OBD-System
OBD and exhaust gas return system
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Information on diagnostics
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.
| 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
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 |