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Inspect for any shorted or damaged wiring leading to or at the EGR itself or to any other engine comonents.Usually this is a wiring circuit fault here and usually points to the wiring at fault or possibly the egr itself needing replaced.
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With this being a short code this usually indicates a fault with the egr wiring or egr valve itself,most common the egr itself needs replaced.This system does use several sensors and components to operate and monitor the system, for proper operation.Below is the description of its operation and the components involved.
Function requirements for exhaust gas recirculation (EGR), general points - Circuit 87 ON (engine timing ON) - Engine running - Engine in load range from neutral to the upper partial-load range Exhaust gas recirculation, general The EGR lowers the nitrogen oxide (NOx) content in the exhaust gas. This occurs by means of the following 3 processes: - Reduction of the oxygen (O(2)) concentration in the combustion chamber - Reduction of the combustion temperature through reduction of the combustion speed - Reduction of the combustion temperature through a higher heat capacity of the recirculated exhaust compared to the intake air Heat capacity The heat capacity is a material property and indicates how much heat a substance can store per temperature change. Function sequence for exhaust gas recirculation EGR is active from idle through to the upper partial-load range. Determination of the EGR rate takes place depending on the following variables: - Engine load and engine rpm - Intake and charge air temperature - Exhaust temperature - Diesel particulate filter status (for code (474) Particulate filter) - Exhaust back pressure - Time limitation For this purpose, the CDI control unit (N3/9) reads signals from the following components: - Left hot film mass air flow sensor (B2/6) - Intake air temperature sensor (B2/6b1) - Right hot film mass air flow sensor (B2/7) - Intake air temperature sensor (B2/7b1) - Charge pressure sensor (B5/1) - AGR temperature sensor (B16/14) (for code (U42) BlueTEC (SCR) diesel exhaust treatment and code (494) USA version) - Charge air temperature sensor (B17/8) - Temperature sensor upstream of CAT (B19/7) (for code (U42) BlueTEC (SCR) diesel exhaust treatment - Temperature sensor upstream of diesel particulate filter (B19/9) (for code (474) Particulate filter) - Temperature sensor upstream of Turbocharger (B19/11) (for code (474) Particulate filter) - Pressure sensor downstream of air filter (B28/5) - Pressure differential sensor (DPF) (B28/8) - DPF pressure differential sensor for OBD (B28/16) (for code (U42) BlueTEC (SCR) diesel exhaust treatment and code (494) USA version)) - Accelerator pedal sensor sensor (B37) - Throttle valve, actual value potentiometer 1 (M16/6r1) - Exhaust back pressure sensor (B60) - Crankshaft Hall sensor (B70) - EGR Cooler bypass flap Hall sensor (B90) (for code (U42) BlueTEC (SCR) diesel exhaust treatment and code (494) USA version) After evaluating the input signals, the CDI control unit uses a stored performance map to actuate the left exhaust gas recirculation positioner (Y27/9) using a pulse width modulated (PWM) signal. The quantity of the recycled exhaust is increased or decreased over the left exhaust gas recirculation positioner according to actuation which is sent over a mixing tube downstream of the throttle valve actuator (M16/6) into the charge air manifold. To increase the effect of EGR, the exhaust gas is passed through the exhaust gas recirculation cooler where it is cooled. If the temperature of the recirculated exhaust gas is too low, the recirculated exhaust gas can be guided past the exhaust gas recirculation cooler via a bypass duct. If the EGR cooler bypass flap switchover valve (Y85) is actuated by the CDI control unit by means of a ground signal based on a characteristics map, then the vacuum stored in the vacuum reservoir acts on the exhaust gas recirculation cooler bypass vacuum unit and opens the bypass in the exhaust gas recirculation cooler via a linkage. The exhaust temperature determined by the exhaust gas recirculation temperature sensor is used by the CDI control unit to monitor the cooling function of the exhaust gas recirculation cooler. For vehicles with code (494) USA version the position of the bypass flap (open, closes) is determined over the EGR cooler bypass flap Hall sensor (B90). Exhaust emission standards Vehicles with code (U42) BlueTEC (SCR) diesel exhaust treatment fulfill the EU-6 exhaust emissions standard or the BIN5 LEVII exhaust emissions standard for the USA.