P0405
DTC P0405 Exhaust Gas Recirculation (EGR) Sensor Circuit Low
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 form 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 EGR Position should always be near the commanded or Desired EGR Position.
If the PCM detects a continuous short to ground in the signal circuit or the sensor, then Diagnostic Trouble Code P0405 will set. DTC P0405 is a type A code.
Conditions for Setting the DTC
- IAT is greater than 5 °C (41 °F).
- The PCM sees less than 0.10 voltage from the EGR valve sensor.
- A malfunction is present for 10 seconds.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate the first time the malfunction 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.
- A history Diagnostic Trouble Code will clear after 40 consecutive warm up cycles without a fault.
- Diagnostic Trouble Codes 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 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 set when the vehicle was cold by viewing the Engine Coolant Temperature (EGR).
Steps 1 - 8:
Steps 9 - 15:
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 creates 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 is present.
3. If the EGR valve 5 volt reference is shorted to ground, the DVM will read no voltage and an additional Diagnostic Trouble Code will be set and engine performance will be poor. When this circuit is open, only a Diagnostic Trouble Code P0405 will be set.
4. Jumping the 5 volt reference circuit to the signal circuit checks the signal circuit and PCM. The Scan Tool should display the Actual EGR Position as 100% if the signal circuit and PCM are OK.
6. Although the PCM and circuitry acted correctly in the previous step, a problem may still lie within the terminals which would not show up in probe type testing. Check the terminals for being backed out, improperly formed or damaged, and for poor tension.
10. 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 P0405 to set. Refer the EGR Valve for on vehicle service of the EGR valve.
13. The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest procedures for PCM reprogramming and Powertrain Control Module for the Tooth Error Correction Variation Procedure.
14. Check the terminals for being backed out, improperly formed or damaged, and for poor tension.