Cherokee 2WD L6-4.0L VIN S (1998)
* Ohms cannot be measured if voltage is present. Ohms can be measured only in a non-powered circuit.
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Voltage between any terminal and ground must not exceed 500v DC or 5C)0v peak AC.
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Use caution when measuring voltage above 25v DC or 25v AC.
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The circuit being tested must be protected by a 1 0A fuse or circuit breaker.
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Use the low current shunt to measure circuits up to 1 0A. Use the high current clamp to measure circuits exceeding 10A.
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When testing for the presence of voltage or current, make sure the meter is functioning correctly. Take a reading of a known voltage or current
before accepting a zero reading.
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When measuring current, connect the meter in series with the load.
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Disconnect the live test lead before disconnecting the common test lead.
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When using the meter function, keep the DRB away from spark plug or coil wires to avoid measuring error from outside interference.
Vehicle Preparation for Testing
Make sure the vehicle being tested has a fully charged battery. If it does not, false diagnostic error messages may occur.
Airbag System
Airbag System
A dual front airbag system is a standard equipment safety feature on this model. The airbag system is designed to provide increased driver and passenger
protection if the vehicle is involved in a front-end collision. A DRB III scan tool is required for diagnosis of the airbag system. The system is the most
effective when used in conjunction with the seat belt system. The airbag system consists of the Airbag Control Module (ACM), Instrument Cluster (IC),
driver and hybrid passenger airbag module, clock spring, data link connector and the Chrysler Collision Detection multiplex system (CCD bus). There
are no external impact sensors in this system.
The ACM is an electronic module that monitors the airbag system for proper operation, stores Diagnostic Trouble Codes (DTCs), controls the airbag
warning lamp, monitors the pressure in the passenger airbag module (1997 Model Year Only) and contains an energy storage capacitor. This capacitor
stores enough electrical energy to deploy the airbags for up to one second following a battery disconnect or failure during an impact. The purpose of the
capacitor is to provide airbag system protection in a severe secondary impact if the initial impact has damaged or disconnected the battery, but was not
severe enough to deploy the airbag.
The ACM is mounted on the floor of the vehicle, under the left front seat and a metal protective cover is the most visible part. The ACM provides DTCs
to the technician through the DRB III via the CCD bus. Some circuits are tested continuously; others are checked only under certain circumstances. The
Instrument Cluster (IC) turns the warning lamp on or off based on CCD bus messages from the ACM via the CCD bus. The ACM cannot be repaired and
must be replaced if it is damaged or faulty.
The airbag system is a sensitive, complex electromechanical unit. Before attempting to diagnose or service any airbag system or related steering wheel,
steering column or instrument panel components, you must first disconnect and isolate the battery negative (ground) cable Wait two minutes for the
system capacitor to discharge before further system service. This is the only sure way to disable the airbag system. Failure to do this could result in
accidental airbag deployment and possible personal injury.
Never strike or kick the airbag control module because it can damage the impact sensor or affect its calibration. If an airbag control module is
accidentally dropped during service, the module must be scrapped and replaced with a new unit.
The deceleration org-force resulting from the impact of a front-end collision causes the safing sensor inside the ACM to close. As soon as the ACM
internal accelerometer and the safing sensor are closed, an electrical charge is sent to the airbag module. This causes the inflator to be actuated, thus
deploying the airbags. The total time form the closure of the sensors to deployment and deflation of the airbags is 1/10 of one second.
The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. Whenever the ignition key
is turned to "run" or "start" position, the IC performs a lamp check by turning the AIRBAG warning lamp on for six to eight seconds. If after that the
lamp turns off, it means that the ACM has checked the system and found it to be free of discernible malfunctions. If the lamp remains on, there could be
an active fault in the system or the MIC lamp circuit may be defective. If the lamp comes on and stays on for a period longer than six to eight seconds
and then goes off, there is usually an intermittent problem in the system. The IC monitors the airbag warning lamp for an open or defective lamp driver
circuit. This information is sent to the ACM via a CCD bus message. The CCD bus messages listed below can be monitored using DRB III and selecting
"passive restraints," 'AIRBAG," "MONITOR DISPLAY" and "WARNING LAMP STATUS."
ACM LAMP REQUEST (on or off)
MIC BULB STATE (Ok or failed)
MIC DRIVER STATE (Ok or failed)
Perform the warning lamp circuit open procedure to find the cause of any customer complaint regarding the AIRBAG warning lamp, such as:
