Dodge Nitro. Manual — part 253

Fig. 85: Identifying Sensor Mounting Flange, Threaded Mounting Stud, Stamped Metal Cage, Sensor
Body & Receptacle
Courtesy of CHRYSLER LLC

The seat weight sensors are strain gauge-type units. The electronic elements of the sensor are encased within the
sensor body (5) and the sensor body is located within a stamped metal cage (3). Four sensors are used in the
Occupant Classification System (OCS). The sensors are located below the seat cushion between the seat
adjuster track and the seat track riser at each corner of the passenger side front seat.

A threaded mounting stud (2) on each sensor body is secured by a nut to the seat track riser, and two nuts secure
each sensor mounting flange (1) to two studs integral to the front and rear of the inboard and outboard
passenger side lower seat adjuster tracks. A molded connector receptacle (4) integral to each sensor body is
oriented towards the center of the seat and is connected to the vehicle electrical system through a dedicated
connector and take out of the passenger seat wire harness beneath the seat cushion.

The seat weight sensors cannot be adjusted or repaired and, if ineffective or damaged, the entire sensor must be
replaced.

OPERATION

SEAT WEIGHT SENSOR

The seat weight sensor units are designed to sense the relative weight of a load applied to the passenger side
front seat, which provides a logic input to the microprocessor of the Occupant Classification Module (OCM).
When any load is applied to the seat the load is transmitted through the sensor mounting stud to the sensor body
(strain gauge) of each sensor, causing a change of electrical resistance through the strain gauge. These changes
in resistance within the internal sensor circuitry change the sensor output voltage.

Each weight sensor receives a nominal five volts and a ground through parallel hard wired circuits from the
OCM. The OCM then monitors the output voltage of each sensor on dedicated hard wired data communication
circuits. The OCM also monitors the condition of the sensor circuits and will store a Diagnostic Trouble Code
(DTC) for any fault that is detected, then send messages to the Occupant Restraint Controller (ORC) to
illuminate the airbag indicator in the Electro Mechanical Instrument Cluster (EMIC) (also known as the Cab

2007 Dodge Nitro R/T

2007 RESTRAINTS Service Information - Nitro

Compartment Node/CCN).

The hard wired circuits between the seat weight sensor and the OCM may be diagnosed using conventional
diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic
methods will not prove conclusive in the diagnosis of the seat weight sensors or the electronic controls and
communication between other modules and devices that provide features of the Occupant Classification System
(OCS). The most reliable, efficient, and accurate means to diagnose the seat weight sensors or the electronic
controls and communication related to seat weight sensor operation requires the use of a diagnostic scan tool.
Refer to the appropriate diagnostic information.

REMOVAL

SEAT WEIGHT SENSOR

WARNING:

To avoid serious or fatal injury on vehicles equipped with airbags, disable
the Supplemental Restraint System (SRS) before attempting any steering
wheel, steering column, airbag, Occupant Classification System (OCS),
seat belt tensioner, impact sensor, or instrument panel component
diagnosis or service. Disconnect and isolate the battery negative (ground)
cable, then wait two minutes for the system capacitor to discharge before
performing further diagnosis or service. This is the only sure way to
disable the SRS. Failure to take the proper precautions could result in
accidental airbag deployment.

WARNING:

To avoid serious or fatal injury on vehicles equipped with the Occupant
Classification System (OCS), do not modify the front passenger seat
assembly or center floor console in any way. Do not use any prior year,
subsequent year, secondary or aftermarket seat trim covers. At no time
should any Supplemental Restraint System (SRS) or OCS component be
modified or replaced with any part except those which are specified for
the particular vehicle application . Failure to observe these precautions
could cause an OCS miscalibration condition, which may result in the
passenger airbag failing to deploy when required or deploying when not
required.

WARNING:

To avoid serious or fatal injury, never strike or drop a seat weight sensor
or the passenger side front seat assembly to which the sensors are
secured as it can damage the sensors or affect their calibration. The seat
weight sensors and the passenger side front seat assembly must be
handled with care to avoid damage to the sensors. Do not sit upon or
place any loads upon a passenger side front seat while it is removed from
its mounts in or outside of the vehicle. If an individual sensor is dropped
or damaged, replace the sensor with a new and unused unit. If a seat has
been dropped during removal or loaded while removed from its mounts,
replace each of the seat weight sensors with new and unused units.
Failure to observe this warning could result in an accidental, incomplete,

2007 Dodge Nitro R/T

2007 RESTRAINTS Service Information - Nitro

Fig. 86: Strain Gauge Alignment Tool (Special Tool No. 9689) Used To Secure Body Of Seat Weight
Sensor
Courtesy of CHRYSLER LLC

1. Disconnect and isolate the battery negative cable. Wait two minutes for the system capacitor to discharge

before further service.

2. Remove the passenger side front seat from the vehicle. Refer to REMOVAL .

3. From the underside of the seat, disconnect the seat wire harness from the connector receptacles of each of

the four weight sensors.

4. Disconnect the seat wire harness from the connector receptacle of the seat track position sensor located on

the inboard side of the inboard seat adjuster upper track near the rear of the seat track.

or improper passenger side front supplemental restraint deployment.

CAUTION: A strain gauge alignment tool (Special Tool No. 9689) (2) must be

used to secure the body of the seat weight sensor (1) from any
rotation during removal or installation of the nut that secures the
sensor stud to the seat track riser. In addition, the sensor fasteners
should always be serviced using hand tools ONLY, and not electric
or pneumatic power tools. Failure to observe these cautions may
result in irreversible sensor damage requiring sensor replacement.

2007 Dodge Nitro R/T

2007 RESTRAINTS Service Information - Nitro

Fig. 87: Identifying Center Fork & Tool Support Yoke
Courtesy of CHRYSLER LLC

5. Install the strain gauge alignment tool (Special Tool 9689) on the sensors by inserting the center fork (1)

of the tool between the flats on each side of the sensor body and inside of the cage, then seating the tool
support yoke (2) firmly against the outside of the sensor cage.

2007 Dodge Nitro R/T

2007 RESTRAINTS Service Information - Nitro