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Peugeot 308: The hidden SCR cat
A family on vacation in a two-year-old PEUGEOT 308 has painful experiences with the complexity of exhaust gas purification systems installed in French diesel vehicles.
Peugeot 308: The hidden SCR cat
The Peugeot 308 is powered by a 2.0 Blue HDi diesel engine and only has 55,000 km under its belt. It's no wonder that the sudden error message is quite unexpected. The warning appears in orange letters on the display: “Emission reduction error: Starting prohibited after 600 km”. A visit to the workshop is unavoidable and the planned vacation trip has to be postponed for now. Unfortunately, the assumption that only one additive container needs to be refilled turns out to be a mistake. A diagnostic crime thriller begins.
TROUBLESHOOTING IN DETAIL
▶ The workshop technician checks the small plastic tank for the additive EOLYS 176, which Peugeot uses for the particularly efficient regeneration of the FAP soot filter in its diesel vehicles. This shows that the container is still more than half full.
▶ A visual inspection of the exhaust aftertreatment system with Oxi-Kat and FAP also shows nothing unusual. A “mega macs” diagnostic device is connected and it turns out that there are two errors stored in the control unit: P20E8, “Urea additive pressure sensor – signal too low” and P20F9, “Additive injection valve bank 1 – system stuck – constantly open”.
▶ The wording “urea” puzzles the master because at first glance he cannot see a second additive tank for AdBlue to reduce nitrogen oxides. In fact, one can be found in the mega mac's vehicle-specific list.
▶ A closer examination of the exhaust system shows: A three-part system consisting of Oxi-Kat, SCR and FAP is actually installed in the Peugeot 308 Euro 6. The problem: SCR and FAP cannot be separated by the mechanic. The hidden SCR catalytic converter only reveals itself through an additional heated line.
▶ According to the service booklet, the Ad Blue tank was last filled around 5,000 km ago. Since one filling is usually sufficient for around 20,000 km, the suspicion of a leak in the AdBlue system arises. A visual inspection of the heated line between the tank and the injection valve behind the Oxi-Kat close to the engine shows negative results.
▶ Pressurization using a supply pump should show more, the AdBlue injection valve from the exhaust pipe is dismantled. The electrical interface is disconnected to prevent the valve from being activated during the pressure test.
▶ In the menu item Diagnosis>Engine>Actuator>Test exhaust gas purification system in the mega macs, “Check urea injection valve” is selected. The supply pump is then activated - with a positive result: the obvious drop formation reveals the leaky injection valve.
▶ The valve is replaced, the AdBlue tank is filled and the system is vented. Conclusion: problem solved, case solved.
PETER SEIPEL COMPLEX DIESEL CLEANING
In order for modern diesel vehicles to be able to adorn themselves with the Euro 6 label, they carry around complex exhaust gas purification systems. The soot filter in the Peugeot 308 is regularly burned free using post-injection and the addition of a cerium additive. An SCR catalytic converter is also integrated in the same sheet metal casing behind the Oxi-Kat and directly in front of the FAP. Since the AdBlue solution freezes at -11 °C, the pipes and storage tank in the vehicle must be heated. A pump ensures a constant supply to the injection valve in front of the SCR catalytic converter as well as the backflow of urea after the ignition is switched off. The engine management controls the dosage of the additive depending on the exhaust gas mass flow and the signal from the NOx sensor behind the SCR catalytic converter. A highly complex system that naturally also harbors numerous sources of error. This is not inconvenient for car dealerships, as they earn significantly more from maintaining and repairing a vehicle than from selling it.