Isuzu KB P190. Service manual — part 872

Engine Management – V6 – Diagnostics

Page 6C1-2–210

•

The internal HO2S signal voltage switches at the same rate as the heater circuit.

•

The above condition occurs 4 times out of 6 as the heater is turned off.

DTC P2251 or P2254

The ECM detects the following conditions:

•

The internal HO2S signal voltage changes greater than 10 mV as the heater control switches.

•

The above condition occurs 20 times in the last 10 seconds.

Conditions for Clearing the DTC

The HO2S signal circuit shorted to heater control circuit DTCs are Type ‘B’ DTCs. Refer to 1.4

Diagnostic Trouble

Codes in this Section, for action taken when Type ‘B’ DTC sets and conditions for clearing Type ‘B’ DTCs.

Additional Information

•

Refer to 6C1-1 Engine Management – V6 – General Information for details of the HO2S system operation.

•

For an intermittent fault condition, refer to 5.2

Intermittent Fault Conditions in this Section.

•

The HO2S must be tightened correctly. A loose HO2S will trigger these DTCs.

•

Since fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic
procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A Electrical -
Body and Chassis for information on electrical fault diagnosis.

•

To assist diagnosis, refer to 3

Wiring Diagrams and Connector Charts in this Section, for the system wiring

diagram and connector charts.

DTC P2231, P2232, P2234, P2235, P2251or P2254 Diagnostic Table

Step Action

Yes

No

1

Has the Diagnostic System Check been performed?

Go to Step 2

Refer to

4.4 Diagnostic
System Check in

this Section

2

1

Switch off the ignition for 30 seconds.

2

Start the engine.

3

Allow the engine to reach the normal operating temperature.

4

Increase the engine speed to 2,000 rpm for 10 seconds.

5

Using Tech 2, select the DTC display function.

Does DTC P2231, P2232, P2234, P2235, P2251 or P2254 fail this
ignition cycle?

Go to Step 3

Refer to Additional

Information in this

DTC

3

1

Disconnect the appropriate HO2S connector.

2

From the HO2S to the sensor wiring connector, test the
following circuit for a shorted to the sensor heater control circuit
fault condition:

•

Reference signal circuit,

•

low reference circuit,

•

pump current,

•

input pump current.

Refer to 8A Electrical - Body and Chassis for information on
electrical fault diagnosis.

Was any fault found?

Go to Step 6

Go to Step 4

Engine Management – V6 – Diagnostics

Page 6C1-2–211

Step Action

Yes

No

4

1

Disconnect the ECM and the appropriate HO2S connector.

2

From the HO2S wiring connector to the ECM wiring connector,
test the following circuit for a shorted to the sensor heater
control circuit fault condition:

•

Reference signal circuit,

•

low reference circuit,

•

pump current,

•

input pump current.

Refer to 8A Electrical - Body and Chassis for information on
electrical fault diagnosis.

Was any fault found and rectified?

Go to Step 8

Go to Step 7

6

Replace the appropriate HO2S. Refer to 6C1-3 Engine Management
– V6 – Service Operations.

Was the repair completed?

Go to Step 8

—

7

Replace the ECM. Refer to 6C1-3 Engine Management – V6 –
Service Operations.

Was the repair completed?

Go to Step 8

—

8

1

Using Tech 2, clear the DTCs.

2

Switch off the ignition for 30 seconds.

3

Start the engine.

4

Operate the vehicle within the conditions for running the DTC.

Does any of the O2 Sensor Signal Circuit Shorted to Heater Control
Circuit DTCs fail this ignition cycle?

Go to Step 2

Go to Step 9

9

Using Tech 2, select the DTC display function.

Does Tech 2 display any DTCs?

Go to the

appropriate DTC

Table in this Section

System OK

When all diagnosis and repairs are completed, check the system for correct operation.

7.59 DTC P2237, P2238, P2239, P2240, P2241

or P2242

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•

DTC P2237 – O2 Sensor Pump Current Circuit Malfunction (Bank 1, Sensor 1)

•

DTC P2238 – O2 Sensor Pump Current Circuit Low Voltage (Bank 1, Sensor 1)

•

DTC P2239 – O2 Sensor Pump Current Circuit High Voltage (Bank 1, Sensor 1)

•

DTC P2240 – O2 Sensor Pump Current Circuit Malfunction (Bank 2, Sensor 1)

•

DTC P2241 – O2 Sensor Pump Current Circuit Low Voltage (Bank 2, Sensor 1)

•

DTC P2242 – O2 Sensor Pump Current Circuit High Voltage (Bank 2, Sensor 1)

Circuit Description

The engine control relay applies positive voltage to the heater ignition voltage circuits of the HO2S #1. The ECM applies
a pulse width modulated (PWM) ground to the heater control circuit of the HO2S through a device within the ECM called
a Driver, to control the HO2S rate of heating.

The ECM maintains the voltage between the reference signal circuit and low reference circuit of the HO2S #1 to about
450 mV by increasing or decreasing the oxygen content in the HO2S diffusion gap. To achieve this, the ECM controls
the current applied to the oxygen pumping cell in the HO2S.

