21 November 2005

Detroit Diesel Corporation (DDC) has issued a recall for approximately 1,250 urban transit buses which experienced problems with plugging of diesel particulate filters (DPF) and turbocharger defects. The affected DDC Series 50 urban bus engines will receive new diesel particulate filters and/or new turbochargers at no cost to the users.

The recall applies to 2001-2004 model year (MY) DDC Series 50, 8.5 liter, 275 and 330 hp urban bus diesel engines. 257 2001 and 2002 MY 330 hp engines will receive turbocharger replacements. 584 2003 and 2004 MY 330 hp engines will receive both diesel particulate filter and turbocharger replacements. 409 2003 and 2004 MY 275 hp engines will receive new particulate filters.

The compressor wheel and turbine wheel of the defective turbochargers experienced fatigue failures. They will be replaced with the most current, improved version.

The DPFs failed to regenerate and plugged with particulate matter, thus requiring frequent cleaning to remove the accumulated soot. They will be replaced with a new particulate filter designed to minimize soot accumulation (presumably coated with a more active catalyst and/or higher catalyst loading).

The US Environmental Protection Agency (EPA) said it discovered these bus engine problems through transit bus fleet manager complaints, emission related defect reports, and through discussions with DDC. After DDC performed a series of tests on the improved particulate filters and filed completed emission related defect reports, EPA agreed to DDC’s recall campaign.

The DPF system available as an option on the affected urban buses utilized passively regenerated catalyzed particulate filter. The regeneration of the filter was dependant on the exhaust gas temperature, thus a risk of filter plugging existed during prolonged operation at light engine loads. DPF systems that will be introduced on US 2007 MY engines will rely on active regeneration, where the exhaust gas temperature will be increased by injection and catalytic combustion of diesel fuel in the exhaust system.

Source: US EPA (press release | recall page)