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.
The vehicle control module (VCM) will set a DTC P0404 if it detects a large enough difference between the commanded EGR and the actual EGR.
Conditions for Running the DTC
| • | No active manifold absolute pressure (MAP) sensor DTCs |
| • | No active intake air temperature (IAT) sensor DTCs |
| • | No active engine coolant temperature (ECT) sensor DTCs |
| • | No active throttle position (TP) sensor DTCs |
| • | No active evaporative emissions (EVAP) system DTCs |
| • | No active idle air control (IAC) DTCs |
| • | DTC P0300, P1336 or P1404 are not active |
| • | The system voltage is more than 11.7 volts |
| • | The desired EGR position is more than 0 percent |
Conditions for Setting the DTC
The difference between the actual EGR position and the desired EGR position is more than 10 percent for more than 10 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool 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
Excessive carbon deposits may case a restriction of movement in the EGR pintle. This problem may be compounded in cold weather with moisture freezing in the valve. Inspect for full range operation in the EGR system with the scan tool. Refer to Restricted Exhaust in Engine Exhaust.
Inspect for intermittents.
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 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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This step will determine if the VCM can control the EGR valve.
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Commanding the EGR valve to the specified values determines whether the VCM can control the EGR valve accurately. Production variations may not allow the EGR valve to be commanded to 100 percent.
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There are certain circuits in the VCM C4 connector that could cause a short to voltage to the EGR valve control circuit that may disappear when the C4 connector is disconnected. By checking each individual circuit for a short to the EGR valve control circuit with a DMM will confirm if such a condition exists.
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If the EGR valve 5 volt reference is shorted to voltage, the DMM will read battery voltage and additional DTCs may be set.
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A problem may exist 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.
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A problem may exist 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.
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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.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic System Check? | -- | ||
Does the engine run rough or stall? | 50% | |||
Does the actual EGR position closely follow the commanded EGR position? | 0%, 20%, 50%, 70%, 100% | |||
4 | This DTC is intermittent. Are any other DTCs set? | -- | Go to the applicable DTC table | Go to Diagnostic Aids |
5 |
Does the test lamp illuminate? | 100% | ||
6 | Probe the EGR valve ground circuit at the EGR valve connector with a test lamp connected to B+. Does the test lamp illuminate? | -- | ||
7 | Inspect the EGR valve control circuit for a short to ground between the VCM and the EGR valve harness connector using a test lamp connected to B+. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem? | -- | ||
8 | Inspect the EGR valve control circuit for an open between the VCM and the EGR valve electrical connector using a DMM. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem? | -- | ||
9 | Inspect the EGR valve ground circuit for an open. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem? | -- | ||
10 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Does the test lamp illuminate? | -- | ||
11 |
Does the test lamp illuminate? | -- | ||
Are there any circuits shorted to the EGR valve control circuit? | -- | |||
Use a DMM in order to measure the voltage at the EGR valve connector between the 5 volt reference circuit and ground. Is the voltage more than the specified value? | 5.2 V | |||
14 | Use a DMM in order to measure the voltage at the EGR valve connector between the EGR pintle position signal circuit and ground. Is the voltage at the specified value? | 0 V | ||
15 | Test the pintle position signal circuit between the EGR valve electrical connector and the VCM for a short to voltage. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem? | -- | ||
16 | Probe the EGR sensor ground circuit at the EGR valve electrical connector with a test lamp connected to B+. Does the test lamp illuminate? | -- | ||
17 | Repair the short to voltage to the EGR valve control circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
18 | Repair the short to the EGR valve control circuit. Refer to Wiring Repairs or to Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |
19 | Repair the short to voltage in the 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
20 |
Did you find a problem? | -- | ||
Inspect for a poor connection at the EGR valve. Refer to Connector Repairs in Wiring Systems. Did you find a problem? | -- | |||
22 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Is the action complete? | -- | -- | |
Inspect the VCM connectors for a poor connection. Repair as necessary. Refer to Connector Repairs in Wiring Systems. Did you find a problem? | -- | |||
24 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
Does the scan tool indicate the diagnostic Passed? | -- | |||
26 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to applicable DTC table | System OK |
