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Diagnostic Trouble Code (DTC) P0402

Exhaust Gas Recirculation Excessive Flow





Circuit Details



  • By any chance if high combustion temperatures are created by oxides of nitrogen then an Exhaust Gas Re-circulation (EGR) system which is the chief feature of this system will be boosted to counter this.
  •  This is done by supplying small amounts of exhaust gases back into the combustion chamber.
  • Combustion temperatures are minimized as soon as the air/ fuel mixture dilutes the exhaust gases.
  • The EGR valve which is linear has been specially designed to generate exhaust gases to the engine without using intake manifold vacuum.
  • This valve regulates exhaust flow entering the intake manifold from the exhaust manifold through an orifice with an ECM controlled pintle.
  • The pintle position is monitored by the ECM using inputs from the Throttle Position (TP) and the Manifold Absolute Pressure (MAP) sensor.
  • This task over, the ECM then directs the EGR valve to operate as necessary by controlling an ignition signal through the ECM.
  • The ECM further monitors the results of its command through a feedback signal.
  • The required EGR position can be checked with the help of a scan tool.
  • 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 ECM.
  • The scan tool can also be used here to note the feedback signal which is the actual position of the EGR pintle.
  • The correct EGR position should always be close to the commanded or Desired EGR position.
  • This DTC is capable of identifying an EGR open to a large valve during crank. The Crank time may be excessive with an open EGR valve.





Time for setting the DTC

Task boosted after DTC sets

When will DTC clear?

DTC  sets when

1) EGR position remains > 40% for more than 0.25 seconds during cranking (SOHC).



1) The Malfunction Indicator Lamp (MIL) will be seen glowing after three repetitively failed trips.

1) The MIL will turn off after four consecutive ignition cycles in which the diagnostic runs without a fault.

2)  EGR position remains > 70% for more than 3 seconds during cranking (DOHC).



2) The ECM will begin to store conditions which were present at the time the DTC failed.


2) De-linking the ECM battery feed for 10 seconds.

3) Engine is found cranking (not running).


3) This information will be recorded in the Freeze Frame boosting Failure Records.


3) The scan tool can be used to remove all existing DTCs.


4) Ignition voltage dwells round 10 and 16 volts.

4) A history DTC will be stored.


4) A history DTC will unset after 40 consecutive warm-up cycles without a fault.


5)  You will see that the EGR is disabled.






Diagnostic Assistance


  • Water vapor related to exhaust systems may freeze the EGR valve and make it stick in cold weather occasionally.
  • The valve will be made to get warm and normalize once it is brought to a repair shop.
  • The flaw can be detected by observing the Actual EGR and Desired EGR Positions on a cold vehicle taking a scan tool.
  • By observing the freeze frame data, the time when the DTC had set can be verified.
  • Keep the EGR Decel Filter value always at -3 or lower.
  • The EGR system will tend to become restricted in case the EGR Decel Filter number becomes more positive (towards 0 or more).
  •  Inspect and see whether there is any damage to the EGR pipe or a restriction initiated by carbon deposits in the EGR passages or on the EGR valve.





Test Description



Number(s) below refer to the step number(s) on the Diagnostic Table.




Test Description



Number(s) below indicate the step number(s) on the Diagnostic Table that follows.



1.The On-Board Diagnostic (EOBD) System Check is designed to assist the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This automatically creates an electronic copy of the data taken at the time the malfunction occurred. For future use this information is then stored on the scan tool.

2.In this step, controlling the EGR valve open informs if the EGR system can regulate the EGR valve desirably and also if any fault is present. The variation between the current and commanded position > 15%.


3.When the EGR valve electrical connector is dissociated, the scan tool is supposed to read the Actual EGR Position as 0%. In case it is not so, then the fault lies either in the EGR signal circuit or the ECM.


4.You may see a short delay in the voltage displayed on the DVM to change after the scan tool directs the EGR valve to begin.


5.An ‘open or ill connection‘status may have initiated this DTC to set. Remember to check the terminals and see that they are not being backed out, improperly formed or damaged, and for poor tension.


7.The test light must have glowed brightly in the last step if the EGR control circuit was shorted to B+ .The Actual EGR Position on the scan tool will display 100%. If the test light failed to glow then it means that the circuit may be open or shorted to ground.


9.In case the EGR valve 5 volt reference is shorted to voltage, the digital voltmeter (DVM) will accept battery voltage and additional DTCs may be set and the engine performance will tend to degenerate.


12.   The substitution of the ECM needs to be reprogrammed. You may consult the latest Techline procedure for ECM reprogramming.


13.   A problem may still lie within the terminals which may remain invisible during type testing even if the circuitry acted flawlessly during an examination. Remember to examine the terminals and see that they are not being backed out, improperly formed or damaged, and for poor tension.


17.   All circuits to the EGR valve must be functioning at this juncture. Since the fault lies internally in the EGR valve so it must be changed. Ensure that all gasket material is taken away from the EGR mounting surface. Presence of very a small amount of material may set DTC P0401.


18.   Examine the terminals and see that they are not being backed out, inaccurately formed or damaged, and have no poor tension.


19.   Removing DTCs is very essential in this step. The clearing function enables the EGR valve to relearn a new pintle position as the old pintle position was faulty on account of the failure that caused the DTC. The DTC needs to be removed keeping the ignition ON and the engine OFF or at idle. If the ECM finds any EGR command, then the new pintle will not be known.


20.   If you do not find any malfunction at this point and also no additional DTCs set, then you need to consullt  "Diagnostic Aids" in this section for additional checks and information.





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