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Isuzu engine C22NE / 22LE / 20LE. Manual - part 80

DRIVEABILITY AND EMISSIONS 6E1-149

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 45)

O2 SENSOR TOO RICH (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 320mV. The oxygen sensor

varies the voltage within a range of about 900mV

when the exhaust is rich, down through about 10mV

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

high for an extended period of time.

This code detects a rich 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%.
• Following Diagnostic Trouble Codes are not set:

Malfunction DTC: 21, 22, 33, 24

• Closed Loop fuel integrator is not reset and closed

loop fuel enabled.

Action Taken When the DTC Sets

• The ECM will illuminate the malfunction indicator

lamp (MIL).

• "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.

6E1-150 DRIVEABILITY AND EMISSIONS

Diagnostic Aids

Check the following items:
• Fuel pressure - The system will go rich if pressure

is too high. The ECM can compensate for some

increase. However, if fuel pressure is too high, a

Diagnostic Trouble Code 45 may be set. Refer to

Fuel System Diagnosis.

• Perform "Injector Balance Test" - Refer to Fuel

System Diagnosis.

• Check the EVAP canister for fuel saturation - If full

of fuel, check canister control and hoses. Refer to

Evaporative (EVAP) Emission Control System.

• Check for a leak in the fuel pressure regulator

diaphragm by checking the vacuum line to toe

regulator for the presence of fuel.

• An intermittent TP sensor output will cause the

system to go rich due to a false indication of the

engine accelerating.

• Silicon contamination of the HO2S can also cause a

high HO2S voltage to be indicated. This condition is

indicated by a powdery white deposit on the portion

of the HO2S exposed to the exhaust stream. If

contamination is noticed, replace the affected

HO2S.

• Operate the vehicle while monitoring the HO2S

voltage with a Scan Tool. If the HO2S voltage is

limited within a range between 300mV to 600mV,

check the HO2S high and low circuit wiring and

associated terminal connections. If the wiring and

connections are OK, replace the HO2S.

DTC (Flash DTC = 45)

O2 Sensor Too Rich

Step

Action

Value(s)

Yes

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

performed?

Go to Step 2

Go to OBD

System

Check

1. Install the Scan Tool.

2. Run the engine at operating temperature.

3. Operate the vehicle within parameters specified under

"Conditions for Setting the Diagnostic Trouble Code".

4. Using a Scan Tool, monitor HO2S voltage.

Does the HO2S voltage remain above the specified value?

952 mV

(500mV in

deceleration

fuel cutoff

mode)

Go to Step 4

Go to Step 3

1. Ignition ON.

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

Code 45.

3. Does the Scan Tool indicate Diagnostic Trouble Code

45.

Refer to

Diagnostic

Aids

Go to Step 4

1. Ignition OFF.

2. Disconnect HO2S.

3. Ignition ON.

4. At HO2S connector (ECM side) use a DVM to measure

voltages at the high and low signal terminals.

Are the voltages in the specified range?

5-14V

Go to Step 5

Go to Step 6

Repair short to voltage in signal circuit.

Verify repair

1. Ignition OFF.

2. Disconnect the ECM connector.

3. Check for damage to the ECM pins and terminals.

Was a problem found?

Verify repair

Go to Step 7

DRIVEABILITY AND EMISSIONS 6E1-151

DTC (Flash DTC = 45)

02 Sensor Too Rich (Cont’d)

Step

Action

Value(s)

Yes

1. Ignition ON, engine OFF.

2. Disconnect HO2S and jumper the HO2S high and low

circuits (ECM side) to ground.

3. Using a Scan Tool, monitor HO2S voltage.

Is HO2S voltage below the specified value?

10mV

Go to Step 8

Go to Step 9

Replace HO2S.

Is the action complete?

Verify repair

Replace the EPROM or ECM.

Is the action complete?

Note) Refer to 6E1-243.

Verify repair

6E1-152 DRIVEABILITY AND EMISSIONS

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