Circuit Description
An Exhaust Gas Recirculation (EGR) system lowers the Oxides of Nitrogen (NOx) emission levels that are caused by high combustion temperatures. This is accomplished by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, the combustion temperatures are reduced.
A linear EGR valve is used on this system. The linear EGR valve is designed to accurately supply exhaust gases to the engine without the use of the intake manifold vacuum. The valve controls the exhaust flow going into the intake manifold from the exhaust manifold through an orifice with a PCM controlled pintle. The PCM controls the pintle position by using inputs from the Throttle Position (TP) sensor and the Manifold Absolute Pressure (MAP) sensor. The PCM then commands the EGR valve to operate when necessary by controlling an ignition signal through the PCM. This can be monitored on a scan tool as the Desired EGR Position.
The PCM monitors the results of the command through a feedback signal. By sending a 5 volt reference and a ground to the EGR valve, a voltage signal representing the EGR valve pintle position travels to the PCM. This feedback signal can also be monitored on a scan tool and is the actual position of the EGR pintle. The Actual EGR Position should always be near the commanded or the Desired EGR Position.
Conditions for Setting the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0300-P0304, P0335, P0440, P0442, P0446, P0506, P0507, P1336, P1404 and P1441 are not set. |
| • | The ignition voltage is greater than 11.7 V. |
| • | The EGR commanded ON (The Desired EGR Position is greater than 0 percent). |
| • | The Actual EGR Position differs from the Desired EGR Position by more than 9 percent for 18 seconds. |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) will illuminate. |
| • | The PCM will record operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | A history DTC is stored |
| • | The EGR Valve is disabled. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three 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. |
| • | A scan tool clears the DTCs. |
Diagnostic Aids
Due to the moisture that is associated with exhaust systems, the EGR valve may freeze and stick in colder weather at times. After the vehicle is brought into a warm shop for repairs, the valve warms and the problem disappears. By watching the Actual EGR and the Desired EGR Positions on a cold vehicle with a scan tool, you can easily verify the malfunction. Check the freeze frame data in order to determine if the DTC set when the vehicle was cold by viewing the Engine Coolant Temperature (ECT).
If a condition occurs where the EGR valve signal is pulled low (but not to zero), the PCM will learn the new lower value as zero. When the EGR valve signal returns to normal the PCM interprets this as a value indicating that the EGR valve did not close and may set this DTC.
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 fault occurred. The information is then stored on the scan tool for later reference.
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Commanding the EGR valve open determines whether the EGR system can control the EGR valve accurately and if the fault is present.
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When the EGR valve electrical connector is disconnected, the scan tool should display the Actual EGR Position as 0%. If it does not, the fault lies either in the EGR signal circuit or the PCM.
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A test light, when connected to ground, will glow dimly when the EGR valve is commanded to 25%, and brighter as the EGR valve is commanded to 100%. If the test light flashes, check the sensor ground for an open.
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An open or poor connection condition may have caused this DTC to set. Be sure to check the terminals for being backed out, improperly formed or damaged, and for poor tension.
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The test light will have glowed brightly in the previous step if the EGR control circuit was shorted to B+ and the Actual EGR Position on the scan tool will display 100%. A test light that did not illuminate, indicates that the circuit may be open or shorted to ground.
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If the EGR valve 5 volt reference is shorted to voltage, the DVM will read battery voltage and additional DTCs may be set and engine performance will be poor.
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The replacement PCM must be reprogrammed and the crankshaft reluctor variation procedure must be performed. Refer to the latest Isuzu Technical Communication System (ITCS) procedures for PCM reprogramming and Powertrain Control Module (PCM) (General Description) for the Crankshaft Reluctor Variation Procedure .
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Although the circuitry acted correctly when checked, a problem may still lie within the terminals which would not show up in probe type testing. Be sure to check the terminals for being backed out, improperly formed or damaged, and for poor tension.
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All circuits to the EGR valve are OK at this point. The fault lies internally in the EGR valve and therefore must be replaced. Be sure all gasket material is removed from the EGR mounting surface. Even a small amount of material may cause a DTC P0401 to set. Refer to Exhaust Gas Recirculation Valve Replacement for on vehicle service of the EGR valve.
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Check the terminals for being backed out, improperly formed or damaged, and for poor tension.
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Clearing the DTCs is a very important step for this diagnostic. The clearing function allows the EGR valve to relearn a new pintle position as the old position was inaccurate due to the malfunction that caused the DTC. The DTC must be cleared with the ignition switch ON, with the engine OFF or when the engine is idling. If the PCM sees a EGR command, the new pintle position will not be learned.
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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? | -- | |||
Does theActual EGR Position follow the Desired EGR Position ? | 25%, 50%, 75%, 100% | |||
Does the test light illuminate? | -- | |||
As the command is raised, does the test light glow brighter, flash or maintain a steady glow? | 25%, 50%, 75%, 100% | |||
Repair the open or poor connection in the EGR ground circuit. Is the action complete? | -- | -- | ||
6 | With the test light still connected to ground, probe the signal circuit. Does the test light illuminate? | -- | ||
With the test light still connected to ground, again probe the control circuit without commanding the EGR valve with the scan tool. Does the test light illuminate? | -- | |||
8 | Check the signal circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | ||
With a DVM connected to ground, probe the 5V reference circuit. Is the voltage measured near the specified value? | 5V | |||
10 | Check the control circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | ||
11 | Connect the test light to B+ and again probe the control circuit. Does the test light illuminate? | -- | ||
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
Check the EGR ground circuit for a poor connection or proper terminal tension at the PCM and repair as necessary. Was a repair necessary? | -- | |||
14 | Check the 5V reference circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | ||
15 | Check the control circuit for a short to ground and repair as necessary. Was a repair necessary? | -- | ||
16 | Check the control circuit for an open or poor connection at the EGR valve electrical connector and repair as necessary. Was a repair necessary? | -- | ||
Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Is the action complete? | -- | -- | ||
Check the PCM electrical connector for a poor connection and repair as necessary. Was a repair necessary? | -- | |||
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 the applicable DTC table | System OK, refer to Diagnostic Aids |
