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3467

OBD-System

OBD and exhaust gas return system

Pierburg | Motorservice

The on-board diagnostics shows a fault in the exhaust gas recirculation system, but what does the displayed diagnostic trouble code mean? Here, you will find out the meaning behind the diagnostic trouble codes P0400, P0401, P0402, P0403, P0404, P0405, P0406, P0407 and P0408 and what you can do to resolve the issue.

3467
PIERBURG PRODUCTS ON-BOARD DIAGNOSTICS
01 EGR coolers 09 Engine control unit
02 Intake manifold 10 Malfunction indicator lamp (MIL)
03 Air mass sensor (LMS) 11 Diagnostic plug
04 Pneumatic EGR valve (petrol) 12 OBD data scan tool
05 Electric EGR valve (petrol)
06 Electromotive EGR valve (diesel)
07 Pneumatic EGR valve (diesel)
08 Electropneumatic pressure transducer (EPW)
for pneumatic EGR valves

FROM PRACTICAL USE

3468
Blocked air mass sensor (LMS)
3470
Carbonised EGR valve (petrol) with zoom
3469
Stuck EGR valve (diesel) and in new condition

FINDING AND REMEDYING FAULTS

DIAGNOSTIC TROUBLE
CODE
P0400 P0401 P0402
DISPLAYED FAULTS EGR system – flow malfunction
The EGR valve does not open:
• There is no exhaust gas
recirculation, or it is not detected
• Output not reached
• Engine goes into limp home
function
• Driving behaviour is deficient
• Uneven idling
EGR system – insufficient flow rate
Not enough exhaust gas is being
recirculated:
• EGR valve does not open wide
enough
• Cross section restricted by
impurities (carbon deposits)
• EGR valve opening time too short
• Air mass sensor defective or soiled
EGR system – excessive flow rate
Too much exhaust gas is being
recirculated:
• EGR valve opens to an extent that
deviates from the set-point values
• Valve does not close completely
• Air mass sensor defective or soiled
NEXT STEPS/
POSSIBLE REMEDIES
• Check pneumatic EGR valve with
vacuum hand pump:
If the vacuum is not maintained,
replace the EGR valve; check the
vacuum lines for free flow/
tightness
• Examine the EGR valve for visible
damage or discolouration:
   - Exhaust gas back pressure could
   be too high or the actuation could
   be incorrect
   - Check the exhaust system for
   free flow
• If there is sticking, replace the
EGR valve and check the fuel
injection system and the oil vapour
separator (blow-by separator)
• Check the power supply to the
EGR valve and electropneumatic
pressure transducer
• Check electric actuators
• Check pneumatic actuators
(vacuum)
• If there is sticking, replace the
EGR valve and check the fuel
injection system and the oil vapour
separator (blow-by separator)
• Especially for electric EGR valves,
check actuators and sensors
• Check the air mass sensor and
replace if necessary
• Check sensors and actuators
• If there is sticking, replace the
EGR valve and check the fuel
injection system and the oil vapour
separator (blow-by separator)
• Check the air mass sensor and
replace if necessary
DIAGNOSTIC TROUBLE
CODE
P0403 P0404 P0405 - P0408
DISPLAYED FAULTS EGR system – control loop
malfunction

EGR signals incorrect or implausible:
• Wear/soiling of the potentiometer
in the EGR valve, temperature
sensor
EGR System – control loop
measurement/power problem

• Exhaust gas recirculation outside
set-point range
• EGR signals incorrect or
implausible
• Wear/soiling of potentiometer in
the EGR valve, pressure sensor,
temperature sensor, air mass
sensor, electrical plug-in
connections and lines
EGR system – sensor A/B circuit too
small/large

• EGR signals incorrect or
implausible
• Wear/soiling of potentiometer in
the EGR valve, pressure sensor,
temperature sensor, air mass
sensor, electrical plug-in
connections and lines
NEXT STEPS/
POSSIBLE REMEDIES
• Check signals and compare with
set-point values
• Check signals and compare with
set-point values
• Check lines, plug-in connections
and components
• Check signals and compare with
set-point values
• Check lines, plug-in connections
and components