After the vehicle started, ECM works in open-loop mode, in which ECM ignores the Pre-Catalytic oxygen sensor signal voltage when
calculating the Air-Fuel ratio. ECM provides an approximate 450mV reference voltage to the Pre-Catalytic oxygen sensor. When
the engine is running, Pre-Catalytic oxygen sensors start heating and begin to generate a 0-0.1 V voltage, which fluctuates. Once
ECM detects that the Pre-Catalytic oxygen sensor voltage exceeds a preset threshold voltage, ECM immediately enters into the
closed-loop mode. ECM uses Pre-Catalytic oxygen sensor signal voltage to determine the Air-Fuel ratio. If the Pre-Catalytic oxygen
sensor voltage is increased to above the reference voltage (tend to 1 V), the mixture is too rich. If the Pre-Catalytic oxygen sensor
the voltage decreased to below the reference voltage (tend to 0 mV), the mixture is too lean.
ECM  provides  a  signal  through  ECM  harness  connector  EO01  terminal  No.10  to  Pre-Catalytic  oxygen  sensor  wiring  harness
connector EO02 terminal B and an internal low reference voltage through ECM harness connector EO01 terminal No.2 to Pre-
Catalytic oxygen sensor wiring harness connector EO02 terminal No. A.

2. Conditions For Setting DTC and The Fault Location:

DTC

Code

DTC Detection Strategy

Conditions For Setting The DTC (Control Strategy)

Fault Locations

P0131

1. Pre-Catalytic Oxygen Sensor

Voltage Too High

2. Pre-Catalytic Oxygen Sensor

Voltage Too Low

1. Engine Running Longer Than 60 s.

2. Coolant Temperature Less Than 70°C (158 ºF).

3. Oxygen sensor signal is 0.

4. Duration Longer Than 25 s.

1. Sensor Circuit

2. Sensor

3. ECM

P0132

1. Engine Running Longer Than 60 s.

2. Coolant temperature is less than 70°C (158 ºF).

3. Pre-Catalytic oxygen sensor signal is short to power

supply, oxygen sensor signal is around 3,200 mV.

4. Duration Longer Than 25 s.

P0133

1. Post-Catalytic oxygen sensor

control integral value is over than
upper limit.

2. Post-Catalytic oxygen sensor

control integral value is lower
than lower limit.

3. Filtered Pre-Catalytic oxygen

sensor signal period is greater
than the specified value.

1. Engine Running Longer Than 60 s.

2. Coolant temperature is greater than 70°C (158 ºF).

3. Engine speed range is 1,700-2,350 rpm.

4. Oxygen sensors to the exhaust oxygen concentration

changes responding time longer than the system
preset threshold.

1. Sensor Circuit

2. Sensor

3. ECM

4. Mixture 

Too

Rich

5. Mixture 

Too

Lean

P0134

1. Signal Circuit Open.

2. Oxygen Sensors High-

Temperature and High
Resistance.

1. Engine Running Longer Than 60 s.

2. Coolant Temperature Less Than 70°C (158 ºF).

3. Duration Longer Than 25 s.

1. Sensor Circuit

2. Sensor

3. ECM

Engine

Control System JL4G15-D

2-671

3. Schematic:

12

13

D

C

A

B

Main Relay

From Battery

Pre-catalytic Oxygen Sensor

Engine 

Control 

Module

FE02-5205b

4. Diagnostic Steps:

Step 1

Connect scan tool.

Next

Step 2

Start engine and turn on the scan tool.

Next

Step 3

Maintain the engine speed at 2,500 rpm for more than 2 min to warm up the engine, until the engine coolant
temperature reaches 0°C (176 ºF).

Next

Step 4

Select on the scan tool: Engine / read data stream / group 1 oxygen sensor voltage 1 (Pre-Catalytic oxygen
sensors).

Next

Step 5

Observe oxygen sensor output voltage, which should fluctuate within 0.1-0.8 V.

2-672

Control System JL4G15-D

Engine

Yes

Intermittent Fault. Refer to 

2.2.7.3

 

Intermittent

Fault Check

No

Step 6

Carry out the oxygen sensor signal test.

(a)

If the voltage is consistently below 0.45 V (mixture too lean),
carry out the following steps:

•

Spray proper amount propane gas into intake.

•

Observe whether the Pre-Catalytic oxygen sensor
voltage has a significant change, so the voltage will rise
rapidly.

(b)

If the voltage is always higher than 0.45 V (the mixture too
rich), carry out the following steps:

•

Put the gear into neutral.

•

Apply hand brake.

•

Press the acceleration pedal so the engine speed
suddenly increased to 4,000 rpm and then quickly release
the acceleration pedal.

•

Repeat the previous step more than 3 times.

•

Check whether the Pre-Catalytic oxygen sensor voltage
has a significant change, so the voltage will rise rapidly.

During the above test, the oxygen sensor signal voltage should
have a significant change.

Does the voltage have a significant change?

Yes

Check the cause for engine Air-Fuel ratio too
thin / too rich. Refer to 

2.12.7.4

 

Symptoms

Table

.

No

Step 7

Check and confirm there is no other control system DTC code.

(a)

Connect scan tool to the datalink connector.

(b)

Turn the ignition switch to "ON" position.

(c)

Press the scan tool power button.

(d)

Select the following menu items: Engine/Read DTC codes.

(e)

Read DTC codes.

Results:

DTC Codes Shown

To Step

DTC other than P0131, P0133, P0134

No

P0131, P0133, P0134

Yes

No

Refer to 

2.12.7.14

 

DTC Code Index

Engine

Control System JL4G15-D

2-673

Yes

Step 8

Measure pre-catalytic oxygen sensor signal circuit.

FE02-5348b

A

B

C

D

Pre-catalytic Oxygen Sensor Harness 
Connector EO02

(a)

Turn the ignition switch to "OFF" position.

(b)

Disconnect oxygen sensor wiring harness connector EO02.

(c)

Turn the ignition switch to "ON" position.

(d)

Measure pre-catalytic oxygen sensor wiring harness
connector terminal No. EO02 B, the voltage between ground
and reliable value.

Standard Voltage Value: 0.35-0.5 V

(e)

Connect pre-catalytic oxygen sensor wiring harness
connector EO02.

Is the voltage specified value?

No

Go to step 11

Yes

Step 9

Measure pre-catalytic oxygen sensor ground circuit.

FE02-5349b

A

B

C

D

Pre-catalytic Oxygen Sensor Harness 
Connector EO02

(a)

Turn the ignition switch to "OFF" position.

(b)

Disconnect oxygen sensor wiring harness connector EN02.

(c)

Turn the ignition switch to "ON" position.

(d)

Measure resistance between Pre-Catalytic oxygen sensor
EO02 terminal A and a reliable ground.

Standard Resistance: Less than 1 Ω

(e)

Connect pre-catalytic oxygen sensor wiring harness
connector EO02.

Is the resistance specified value?

No

Go to step 12

Yes

Step 10

Replace the pre-catalytic oxygen sensor. Refer to 

2.4.7.2

 

Pre-Catalytic Oxygen Sensor Replacement

.

Next

Go to step 15

Step 11

Check pre-catalytic oxygen sensor signal circuit.

2-674

Control System JL4G15-D

Engine