Circuit Description
The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volts to the Oxygen Sensor 1 (O2S 1). The O2S 1 varies the voltage between a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if the exhaust is lean.
The O2S 1 is like an open circuit and produces no voltage when the O2S 1 temperature is below 315°C (600°F). An open O2S 1 circuit or cold sensor causes an Open Loop operation.
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 run time is greater than 25 seconds. |
| • | Engine Coolant Temperature (ECT) is greater than 70°C (158°F). |
| • | Air/fuel ratio is between 14.5:1 and 14.7:1. |
| • | Engine is operating in Closed Loop. |
| • | Throttle Position (TP) angle is between 5% and 50%. |
| Or |
| • | Engine has met the above conditions for 20 seconds. |
| • | O2S 1 voltage is less than 43 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
| • | The Fuel Pressure - System will run lean if the fuel pressure is too low. Monitor the fuel pressure while driving the vehicle at various road speeds and loads in order to confirm. Refer to Fuel System Diagnosis . |
| • | The Map Sensor - An output that causes the PCM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed (defaulted) value for the MAP sensor. When the lean condition is gone when the sensor is disconnected, substitute a known good sensor and recheck. |
| • | A fuel contamination - Water, in even small amounts, near the fuel pump inlet can be delivered to the fuel injector. The water causes a lean exhaust and a DTC P0131 can set. |
| • | The O2S harness - the O2S 1 pigtail may be mis-positioned and contacting the exhaust manifold. |
| • | An engine misfire A misfire will result in unburned oxygen in the exhaust, which can cause DTC P0131. Go to DTC P0300 Engine Misfire Detected and the Driveability Symptoms. |
| • | A cracked Oxygen sensor (O2S) - A cracked O2S or poor ground at the sensor can cause a DTC P0131. Go to the Driveability Symptoms. |
| • | A plugged fuel filter - A plugged fuel filter can cause a lean condition and cause a DTC P0131 to set. |
| • | A plugged Oxygen Sensor (O2S) - A plugged reference port on the Oxygen Sensor (O2S) will indicate a lower then normal voltage output from the O2S. |
Whenever the oxygen sensor pigtail wiring, connector or 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 O2S must have a clean air reference provided. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the O2S sensor wires, connectors or terminals could result in the obstruction of the air reference degrading the performance of the oxygen sensor.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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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 in the scan tool for later reference.
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This step determines if DTC P0131 is the result of a hard failure or an intermittent condition. It may be necessary to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction detected by the PCM.
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This step simulates a DTC P0134. If the PCM senses the change, the PCM and wiring are OK.
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Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the Powertrain Control Module (PCM) .
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If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
Does the O2S 1 voltage remain below the specified value? | 43 mV | |||
3 |
Does the O2S 1 voltage stay below specified value? | 43 mV | ||
Does the scan tool indicate that the O2S 1 voltage is within the specified values? | 407-509 mV | |||
5 | Check the O2S 1 sensor signal circuit for a short to ground and repair as necessary. Was a repair necessary? | -- | ||
Check for poor connections at the PCM. If OK, replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
7 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK Refer to Diagnostic Aids |
