Circuit Description
The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal relative to the oxygen storage capacity of the catalytic converter. The PCM can then determine the ability of the catalytic converter to convert the exhaust emissions effectively. The HO2S 2 signal will be far less active than the signal produced by the front Oxygen Sensor 1 (O2S 1).
Conditions for Setting the DTC
| • | DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0301, P0302, P0303, P0304, P0404, P0405, P0506, P0507, P1404, P1441 not set. |
| • | Engine has been running longer than 30 seconds. |
| • | Engine Coolant Temperature (ECT) is greater than 40°C (104°F). |
| • | Throttle Position (TP) is between 5% and 50%. |
| • | HO2S 2 remains between 425 mV and 460 mV for 125 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | The malfunction indicator lamp (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
Whenever the oxygen sensor pigtail wiring, the connector, or the terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, connector or terminals. In order for the sensor to function properly, the rear HO2S 2 must have a clean air reference. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference and degrade the performance of the oxygen sensor.
A poor connection, rubbed through wire insulation or a wire broken inside the insulation may cause an intermittent.
Check for the following conditions:
| • | A poor connection or damaged harness - Inspect the PCM harness for the following condition: |
| - | Open in the rear HO2S high circuit |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| - | Damaged harness. |
| • | An intermittent test - Observe the rear HO2S 2 on the scan tool while moving the related connectors and wiring harness with the key ON. Whenever the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
-
This step determines if DTC P0140 is the result of a hard malfunction or an intermittent condition.
-
Disconnecting the HO2S 2 and jumpering the HO2S 2 signal and the HO2S 2 low circuits to ground will determine if the PCM or wiring or HO2S 2 is malfunctioning.
-
Determines which circuit the malfunction is in. If the HO2S 2 signal and the HO2S 2 low circuits are OK, then the PCM connection or PCM is malfunctioning.
-
Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the Powertrain Control Module (PCM) .
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
Does the scan tool display a HO2S 2 voltage between the specified value? | 80°C (176°F) 1200 RPM 425 mV-460 mV (0.425V-0.460V) | |||
3 |
Does the scan tool display the HO2S 2 voltage steady around the specified value? | 425 mV-460 mV (0.425V-0.460V) | ||
Does the scan tool display the HO2S 2 voltage below the specified value? | 100 mV (0.10V) | |||
5 |
Refer to Electrical Diagnosis . Was a repair necessary? | -- | ||
Does the test light illuminate? | -- | |||
7 | Replace the HO2S 2 sensor. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |
8 | Check for an open in the HO2S 2 high circuit or poor connection and repair as necessary. Was a repair necessary? | -- | ||
9 | Repair the open in the HO2S 2 low circuit. Is the action complete? | -- | -- | |
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
11 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||
12 | Check if any additional DTCs are set. Are any DTCs are set. Are any additional DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
