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10.3 Operating modes for the EGR system
There are three operating modes for the EGR system as a whole. These are listed
below with some of the failure causes. If the EGR valve is not working as expected,
then the first solution is to try and clean it. The list below gives other possible causes
if this does not work.
Mode 1:
EGR works as designed and engine produces less nitrous oxides.
This is how the designers intended it to work.
Mode 2:
Excess EGR, with symptoms of: poor idling, smoke at idling, flat
spots in acceleration, lack of power at full power.
Failure root causes for this mode include:
Fail (a): wrong signal generated by ECU - replace ECU
Fail (b): Control signal not received by solenoid - check wiring
Fail (c): solenoid not moving - replace
Fail (d): EGR valve spindle travels too far - spring has weakened -
replace
Fail (e): EGR valve spindle does not move - stuck with debris in open,
closed or intermediate position (intermittent or persistent) - clean valve
or replace
Fail (f): EGR valve spindle does not move - diaphragm torn - replace
Fail (m): idle speed too high (creates too much vacuum)
Fail (n): exhaust back pressure out of specification (e.g obstructed) -
replace exhaust
Mode 3:
No EGR effect - combustion temperature rises, adding thermal
stress to engine - possibly adverse long term reliability
consequences. Increased Nox production.
Adverse environmental
effects.
Fail (a): wrong signal generated by ECU - replace ECU
Fail (b): Control signal not received by solenoid - check wiring
Fail (c): solenoid not moving - replace
Fail (e): EGR valve spindle does not move - stuck with debris in open,
closed or intermediate position (intermittent or persistent) - clean valve
or replace
Fail (f): EGR valve spindle does not move - diaphragm torn - replace
Fail (j): Vacuum line blocked or deliberately plugged - check vacuum
pressure
Fail (k): blockage (e.g blanking plate) in pipe