Isuzu engine C22NE / 22LE / 20LE. Manual — part 79

DRIVEABILITY AND EMISSIONS 6E1-145

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 44)

O2 SENSOR TOO LEAN (IF APPLICABLE)

Circuit Description

The engine control module (ECM) supplies a bias

voltage of about 450mV between the heated oxygen

sensor (HO2S) signal and low circuits. When

measured with a 10 megaohm digital voltmeter, this

may display as low as 350mV. The oxygen sensor

varies the voltage within a range of about 900mV

when the exhaust is rich, down through about 60mV

when exhaust is lean. The ECM constantly monitors

the HO2S signal during "Closed Loop" operation and

compensates for a rich or lean condition by

decreasing or increasing injector pulse width as

necessary. If the HO2S voltage remains excessively

low for an extended period of time.

This code detects a lean oxygen sensor reading.

Conditions for Setting the DTC

• Engine run time is longer than 60sec.
• Engine coolant temperature is above 70 °C(158°F).
• Throttle angle is greater than 5%.

All above conditions met and the following condition is

met:
• HO2S signal voltage remains less than 274mV.

Action Taken When the DTC Sets

• The ECM will illuminate the malfunction indicator

lamp (MIL) the first time the fault is detected.

• "Open Loop" fuel control will be in effect.

Conditions for Clearing the MIL/DTC

Once the ECM determines that a fault(s) has been

rectified then the CEL will switch OFF, although the

fault code will remain in the ECM memory.

Any fault codes will remain in ECM memory until -

1. They are cleared by disconnecting the Battery for

more than 30 seconds.

2. A service tool such as Tech 2 is used to clear them.

3. Ten consecutive starts without logging a fault.

6E1-146 DRIVEABILITY AND EMISSIONS

Diagnostic Aids

Check for the following conditions:
• Heated oxygen sensor wiring - The sensor pigtail

may be routed incorrectly and contacting the

exhaust system.

• Poor ECM to engine block ground.
• Fuel pressure - The system will go lean if pressure

is too low. The ECM can compensate for some

decrease. However, if fuel pressure is too low, a

diagnostic Trouble Code 44 may be set. Refer to

Fuel System Diagnosis.

• Lean injector(s) - Perform "Injector Balance Test."
• Vacuum leaks - Check for disconnected or

damaged vacuum hoses and for vacuum leaks at

the intake manifold, throttle body, and PCV system.

• Exhaust leaks - An exhaust leak may cause outside

air to be pulled into the exhaust gas stream past the

HO2S, causing the system to appear lean. Check

for exhaust leaks that may cause a false lean

condition to be indicated.

• Fuel contamination - Water, even in small amounts,

can be delivered to the fuel injectors. The water can

cause a lean exhaust to be indicated, Excessive

alcohol in the fuel can also cause this condition.

Refer to Fuel System Diagnosis for the procedure

to check for fuel contamination.

If none of the above conditions are present, replace

the affected HO2S.

DTC (Flash DTC = 44)

O2 Sensor Too Lean

Step

Action

Value(s)

Yes

No

1

Was the "On-Board Diagnostic (OBD) System Check"

performed?

-

Go to Step 2

Go to OBD

System

Check

2

1. Install the Scan Tool.

2. Run the engine at operating temperature.

3. Operate the vehicle within the parameters specified

under "Conditions for Setting the Diagnostic Trouble

Code" criteria included in Diagnostic Support.

4. Using a Scan Tool, monitor HO2S voltage.

Does the HO2S voltage remain below the specified value?

300mV

Go to Step 4

Go to Step 3

3

1. Ignition ON, engine OFF.

2. Using a Scan Tool, monitor info for Diagnostic Trouble

Code 44.

-

Go to Step 4

Refer to

Diagnostic

Aids

4

1. Turn the ignition OFF.

2. Disconnect the ECM.

3. Check the HO2S high and low circuits for a short to

ground or a short to the heater ground circuit.

Are the HO2S signal circuits shorted to ground?

-

Go to Step 5

Go to Step 6

5

Repair the HO2S signal circuit.

Is the action complete?

-

Verify repair

-

6

1. Turn the ignition OFF HO2S and ECM disconnected.

2. Check for continuity between the high and low signal

circuits.

Was there continuity between the high and low circuits?

-

Go to Step 7

Go to Step 8

7

Repair the short between the high and low circuits.

Is the action complete?

-

Verify repair

-

DRIVEABILITY AND EMISSIONS 6E1-147

DTC (Flash DTC = 44)

O2 Sensor Too Lean (Cont'd)

Step

Action

Value(s)

Yes

No

8

1. Ignition OFF.

2. Reconnect the ECM, leave the sensor disconnected.

3. Ignition ON.

Does the Scan Tool indicate HO2S voltage near the

specified value?

430-450mV

Refer to

Diagnostic

Aids

Go to Step 9

9

Replace the EPROM or ECM.

Is the action complete?

Note) Refer to 6E1-243.

-

Verify repair

-

6E1-148 DRIVEABILITY AND EMISSIONS