2006 Mitsubishi Lancer L4-2.0L SOHC Copyright © 2013, ALLDATA 10.

52SS Page 1

A L L Diagnostic Trouble Codes ( DTC ): P Code Charts

P0031
DTC P0031: Heated Oxygen Sensor Heater Control Circuit Low (sensor 1)

Heated Oxygen Sensor (Front) Heater Circuit Part 1

Heated Oxygen Sensor (Front) Heater Circuit Part 2

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CIRCUIT OPERATION
- Power is supplied from the MFI relay (terminal No. 4) to the heated oxygen sensor (front) heater.
- The ECM <M/T> or PCM <A/T> (terminal No. 3) controls continuity to the heated oxygen sensor (front) heater by turning the power transistor in
the ECM <M/T> or PCM <A/T> "ON" and "OFF".

TECHNICAL DESCRIPTION
- The ECM <M/T> or PCM <A/T> checks whether he heater current is within a specified range when the heater is energized.
- The ECM <M/T> or PCM <A/T> checks whether the heater voltage is within a specified range when the heater is energized.

DESCRIPTIONS OF MONITOR METHODS

- The heated oxygen sensor heater (front) current or voltage is out of specified range.

MONITOR EXECUTION
- Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Not applicable

Sensor (The sensor below is determined to be normal)

- Engine coolant temperature sensor

DTC SET CONDITIONS

Logic Flow Chart

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Logic Flow Chart

Check Conditions
- More than 2 seconds have passed since the engine starting sequence was completed.
- While the heated oxygen sensor (front) heater is on.
- Battery positive voltage is between 11 and 16.5volts.

Judgement Criterion
- The heated oxygen sensor (front) heater current has continued to be lower than 0.17 ampere for 2 seconds.

Check Conditions
- More than 2 seconds have passed since the engine starting sequence was completed.
- While the heated oxygen sensor (front) heater is off.
- Battery positive voltage is between 11 and 16.5 volts.

Judgement Criterion
- The heated oxygen sensor (front) heater voltage has continued to be lower than 2.0 volts for 2 seconds.

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle Pattern 2. See: Powertrain Management/Computers and Control Systems/Testing and
Inspection/Monitors, Trips, Drive Cycles and Readiness Codes/OBD-II Drive Cycle Pattern Lists

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
- Open or shorted heated oxygen sensor (front) heater circuit, harness damage or connector damage.
- Open circuit in heated oxygen sensor (front) heater failed.
- ECM failed. <M/T>
- PCM failed. <A/T>

DIAGNOSIS

Required Special Tool:

- MD998464: Test Harness

STEP 1. Check connector B-113 at the heated oxygen sensor (front) for damage.

Q: Is the connector in good condition?

YES: Go to Step 2.

NO: Repair or replace it. Then go to Step 12.

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

2006 Mitsubishi Lancer L4-2.0L SOHC Copyright © 2013, ALLDATA 10.52SS Page 4

1. Disconnect heated oxygen sensor (front) connector B-113 and connect test harness special tool, MD998464, to the connector on the heated oxygen
(front) sensor side.

2. Measure the resistance between heated oxygen sensor connector terminal No. 1 (red clip) and terminal No. 3 (blue clip).

Standard value: 4.5 - 8.0 Ohms [at 20 degrees C (68 degrees F)]

Q: Is the measured resistance between 4.5 and 8.0 Ohms [at 20 degrees C (68 degrees F)]?

YES: Go to Step 3

NO: Replace the heated oxygen sensor (front). Then go to Step 12.

STEP 3. Measure the power supply voltage at heated oxygen sensor (front) harness side connector B-113.

1. Disconnect connector B-113 and measure at the harness side.

2. Turn the ignition switch to the "ON" position.
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3. Measure the voltage between terminal No. 1 and ground.

- Voltage should be battery positive voltage

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is battery positive voltage (approximately 12 volts) present?

YES: Go to Step 5.

NO: Go to Step 4.

STEP 4. Check harness connector B-12X at the MFI relay for damage.

Q: Is the harness connector in good condition?

YES: Repair harness wire between MFI relay connector B- 12X (terminal No. 4) and heated oxygen sensor (front) connector B-113 (terminal No.
1) because of open circuit or short circuit to ground. Then go to Step 12.

NO: Repair or replace it. Then go to Step 12.

STEP 5. Measure the power supply voltage at ECM connector C-119 <M/T> or PCM connector C-120 <A/T> by backprobing.
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1. Do not disconnect connector C-119 <M/T> or C-120 <A/T>.

2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No. 3 and ground by backprobing.

- Voltage should be battery positive voltage.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is battery positive voltage (approximately 12 volts) present?

YES: Go to Step 8.

NO: Go to Step 6.
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STEP 6. Check harness connector C-119 at ECM <M/T> or harness connector C-120 at PCM <A/T> for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 7.

NO: Repair or replace it. Then go to Step 12.

STEP 7. Check for open circuit and short circuit to ground between heated oxygen sensor (front) connector B-113 (terminal No. 3) and ECM
connector C-119 <M/T> or PCM connector C-120 <A/T> (terminal No. 3).

Q: Is the harness wire in good condition?

YES: Replace the ECM or the PCM. Then go to Step 12.

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NO: Repair it. Then go to Step 12.

STEP 8. Check harness connector C-119 at ECM <M/T> or harness connector C-120 at PCM <A/T> for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 9.

NO: Repair or replace it. Then go to Step 12.

STEP 9. Check for harness damage between MFI relay connector B-12X (terminal No. 4) and heated oxygen sensor (front) connector B-113
(terminal No. 1).

Q: Is the harness wire in good condition?

2006 Mitsubishi Lancer L4-2.0L SOHC Copyright © 2013, ALLDATA 10.52SS Page 9

YES: Go to Step 10.

NO: Repair it. Then go to Step 12.

STEP 10. Check for harness damage between heated oxygen sensor (front) connector B-113 (terminal No. 3) and ECM connector C-119 <M/T>
or PCM connector C-120 <A/ T> (terminal No. 3).

Q: Is the harness wire in good condition?

YES: Go to Step 11.

NO: Repair it. Then go to Step 12.

STEP 11. Check the trouble symptoms.

1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 See: Powertrain
Management/Computers and Control Systems/Testing and Inspection/Monitors, Trips, Drive Cycles and Readiness Codes/OBD-II Drive Cycle
Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q:Is DTC P0031 set?

YES: Replace the ECM or the PCM. Then go to Step 12.

NO: It can be assumed that this malfunction is intermittent.

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STEP 12. 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 2 See: Powertrain
Management/Computers and Control Systems/Testing and Inspection/Monitors, Trips, Drive Cycles and Readiness Codes/OBD-II Drive Cycle
Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0031 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.