Engine Management – V6 – Diagnostics

Page 6C1-2–212

•

If the air / fuel mixture in the exhaust is balanced (lambda = 1), the oxygen pumping cell current is zero.

•

If the exhaust gas in the HO2S #1 diffusion gap is lean, the ECM applies a positive current to the oxygen pumping
cell to discharge oxygen from the diffusion gap.

•

If the exhaust gas in the HO2S #1 diffusion gap is rich, the ECM applies a negative current to the oxygen pumping
cell to draw oxygen into the diffusion gap.

The pumping current required to maintain the HO2S #1 signal circuit voltage to about 450 mV is proportional to the level
of oxygen concentration in the exhaust gas. The ECM monitors and evaluates the oxygen pumping current to determine
the level of oxygen concentration in the exhaust.

An HO2S pumping current control circuit DTC sets if the ECM detects the HO2S #1 signal voltage is outside the
predetermined range.

Conditions for Running the DTC

Condition 1

Run continuously once the following conditions are met:

•

DTCs P0101, P0121, P0122, P0123, P0133, P0135, P0153, P0155, P0221, P0222, P0223, P0336 and P0338 ran
and passed.

•

The ECM is commanding the lambda outside the range of 0.97 – 1.03.

•

The engine is operating in closed loop.

•

The HO2S heater is at operating temperature.

Condition 2

Run continuously once the following conditions are met:

•

DTCs P0101, P0121, P0122, P0123, P0133, P0135, P0153, P0155, P0221, P0222, P0223, P0336 and P0338 ran
and passed.

•

The ECM is commanding the lambda rich and then lean periodically with a change of greater than 2 percent.

•

The ECM detects the internal HO2S signal voltage is 1.48 – 1.52 V.

•

The HO2S is 0.97 – 1.03 lambda.

•

The engine is operating in closed loop.

•

The HO2S heater is at operating temperature.

Condition 3

Run continuously once the following conditions are met:

•

DTCs P0133 and P0153 ran and passed.

•

The HO2S heater is at operating temperature.

Conditions for Setting the DTC

Condition 1

The ECM detects the following conditions:

•

The internal HO2S signal voltage change is 1.52 – 1.48 V.

•

The above condition exists and 200 grams of exhausts gas has passed.

Condition 2

The ECM stores the fuel trim control values. This DTC sets if the ECM detects a deviation of greater than 10 percent
within 1.5 seconds between the stored value and the current value of the fuel trim.

Condition 3

The ECM detects that 5 seconds after decel fuel shut-off, the internal HO2S signal voltage is less than 1.7 V.

Engine Management – V6 – Diagnostics

Page 6C1-2–213

Conditions for Clearing the DTC

The HO2S pumping current control circuit DTCs are Type ‘B’ DTCs. Refer to 1.4 Diagnostic Trouble Codes in this
Section for action taken when Type ‘B’ DTC sets and conditions for clearing Type ‘B’ DTCs.

Additional Information

•

Refer to 6C1-1 Engine Management – V6 – General Information for details of the HO2S system operation.

•

For an intermittent fault condition, refer to 5.2

Intermittent Fault Conditions in this Section.

•

Inspect the HO2S wiring harness for contact with the exhaust system.

•

The HO2S must be tightened correctly. A loose HO2S will trigger these DTCs.

•

Since fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic
procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A Electrical-
Body and Chassis for information on electrical fault diagnosis.

•

To assist diagnosis, refer to 3

Wiring Diagrams and Connector Charts in this Section for the system wiring

diagram and connector charts.

•

The following table illustrates the typical voltages for the HO2S circuits:

HO2S Voltages

Conditions:

•

Ignition ON, Engine OFF

•

HO2S Disconnected

HO2S Circuit

Voltage

Heater Control

4.6 – 5.0 V

Heater Supply Voltage

B+

Reference Voltage

2.6 – 3.1 V

Low Reference

2.2 – 2.7 V

Pump Current

Less than 0.5 A

Input Pump Current

Less than 0.5 A

Test Description

The following numbers refer to the step numbers in the diagnostic table:

2

When performing this test, the HO2S should react immediately.

4

Connecting a jumper wire between the HO2S reference signal circuit and the low reference circuit causes the ECM
to apply signal voltage to the pumping current and input pumping current.

DTC P2237, P2238, P2239, P2240 or P2242 Diagnostic Table

Step Action Value(s)

Yes

No

1

Has the Diagnostic System Check been completed?

—

Go to Step 2

Refer to

4.4 Diagnostic

System Check

2

1

Switch off the ignition for 30 seconds.

2

Start the engine.

3

Allow the engine to reach the normal operating
temperature.

4

Increase the engine speed to 2,000 rpm for 10
seconds.

5

Using Tech 2, select the DTC display function.

Does DTC P2237, P2238, P2239, P2240, P2241,
P2242, fail this ignition cycle?

—

Go to Step 3

Refer to Additional

Information in this

DTC