Refer to
EVAP and EGR Controls
for wiring view.
Circuit Description
An Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures. It accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, 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 intake manifold vacuum. The valve controls 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 using inputs from the Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensors. The PCM then commands the EGR valve to operate when necessary by controlling a ground signal through the PCM. This can be monitored on a scan tool as the Desired EGR Position. Ignition voltage is supplied to the valve through a fuse.
The PCM monitors the results of its 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 is sent 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 Desired EGR Position .
Conditions for Setting the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, 118, 0121, 0122, 0123, 0125, 0200, 0300-P0304, 0335, 0440, 0442, 0446, 0502, 0503, 0506, 0507, and P1441 are not set. |
| • | The ignition voltage is greater than 12V. |
| • | The EGR signal has no voltage signal for 2 seconds. |
| OR |
| With EGR commanded OFF (Desired EGR Position is 0%). |
| • | Actual EGR Position is greater than 3% for 25 seconds. |
| • | Actual EGR Position differs from Desired EGR Position by more than 6% for 20 seconds. |
| OR |
| With EGR commanded ON (Desired EGR Position is greater than 0%). |
| • | Actual EGR Position differs from Desired EGR Position by more than 9% for 18 seconds when desired EGR is less than 99%. |
| • | Actual EGR Position differs from Desired EGR Position by more than 20% for 18 seconds when desired EGR is greater than 99%. |
Action Taken When the DTC Sets
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer. |
| • | A history DTC is stored. |
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. |
| • | The MIL/DTCs can be cleared by using the scan tool. |
Diagnostic Aids
Due to the moisture 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 Desired EGR Position on a cold vehicle with a scan tool, the fault can be verified easily. View the freeze frame data to determine if the DTC set when the vehicle was cold by viewing both the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT).
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.
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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, go directly to step 11, as the fault lies either in the EGR signal circuit or the PCM. If the problem is in the EGR ignition feed circuit, other circuits that share this ignition feed will also experience a problem unless the circuit is open only on the EGR valve side of the spliced circuit.
-
A test light, when connected to B+, 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.
-
If the open condition was due to a open fuse, locate and repair any shorts that may have caused the fuse to open before replacement.
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If the EGR valve 5 volt reference is shorted to voltage, the DVM will read battery voltage and an additional DTC will be set and engine performance will be poor. When this circuit is open, an additional DTC may also be set if the entire circuit is open. Only a DTC P1406 set indicates that the circuit is open between the EGR valve electrical connector and the spliced circuit.
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The test light will have glowed brightly in step 5 if the EGR control circuit was shorted to ground 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 voltage.
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If the 5 volt reference circuit is shorted to ground, an additional DTC will also be set. If no other DTCs are set, then the fault must be between the EGR valve electrical connector and the 5 volt reference splice to the throttle position sensor.
-
The Actual EGR Position should read 0% before jumping the 5 volt reference circuit to the signal circuit. If any other reading is present, then either the signal circuit or the PCM is at fault.
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An open or short in the EGR valve sensor ground circuit will also cause an additional DTC to be set. If no other DTCs are set, and the circuit is found to be open or shorted, the fault is on the EGR valve side of the spliced circuit.
-
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 .
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An open in the EGR signal circuit will always display the Actual EGR Position as 0%. A short to ground will display the Actual EGR Position as 0% and a short to voltage as 10 %.
-
The replacement PCM must be reprogrammed. Refer to the latest Techline procedures for PCM Reprogramming.
-
If no faults 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 the Actual EGR Position A follow the Desired EGR Position ? | 25%, 50%, 75%, 100% | |||||||||
Does the test light illuminate? | -- | |||||||||
As the commanded percentage is raised, does the test light:
| 25%, 50%, 75%, 100% | |||||||||
Repair the open in the EGR valve ignition feed circuit. Is the action complete? | -- | -- | ||||||||
Using a DVM connected to ground, probe the 5 volt reference circuit to the EGR valve. Does the DVM read the specified value? | 5.0V | |||||||||
Check for an open or a short in the EGR control circuit and repair as necessary. Was a repair necessary? | -- | |||||||||
8 | Using a DVM connected to B+, probe the EGR valve sensor ground circuit. Does the DVM read the specified value? | B+ | ||||||||
Check for an open or a short in the EGR valve 5 volt reference circuit and repair as necessary. Was a repair necessary? | -- | |||||||||
Jumper the EGR valve 5 volt reference circuit to the signal circuit. Does the Actual EGR Position display the specified value? | 100% | |||||||||
Check for an open in the EGR valve sensor ground circuit and repair as necessary. Was a repair necessary? | -- | |||||||||
Replace the EGR valve. Is the action complete? | -- | -- | ||||||||
Check for an open or a short in the EGR valve signal circuit and repair as necessary. Was a repair necessary? | -- | |||||||||
Replace the PCM. Is the action complete? | -- | -- | ||||||||
15 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||||||||
Check if any additional DTC's are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK Refer to Diagnostic Aids |
