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 powertrain control module (PCM) 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 powertrain control module (PCM) 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 ECT is between 80-120°C (176-248°F). |
| • | The IAT is less than 100°C (212°F). |
| • | The desired EGR position is more than 15 percent. |
Conditions for Setting the DTC
| • | The EGR pintle position voltage is 4 percent or more with the EGR valve commanded closed. |
| • | The vehicle must be driven. |
| • | The above condition exists for more than 10 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
This diagnostic will detect the EGR pintle position not returning to the learned closed position due to foreign material lodged in the pintle seating area, or due to a defective EGR valve. The PCM will command the EGR valve fully open to attempt to clear the valve of any foreign material, although the vehicle must be at cruising speed for this to occur. If the third attempt to clear the valve is unsuccessful, the code 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 inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent 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 PCM.
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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 PCM sees an EGR command, the new minimum pintle position will not be learned.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the Actual EGR Position follow the Commanded EGR Position and return to 0 percent? | 20%, 50%, 70%, 100% | Go to Step 3 | Go to Step 4 | |
3 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Aids | |
Disconnect the EGR valve harness connector. Is the Actual EGR Position near the specified value? | 0% | Go to Step 6 | Go to Step 5 | |
5 |
Did you find a problem? | -- | Go to Step 12 | Go to Step 11 |
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 | Go to Step 7 | Go to Step 8 | |
7 | Probe the EGR valve control circuit at the EGR valve harness connector with a test lamp connected to a ground. Is the test lamp ON? | -- | Go to Step 9 | Go to Step 10 |
8 |
Did you find a problem? | -- | Go to Step 12 | Go to Step 11 |
9 |
Did you find a problem? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Is the action complete? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 12 | -- |
Does the scan tool indicate the diagnostic Passed? | -- | Go to Step 13 | Go to Step 2 | |
13 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK | |
