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, P0200, P0300-P0304, P0335, P0502, P0506, P0507, and P1441 are not set. |
| • | The engine speed is between 1100-2200 RPM (manual). |
| • | The engine speed is between 1150-1700 RPM (automatic). |
| • | The Engine Coolant Temperature (ECT) is greater than 75°C (167°F). |
| • | The Barometric Pressure (BARO) is greater than 72 kPa. |
| • | The Manifold Absolute Pressure (MAP) is between 12-32 kPa. |
| • | The Throttle Position is less than 1 percent. |
| • | The vehicle speed is above 20 mph. |
| • | The EGR flow is restricted. |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM will record the operating conditions at the time during which the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The EGR is disabled. |
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 EGR Decel Filter value can be a great aid in determining if a problem exists and to verify the repairs. The EGR Decel Filter is an average of the difference in the expected MAP change and the actual MAP change that is caused by opening the EGR valve during a deceleration, and is used to determine when the MIL illuminates. This can be determined if the EGR system is OK, partially restricted or fully restricted, by driving the vehicle up to approximately 60 mph (97 km/h) and decelerating to 20 mph (32 km/h). |
| • | A more negative number (less than -3) indicates that the system is working normally whereas a positive number indicates that the system is being restricted and that the expected amount of the EGR flow is not present. A number that falls between negative 3 and positive 2 indicates that the system is partially restricted but not restricted enough to cause an impact on the emissions. |
| • | The EGR Decel Filter value should always be a -1 or lower. If the EGR Decel Filter number becomes more positive (towards 0 or more), this indicates that the EGR system is becoming restricted. Look for possible damage to the EGR pipe or for a restriction caused by carbon deposits in the EGR passages or on the EGR valve. |
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 is totally restricted or partially restricted.
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Visually and physically inspect the EGR passages and valve for excessive carbon deposits or damage.
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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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This step verifies if the fault is present and also verifies if a repair corrected the problem. Refer to Diagnostic Aids for an explanation on EGR Decel Filter. If the EGR Decel Filter value stays near 0 or a positive number after several tests have been run, then a small restriction may still exist. Be sure to check the EGR pipe for damage or dents and the EGR valve for any excessive carbon build up. Only 1 test per ignition cycle will run unless a DTC P0401 has been cleared or the battery has been disconnected.
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Clearing 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 failure that caused the DTC. The DTC must be cleared with the ignition ON, engine OFF or when the engine is idling. If the PCM sees a EGR command, the new pintle will not be learned.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||||||||||
Does the engine stall or attempt to stall? | 50% | |||||||||||
Was a repair necessary? | -- | |||||||||||
Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Is the action complete? | -- | -- | ||||||||||
Caution: Perform this step only in an area where the vehicle can operate as described without risk to other vehicles or passengers in order to prevent injury. Is the EGR Decel Filter value less than the specified value? |
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Does the scan tool indicate that this diagnostic ran and passed? | -- | |||||||||||
7 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the Applicable DTC table | System OK |
