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Engine exhaust gas recirculation (EGR) systems are designed to circulate exhaust gases back into the engine intake to burn soot and reduce exhaust emissions.
Vehicle engine air intake can be restricted by Carbon build up caused by exhaust gas recirculation.
Restriction of diesel engine air intake can cause running problems, loss of power and increased black smoke emissions.
Electronic engine management systems calculate required fuelling from driver demand (accelerator pedal position),
engine speed and position (crankshaft position sensor), and load by monitoring air flow volume in to the diesel engine using sensors such as :
Mass Airflow meter (MAF)
Manifold Absolute Pressure (MAP) Sensor
Turbo Boost pressure sensor to detect air flow and pressure changes.
Blocked Exhaust Gas Recirculation (EGR) systems may be detected by the engine management control computer with effect that the engine control unit program reverts engine running to a limp home function by restricting power output.
Typical symptoms include:
Loss of power making acceleration difficult
Excessive exhaust black smoke emission
The vehicle engine control computer may store a history of faults that have been detected during a journey (driving cycle).
The vehicle fault history may be logged in the vehicle engine control computer memory as fault codes, and also cause the dashboard engine management light (management information light - MIL) to come on to warn the driver that an emissions fault is present.
A dashboard mil warning light illuminated may cause the car to fail mot test.
A fault code reader connected to the vehicle diagnostic socket may be used to access fault code information and clear fault codes from ecu memory once the fault has been cured.
Typical vehicle diagnostic fault codes may include:
P0401 Insufficient or Restricted EGR Flow, .
P0405 EGR Sensor A circuit low - electrical fault which may be due to the egr valve being jammed with carbon or due to electrical deterioration and wiring faults.
EGR faults may have many causes including build up of carbon over time particularly with high mileage vehicles or vehicles completing short journeys where the engine does not get chance to warm up to temperature properly.
EGR faults may be caused by electrical wiring problems where sensor wires have broken or shorted in the engine wiring loom.
EGR faults may be caused by worn engine components such as fuel injectors where incomplete combustion occurs causing excessive emissions.
EGR faults may be caused by other system blockages such as restricted air intake due to dirty air filter, or blocked exhaust.
EGR faults may be caused by turbo boost pressure loss due to worn turbocharge or leaking air intake system.
A faulty EGR valve may require replacement
Secondary fault codes may be present.