P0404
Steps 1 - 4:
Steps 5 - 16:
Steps 17 - 19:
DTC P0404 Exhaust Gas Recirculation (EGR) Circuit Range/Performance
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 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 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 position should always be near the commanded or Desired EGR Position.
If the PCM detects a large difference between the desired EGR position and actual EGR position, then Diagnostic Trouble Code P0404 will set. DTC P0404 is a type B code.
Conditions for Setting the DTC
- IAT is greater than 5 °C (41 °F).
- EGR commanded ON (Desired EGR Position is greater than 0%).
- Actual EGR Position differs from Desired EGR Position by more than 15% for 5 seconds.
Action Taken When the DTC Sets
- Malfunction Indicator Lamp (MIL) will illuminate the second time the fault is detected.
- The PCM will record operating conditions at the time the diagnostic fails.
- A history Diagnostic Trouble Code is stored.
- The EGR Valve is disabled.
Conditions for Clearing the MIL/DTC
- The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
- Diagnostic Trouble Code(s) can be cleared by using a 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 Positions on a cold vehicle with a Scan Tool, the fault can be verified easily. Check the freeze frame data to determine if the Diagnostic Trouble Code was set when the vehicle was cold by viewing the Engine Coolant Temperature (ECT).
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart:
1. 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 created an electronic copy of the data taken when the fault occurred. The information is then stored on the Scan Tool for later reference.
2. Commanding the EGR valve open determines whether the EGR system can control the EGR valve accurately and if the fault if present.
3. When the EGR valve electrical connector is disconnected, the scan tool should display the Actual EGR Position as 0%. If is does not, the fault lies either in the EGR signal circuit or the PCM.
4. A test light, when connected to ground, 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.
5. An open or poor connection condition may have caused this Diagnostic Trouble Code to set. Be sure to check the terminals for being backed out, improperly formed or damaged, and for poor tension.
7. The test light will have glowed brightly in the previous step if the EGR control circuit was shorted to B+ 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 ground.
9. If the EGR valve 5 volt reference is shorted to voltage, the DVM will read battery voltage and additional Diagnostic Trouble Codes may be set and engine performance will be poor.
12. The replacement PCM must be reprogrammed and the Tooth Error Correction (TEC) procedure must be performed. Refer to the latest procedures for PCM reprogramming and Powertrain Control Module for the Tooth Error Correction (TEC) Procedure.
13. Although the circuitry acted correctly when checked, a problem may still lie 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, and for poor tension.
17. 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 Diagnostic Trouble Code P0401 to set. For on vehicle service of the EGR Valve, refer to EGR Valve.
18. Check the terminals for being backed out, improperly formed or damaged, and for poor tension.
19. Clearing the Diagnostic Trouble Codes 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 malfunction that caused the Diagnostic Trouble Code. The Diagnostic Trouble Code must be cleared with the ignition switch ON, with the engine OFF or when the engine is idling.
If the PCM sees a EGR command, the new pintle position will not be learned.