Circuit Description
An exhaust gas recirculation (EGR) system is used in order to lower oxides of nitrogen (NOx) emission levels caused by high combustion temperatures. The EGR 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 in order 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 control module controlled pintle valve. The control module commands the EGR by applying a 12 volt duty cycle to the EGR valve. This can be monitored on a scan tool as desired EGR position.
The control module can monitor the pintle position with the EGR pintle position signal. This sensor uses a variable resistor with a 5 volt reference, a signal circuit, and a ground. The signal circuit monitors changes in voltage on the variable resistor as the pintle moves.
Conditions for Running the DTC
| • | The engine coolant temperature (ECT) is between 80-120°C (176-248°F. |
| • | The intake air temperature (IAT) is less than 100°C (212°F). |
| • | The desired exhaust gas recirculation (EGR) position is more than 15 percent. |
Conditions for Setting the DTC
| • | The EGR pintle position is 4 percent or more with the EGR valve commanded closed. |
| • | The above condition exists for more than 10 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) the first time the diagnostic runs and fails. |
| • | The control module will set the DTC and records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
This diagnostic will detect an EGR pintle that does not return to the learned closed position due to foreign material lodged in the pintle seating area or a defective EGR valve. The VCM will attempt to clear the EGR valve of any foreign material by commanding the EGR valve fully open, although the vehicle must be at cruising speed for this to occur. If the third attempt to clear the valve is unsuccessful, then DTC P1404 will set.
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Commanding the EGR valve open and closed determines whether the EGR system can control the EGR valve accurately and if the EGR valve will return to the fully closed position. Not all vehicles will display actual EGR at 100 percent.
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When the EGR valve harness connector is disconnected, the scan tool should display the Actual EGR Position as 0 percent. If it does not, the malfunction lies either in the EGR signal circuit or the VCM.
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If the EGR valve 5.0 volt reference is shorted to voltage, the DMM will read battery voltage and additional DTCs may be set.
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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 minimum pintle position as the old position was inaccurate due to the malfunction that caused the DTC. If the VCM sees an EGR command, the new minimum pintle position will not be learned.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the Actual EGR Position follow the Commanded EGR Position and return to 0 percent? | 20%, 50%, 70%, 100% | |||
3 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids |
Disconnect the EGR valve harness connector. Is the Actual EGR Position near the specified value? | 0% | |||
5 |
Did you find a problem? | -- | ||
Probe the EGR valve 5 volt reference circuit at the EGR valve harness connector with a DMM connected to a ground. Is the voltage near the specified value? | 5.2 V | |||
7 | Probe the EGR valve feed control circuit at the EGR valve harness connector with a test lamp connected to a ground. Is the test lamp ON? | -- | ||
8 |
Did you find a problem? | -- | ||
9 |
Did you find a problem? | -- | ||
10 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Is the action complete? | -- | -- | |
11 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
Does the scan tool indicate that this diagnostic Passed? | -- | |||
13 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
