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BMW N51, N52, N54, N55 6-Cylinder Sepentine Belt Failure and Power Steering Pulley Hitting Subframe

Mar 18 16

A Serpent In My BMW/MINI?

Most BMWs from the early ’90s-on and all MINIs employ the now common, serpentine type accessory drive belt systems.  In deference to the older (classic) multiple V-belt system, with each belt commonly used to drive  a single engine accessory (alternator, water pump, power steering, air conditioning), the serpentine system uses a single long belt to drive multiple engine accessories.  As the serpentine drive system wears, it is not uncommon to begin to hear squeaking, squealing or other belt and/or pulley related sounds, indicating replacement time is near.  It is far more preferable to preventatively replace the belt and pulleys prior to failure.  A failed pulley or belt will, at a minimum, put the vehicle out of commission.  However, as the belt derails from the pulleys, it may cause other damage as it wraps and entwines itself around the various accessories at the front of the engine.  Not only is this a mess to take care of, but it may also cost more to repair due to the incidental damages from the flailing belt.

How Do I Prevent Belt Failure?

Our common recommended interval for preventative serpentine belt and pulley replacement is 80,000 to 100,000 miles.  On the late model BMW “N” family 6-cylinder engines (N51, N52, N54, N55), we recommend 60,000 mile belt and pulley replacement, or sooner, if inspection shows ANY belt or pulley wear.

Here’s why:

The N-series engines add a bit of urgency to the belt and pulley preventative replacement idea.  Unlike other BMW engines, these engines do not have a balancer wheel between the crankshaft pulley (the serpentine belt drive pulley) and the engine’s timing cover.  This can allow an errant belt (one that has come apart or is being derailed by a failing pulley) to slip between the pulley and the timing cover, to the crankshaft hub and oil seal.  At a minimum, the oil seal can be damaged.  However, it is not uncommon for the belt to be “sucked” into the timing cover, past the oil seal, and into the timing chain.  If this happens, the timing chain will derail and cause the camshafts to become “untimed”, likely causing valve to piston contact and catastrophic engine damage.


When used in the E90/91/92/93 3-series chassis, the N-series engines can experience contact between the power steering pulley and the engine sub-frame.  This can damage the pulley and/or the belt, resulting in the scenarios noted above.  Therefore, additional detail in belt and pulley inspection is called for on these models.

BavAuto prefers and recommends the CRP (Continental Rubber Products) replacement serpentine belts and belt/pulley replacement kits (everything you need in one box).  The pulleys in the CRP replacement kits are manufactured by INA, the original BMW manufacturer.

Click below for Serpentine belts, pulleys and kits:

Check out this CRP video supporting and explaining the serpentine problems on the N-series 6-cylinder engines:

Bavarian Autosport

BMW DIY Video – Replacing 3-Series Heat and AC Blower Motor and or Final Stage Resistor – E90, E82, E84, F25, E89, F26

Jan 29 16

Back in the Fall 2015 Fast Times (Click HERE for this article), we talked about the common faults and issues with the later model climate control (heat & A/C) blower motor speed controls, or final stage units (such as the blower not functioning, or not being consistently and properly controlled).  See the prior article (link in prior sentence) for a full description of the symptoms that may indicate a blower motor or final stage fault.

Starting with the mid ’00 and later, 1, 3, X1, X3 and Z4 models, the blower motor and the final stage unit are redesigned and mounted in a fully different manner and location.  Both the blower motor and the final stage unit are mounted forward of the glovebox, making them relatively easy to service.  This DIY video will address these models.  The prior article showed the replacement of the final stage unit as used in the 3, 5, Z4 and X models from the mid ‘90s through the mid ‘00s.

In this DIY we will be replacing the blower motor and final stage unit in a 2007 E90 335i.  The final stage location and the general procedures shown will be very similar for many BMW models, including; E82/88 1-series 2008-13, E90/91/92/93 3-series 2006-11, E84 X1 2013-15, F25 X3 2009-15, F26 X4 2014-on, E89 Z4 2009-15. The Bentley repair manuals (where available) detail the final stage unit location and replacement procedures for the different models.


Blower motor:

Final Stage Resistor Unit:


BavAuto® Metric socket, torx & allen tool set:

BavAuto non-marring pry tool set:


1)   Remove the lower trim panel, forward of the glovebox.  Remove the two Torx screws and pull the panel to the rear and downward.

2)  Remove the auxiliary outlet socket and  footwell light harness plugs.

3)  Remove the footwell air duct.  Pull the end of the duct downward to release from the clip.

Pull the opposite end of the duct from the main air distribution housing.

4)  Disconnect the vehicle wiring harness plug from the final stage unit.

5)  Locate the blower motor locking tab on the forward side of the blower motor mounting flange.  Press the tab downward and turn the motor counter-clockwise.

6)  Lower and remove the motor and final stage assembly.

7)  Disconnect the blower motor harness plug from the final stage unit.

8)  Remove the two Torx screws securing the final stage unit to the blower motor housing.

9)  Assemble the new blower or final stage unit to the corresponding original unit or assemble both a new blower motor and final stage unit using the original securing screws.

10) Connect the blower motor harness plug to the final stage unit.

11) Install the blower and final stage assembly into the vehicle blower housing, noting the position of the locking tab.  Position the motor in the housing and turn clockwise to lock.

12) Connect the vehicle harness plug to the final stage unit.

13) Install the lower trim panel.


BMW DIY Video – Replacing Rear Brake Pads & Rotors on Models with Electric Parking or Emergency Brake

Jan 29 16

You’ve likely seen our DIY video on replacing brake pads and rotors on a typical BMW or MINI (if not, watch it HERE).  The video shows how easy it is to replace the front and rear brake pads and rotors, without paying a shop a few hundred dollars.  Since the video was published, BMW has introduced electric parking brake systems on many of the newer and current models. While the front brake renewal procedures have not changed, the procedures for replacing the rear pads is unique, due to the addition of the electric parking brake system.  There are currently two different electric parking brake systems.  The first generation system uses an electrical actuator that activates cables to standard drum-style parking brake assemblies.  The second generation system uses electric actuators directly on the brake calipers.

Here are the links to our other brake service videos and DIYs:

Click HERE for front & rear brake pad & rotor replacement on most BMWs

Click HERE for Brake pad replacement on later model BMWs with new-style anti-rattle clips and caliper mounts

As noted above, the second generation electric parking brake system incorporates an electric motor driven caliper piston extender mechanism that mechanically extends the brake caliper piston to compress the pads against the brake rotor (as opposed to a separate small cable actuated drum brake assembly inside the brake rotor’s hub, or hat).  Unlike a standard brake caliper, the piston cannot be simply pushed back into the caliper, using a piston compressor tool.  According to BMW, the pistons must be retracted through use of the BMW factory scan/diagnostic tool.  The tool is connected to the vehicle’s diagnostic port and then programmed to retract the pistons through the parking brake motor actuators.  Once the parking brake piston extenders are retracted, the standard brake pad replacement can proceed.

So, you ask, do I have to take my vehicle to the BMW dealer for rear brake service?  No.

As a DIY BMW owner, there are two options in servicing the rear brakes.  We can use an aftermarket fault code and scan tool (available from or we can manually retract the actuators by performing a bit more work.

Click below for Universal OBD-II Fault Code & Diagnostic Tool with electric parking brake service function:

In this DIY video, we’ll show you how to circumvent the BMW parking brake retractor program and perform your rear brake service at home.  Follow along as we read more…