3.0 SYSTEM DESCRIPTION AND
The body system on the 1999 WJ consists of a
combination of modules that communicate over the
PCI bus (Programmable Communication Interface
multiplex system). Through the PCI bus, information
about the operation of vehicle components and
circuits is relayed quickly to the appropriate module(
s). All modules receive all the information transmitted
on the bus even though a module may not
require all information to perform it’s function. It
will only respond to messages ‘‘addressed’’ to it
through a binary coding process. This method of
data transmission significantly reduces the complexity
of the wiring in the vehicle and the size of
wiring harnesses. All of the information about the
functioning of all the systems is organized, controlled,
and communicated by the PCI bus, which is
described in The Vehicle Communication Section of
this general information.
3.1 AIRBAG SYSTEM
The Airbag Control Module (ACM) is bolted to a
bracket on the floor panel transmission tunnel
rearward from the gear shift selector inside the
vehicle. The ACM mounting bracket is welded to
the tunnel and is not serviced with the ACM. The
ACM contains a microprocessor, the impact sensor,
and energy storage capacitor. The mircoprocessor
contains the airbag system logic. The ACM system
logic includes On-Board Diagnostics (OBD) capability,
and communicates with the instrument cluster
circuitry via the PCI data bus to control the airbag
The microprocessor in the ACM monitors the
impact sensor signal and the airbag system electrical
circuits to determine the system readiness. If
the ACM detects a monitored system fault, it sends
messages to the instrument cluster on the PCI data
bus to turn on the airbag indicator lamp. A preprogrammed
decision algorithm in the ACM microprocessor
determines when the deceleration rate as
signaled by the sensor indicates an impact that is
severe enough to require airbag system protection.
When the programmed conditions are met, the
ACM sends an electrical signal to deploy the airbag
The impact sensor is an accelerometer that
senses the rate of vehicle deceleration, which provides
verification of the direction and severity of an
impact. The impact sensor is calibrated for the
specific vehicle, and is only serviced as a unit with
the ACM. A mechanical sensor called the safing
sensor is also integral to the ACM.
The ACM also contains an energy-storage capacitor.
This capacitor stores enough electrical energy
to deploy the airbags, for 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 airbags.
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 COMPONENTSYOU
MUST FIRST DISCONNECTAND
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
NEVER STRIKE OR KICK THE AIRBAG
CONTROL MODULE, AS 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
The airbag warning lamp is the only point at
which the customer can observe ‘‘symptoms’’ of
system malfunction. Whenever the ignition key is
turned to the ‘‘run’’ or ‘‘start’’ position, the MIC
performs a lamp check by turning the airbag warning
lamp on for 6-8 seconds. If 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 internally
shorted to ground. If the lamp comes on and
stays on for a period longer than 6-8 seconds then
goes off, there is usually an intermittent problem in
Perform the WARNING LAMP OPEN procedure
in this book to find the cause of any customer
complaint regarding the AIRBAG warning lamp,
- warning lamp does not illuminate
- warning lamp stays illuminated with no active
The ACM cannot be repaired or adjusted and, if
damaged or faulty, it must be replaced.
SQUIB - also called initiator (located in rear
of airbag module)
DRIVER SQUIB CIRCUIT OPEN (ACTIVE)
When Monitored and Set Condition:
DRIVER SQUIB CIRCUIT OPEN (ACTIVE)
When Monitored: When the ignition is on, the ACM monitors the resistance of the Driver
Set Condition: The ACM has detected an open circuit or high resistance in the Driver
DRIVER AIRBAG LINE 2 OPEN
DRIVER AIRBAG LINE 1 OPEN
CLOCKSPRING DAB CIRCUITS OPEN
DRIVER AIRBAG MODULE OPEN
ACM, DRIVER AIRBAG CIRCUIT OPEN
Jeep Social Care Specialist
well the easy way to get the light off. Black tape over it...........
again the seat belt has a charge its at the bottom of the B pillar. The seats belts latch is only to tell the system if you have the belt on. it has two wire and is just a open or closed. to turn off the seat belt light just close the loop, open means belts are not on. nothing there to fix, its the other side that has the charge.
fact is many cars today get totaled after a crash as the these system can add a lot to a repair. the liability is huge as well. used parts are a no no. i would rather have a 5 point harness anyway.
I've got an '06 Commander, and had the airbag light stay on, but other stuff was acting up as well: Hvac panel inop, no compass readout, and the backup assist disable button all quit. The problem was a red 10 amp fuse in the under dash fuse box. Evidently, this small rated fuse controls relays that send the higher voltage where it has to go. So the fuses listed for the components could all check OK, yet the circuit does not work. The Commander manual has crap for explaining what the fuses do, so I did not know the component name for the fuse. The fuse was in the "stack" most inboard. Obtw, if you do go after those fuses on a Commander, the entire panel below the steering wheel is hinged, and opens like a glove box door. The factory flip open cover is a joke.
I've checked all the fuses below the dash and the ones under the hood. They all seem to be fine. Like I said I don't believe its the clock spring but I could be wrong. Right now I'm just wondering since I replaced that air bag should the light go off automatically or will it need to be reset now that the air bag has been replaced
"... the only thing that don't work on the steering wheel is the radio controls...."
This could indicate you have a circuit path open in that area. If your wheel has more than one circuit "track" on it, maybe one is not connecting anymore?
Find the circuit wires running to the driver airbag, and do a continuity check on the circuit from the airbag?
What I was getting at, is there might be more than one path on the steering wheel for the circuits to communicate with the computer modules. So if your radio contols do not work, that path or more could be out to lunch. I was suggesting that you pull the airbag connection at the wheel, and try a continuity test from there to the next junction in the wiring bundle. That will tell you if the system is "talking" to the airbag.
OK u lost me on the hole testing thing... I just bought this jeep 2 months ago and air bag light has been on since I got it. It has the factory radio in it but I have read something about if u put a after market radio in it that it could cause the air bag light to come on and also the radio controls ain't working so I'm wondering if maybe at one time if it maybe had a diff radio in it and a factory was put back and messed up the radio controls on the steering wheel and also causing the air bag light
Pulled the dash below the steering wheel to get a better look and I have 2 wires cut. Pink with black stripe and solid yellow. Any ideas where these should go to? There coming off the main connection going to the steering wheel there pointing down towards the floor and to the right off the fuse box
One thing you can do is look at the connection to the airbag, and compare that color code to the wires you found.
OBTW-if the car has to pass state inspection, you may be required to have everything up to standards before you can legally sell the vehicle. If so, the seller my be on the hook to get this fixed, or return your money.
Yea I've looked at the wires to the air bag and the steering wheel and not seeing the same color wires anywhere on it.. I no there coming off the main harness going up to the steering but I really don't think there going all up to the airbag . The wires are coming out the main harness right by the fuse box and going down towards the floor. Might be going to something under the hood or something not sure. But I would think since there wrapped seperate off the harness they go together but to what I don't no. Any ideas?
I just did some searching under "Air Bag" and a couple people with similar problems as yours fixed it this way:
Check the fuses marked "Spare" in the underhood fuse compartment. They are not extras to use, but are on a "spare" circuit. http://www.jeepforum.com/forum/f67/b...light-1211283/
I've checked under the hood and in the fuse box inside and all of the spare spots don't even have the clamps to hold a fuse. If u put one in it they would just fall out so I'm not sure that would work??