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Pelican Technical Article:

Airbag System Overview

Nick Czerula

Time:

1 hour1 hr

Tab:

$1000

Talent:

*****

Tools:

Tool set, MINI Scan tool

Applicable Models:

R52 MINI Cooper Convertible (2007-08)
R52 MINI Cooper S Convertible (2007-08)
R56 MINI Cooper Hatchback (2007-11)
R56 MINI Cooper S Hatchback (2007-11)
R57 MINI Cooper Convertible (2009-11)
R57 MINI Cooper S Convertible (2009-11)

Parts Required:

Airbag parts

Hot Tip:

Disconnect battery and wait 15 minutes before working on airbags

Performance Gain:

Remedy fault codes

Complementary Modification:

Replace cabin air filter

MINI R56 Supplemental Restraint System (SRS)

MINI R56 models [R55 (Clubman), R56 (Coupe), R57 (Convertible)] are equipped with the MINI Multiple Restraint System (SRS), consisting of airbags and seatbelt for passenger safety. The MRS system detects accident situations and, depending on the severity of the crash, deploys various components in the restraint system to protect vehicle occupants from injury.

The safety equipment consists of:

Two-stage driver airbag in the steering wheel.

Two-stage passenger airbag on the right side of the dashboard.

Side airbags secured to the outboard edge of front seat backrests and covered by the upholstery.

Curtain airbags along the entire side of the vehicle above the doors.

Pyrotechnic (explosive charge) seat belt buckles, which tension seat belts an additional two inches in caser of a crash.

Software in the MRS control module processes input from the following sensors to determine the direction and severity of a crash:

MRS control module contains two acceleration sensors at right angles to each other; sensors measure longitudinal (fore-aft) and transverse (side-to-side) acceleration (or deceleration).

B-pillar satellite crash sensors also contains two acceleration sensors each, one longitudinal and the other transverse.

Door pressure sensors detect sudden increase of air pressure in the door cavity. Signals from these sensors are used to verify the plausibility of the crash sensor signals during a side-crash (T-bone) event.

US models only: Acceleration sensors behind the headlights detect longitudinal acceleration.

The MRS control module, located underneath the center console behind the shifter, needs input from two independent sensors to determine that a crash has occurred. Triggering algorithms in the software determine crash severity and direction and fire seat belt tensioners and airbags in a programmed sequence. Additional sensors and switches also supply information to the control module:

The passenger seat occupancy sensor (OC3) detects the presence of a passenger or child seat. The sensor is also capable of deducing the mass of the passenger. The passenger side airbag is prevented from deploying in case of a very small person or child seat being in the passenger seat. A "Passenger airbag OFF" warning light illuminates next to the headliner switch module.

The front seat belt buckle micro switches detect whether the seat belts are buckled. This information is used to modify the deployment of airbags.

US models only: The driver seat position sensor detects the size of the driver. The two-stage airbag deployment strategy is modified to correspond to the size of the driver.

Diagnosis

When the ignition is first switched ON, the SRS module goes through a three- to five-second system-check during which the airbag warning light is illuminated. If no faults are detected, the airbag light switches OFF, indicating that the system is operative. If faults are detected, the driver is warned because the warning light stays ON. If the warning light is illuminated, the airbag system is inoperative and the airbags will not deploy.

The control module stores detected faults. You may read stored faults using a MINI-compatible scan tool. Once repairs are made, a scan tool is once more necessary to clear the stored fault codes. Because of the complexity of the MRS system, diagnosis and repairs to the system may be complicated and expensive. Below is a brief discussion of some of the likeliest causes of MRS failures.

One frequent source of MRS problems is with the control module itself. Perhaps because it is located under the center console, its terminals may get damaged by spilled drinks or possibly by moisture from the vehicle floor. In any case, there are a number of cases where inspection of the module connectors has revealed corrosion.

Another source of problems is malfunction of the passenger seat occupancy sensor. This is a pad underneath the seat upholstery. When it malfunctions the passenger airbag becomes inoperative.

Connectors underneath the front seats transmit electrical signals to the seat-back mounted side airbags. If a connector is disturbed, for example during an interior cleaning or for some other reason, the airbag system goes into warning mode.

The clock spring, an electrical contact at the base of the steering wheel connecting the horn and the driver airbag to the vehicle electrical system, can become over-twisted and break due to careless repairs to the steering wheel or other steering system components, or simply due to wear and tear.

Yet another possible problem: One of the airbags may be defective.

Repairs to the airbag system are often costly due to the expense of parts and the need for reliability and safety. If your airbag warning light is illuminated, it is best to let a professional with the right kind of scan tool and knowledge of the system diagnose and repair the problem.

One frequent source of MRS problems is with the control module (red arrow) itself.
Figure 1

One frequent source of MRS problems is with the control module (red arrow) itself. Perhaps because it is located under the center console, its terminals may get damaged by spilled drinks or possibly by moisture from the vehicle floor. In any case, there are a number of cases where inspection of the module connectors has revealed corrosion.

Another source of problems is the malfunction of the passenger seat occupancy sensor.
Figure 2

Another source of problems is the malfunction of the passenger seat occupancy sensor. This is a pad underneath the seat upholstery. When it malfunctions the passenger airbag becomes inoperative. This photo shows an occupancy mat from a similar model (red arrow)

The clock spring (red arrow), an electrical contact at the base of the steering wheel connecting the horn and the driver airbag to the vehicle electrical system, can become over-twisted and break due to careless repairs to the steering wheel or other steering system components, or simply due to wear and tear.
Figure 3

The clock spring (red arrow), an electrical contact at the base of the steering wheel connecting the horn and the driver airbag to the vehicle electrical system, can become over-twisted and break due to careless repairs to the steering wheel or other steering system components, or simply due to wear and tear.


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Comments and Suggestions:
OzCop Comments: I took my car to a car wash, something I rarely do, and there was no air bag light lit at that time...When I retrieved my car and started the engine, the air bag light did not go off and has been on for a couple of weeks...any suggestions? I'm assuming we are looking at the bottom side of the passenger seat in this particular photo.
November 8, 2016
  Followup from the Pelican Staff: Was it detailed? If the passenger seat was kneeled on. the seat mat may have been damaged (if it was worn). You'll need to check for fault codes.- Nick at Pelican Parts  

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