Is your alarm going off randomly? In most cases, your culprit is a small hood security switch in the engine bay that takes no more than a few minutes to replace!
Depending on which BMW model you own, you may have a ‘clown nose’ red light on your rear-view mirror. When you lock your car, this light should flash, every ~3 seconds or so. If the car thinks there is a fault in the alarm system (hood sensor failure) the light will flash rapidly, maybe 2 times per second or more immediately after locking.
Objective: Replace hood sensor switch to stop alarm from randomly sounding.
Applicable Vehicles:
1996-2002 BMW E36 Z3-series.
1999-2006 BMW E46 3-series: 323i, 325i, 328i, 330i, M3.
2004-2010 BMW E83 X3-series.
2007-2012 BMW E9x 3-series: 325i, 328i, 330i, 335i, M3.
1996-2003 BMW E39 5-series: 523i, 525i, 528i, 530i, 535i, 540i, M5.
2000-2006 BMW E53 X5-series.
2004-2010 BMW E60 5-series: 525i, 528i, 530i, 535i, 545i, 550i, M5.
2003-2010 BMW E63/4 6-series: 640i, 650i, M6.
1994-2001 BMW E38 7-series: 740i, 740iL, 750iL.
2001-2008 BMW E65 7-series: 745i, 745Li, 750i, 750Li, 760Li, B7.
Part Required:
Hood Sensor Switch: 61319119057
Cost: $45
Difficulty: Extremely Low
Time Required: Two minutes.
Procedure: The hood switch is located close to the firewall under the hood. On an E39 5-series, it’s on the cabin air filter housing on the driver’s side (top photo in this article of E39 M5, white circle outlines sensor.) Once you’ve located the switch, depress a tab on the electrical connector and unplug it. Next, squeeze the sides of the sensor and rotate it free from the air filter housing. Carefully press the new part in, and connect the electrical harness.
Hood sensor close-up. Note that the electrical wire should run behind but stud on the strut tower that the cabin box mounts to, not as pictured above.
E39Source Hood Sensor and Cabin Box Replacement DIY