/T> or 8 times <TC-SST> or more within 10 seconds.

caution

Be very careful when connecting the jumper wires; incorrect connection can damage the heated oxygen sensor.
Be careful the heater can be damaged if a voltage beyond 8 volts is applied to the heated oxygen sensor heater.

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. Therefore, if the output voltage is low, use a jumper wire to connect the terminal No. 1 and the terminal No. 2 of the heated oxygen sensor with the positive terminal and the negative terminal of 8 volts power supply respectively, then check again.

Q. Is the sensor operating properly?

Go to Step 3.

Replace the heated oxygen sensor (front). Then go to Step 4.

STEP 3. Check harness connector C-34 at heated oxygen sensor (front) and harness connector B-09 at ECM for damage.

Q. Is the harness connector in good condition?

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 4.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 4.

STEP 4. Test the OBD-II drive cycle.

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

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0133 set?

	Retry the troubleshooting.

	The inspection is complete.