New Bosch coil design for BMWs has techs asking – Where’s the ‘snap’?

New redesigned coils for BMWs from Robert Bosch LLC, (part numbers 0 221 504 464/00124 and 0 221 504 407/00044), have had a number of automotive service technicians wondering what happened to the “snap.”

With the old design connector, a “snap” sound signaled that the coil had been properly installed, indicating that the job was complete and had been done correctly. Not so with the new redesigned coils, Bosch says. The absence of that sound has led some technicians to conclude that this may be a design fault that may cause the unit to fail prematurely and may result in engine misfires or other issues. Rest assured, that is not the case, the company notes.

Some technicians in the field believe that the coil was held in place by a connection between the contact bolt of the spark plug and contact inside the coil, and this “snap” sound must always be heard to indicate proper installation, Bosch says. In reality, the coil is held in two places: by the rubber boot that slips over the ceramic part of the spark plug, and by the sealing lips at the upper end of the coil.

With Bosch's new redesigned coil, the customary “snap” is no longer heard and it is not an indication that the coil has been properly installed. In fact, says the company, the new design provides better coil performance at the spark plug connection point which was the area that technicians expressed concern about.

New design coil with HV bush in coil and contact spring.	Old coil design with catch mechanism that produced the “snap” sound.

In other words, the original design actually gripped the spark plug tip and felt more secure whereas the new design uses a contact spring on the spark plug tip. This design may not feel like the connector is gripping the spark plug, but in reality, it does the job just as well, if not better than the old design.

Aesthetically, the change of the collar/housing around the coil body from a metallic to a plastic housing, and the spark plug connector, are obvious improvements for the appearance of this coil body and provides improvement in fit, form, and function as intended by BMW, Bosch says.

Bosch and BMW also have used this newer connector design in hundreds of thousands of OE (original equipment) BMW coils in recent years with no performance problems or other issues.