I have a 1999 f150 with a 4.2L that was wrecked, all of the work had been done, with the exception of the airbags and crash sensor reinstalled. I have the airbags back in and can not find where the front crash sensor is to mount, nor can I find the harness to plug it into. Can anyone provide a picture or diagram showing these?

 

As far as I can tell from the FORD manual there is no "front crash sensor". It's all contained in the Restraints control module (RCM) which is mounted on the trans hump under the dash. Didn't see one mounted on mine when I had the nose off. They were easy to spot on my '95 but nothing on the radiator support of my 98.


SECTION 501-20B: Occupant Restraints — Passive — Supplemental Air Bag System

1999 F-150/250 Workshop Manual
DESCRIPTION AND OPERATION
Procedure revision date: 02/03/1999
Air Bag Supplemental Restraint System (SRS)

The air bag supplemental restraint system (SRS) is designed to provide increased collision protection for front seat occupants in addition to that provided by the three-point safety belt system. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantages of the SRS.

The air bag supplemental restraint system (SRS) components are shown in the following illustration.


Air Bag Supplemental Restraint System (SRS) Components

Item Part Number Description
1 044A74 Passenger air bag module
2 14B268 Passenger air bag deactivation (PAD) switch
3 14B321 Restraints control module (RCM)
4 043B13 Driver air bag module
5 14A664 Air bag sliding contact

Air Bag Module — Driver

The driver air bag module:

* is replaced as an assembly.
* is mounted in the center of the steering wheel.

Driver Air Bag Module

Item Part Number Description
1 043B13 Driver air bag module
2 3600 Steering wheel
3 3F563 Steering wheel (Lightning)

Air Bag Sliding Contact

The air bag sliding contact:

* is mounted on the steering column, behind the steering wheel.
* continuously transfers electrical signals from the driver air bag module to the restraints control module (RCM).

Air Bag Module — Passenger

The passenger air bag module:

* is replaced as an assembly.
* is mounted in the RH side of the instrument panel.

Passenger Air Bag Module

Item Part Number Description
1 044A74 Passenger air bag module
2 04320 Instrument panel

Passenger Air Bag Deactivation (PAD) Switch

The passenger air bag deactivation (PAD) switch:

* is located on the instrument panel to the right of the climate controls.
* contains a light emitting diode (LED) that indicates when the PAD switch is activated (passenger air bag disabled).
* allows the passenger air bag deployment circuit to be disabled using the ignition key.
* should be used whenever a child safety seat is being used in the front passenger seating position.

Restraints Control Module (RCM)

The restraints control module (RCM) performs the following functions:

* signals the inflators to deploy the air bags in the event of a deployable crash.
* monitors the air bag supplemental restraint system (SRS) for faults.
* illuminates the air bag indicator if a fault is detected.
* flashes the air bag indicator to indicate the lamp fault code (LFC) detected.
* communicates through the data link connector (DLC) the current or historical diagnostic trouble codes (DTCs).
* signals the generic electronic module (GEM) to activate a chime if the air bag indicator is not available and another SRS fault exists.

NOTE: The safing sensor is internal to the RCM and is not serviced separately.

The RCM monitors the SRS for possible faults. If a fault is detected while the ignition switch is in the RUN position, the RCM will illuminate the air bag indicator located in the instrument cluster.

When the ignition is cycled (turned off and then on), the air bag indicator will remain lit for six seconds and then go out. If an SRS fault exists, the air bag indicator will then flash the two-digit LFC. The air bag indicator will flash the LFC five times, then it will remain illuminated for the rest of the key cycle. The RCM will also communicate the current and historical DTCs through the DLC, using the New Generation Star (NGS) Tester. If the air bag indicator does not function, and the system detects a fault condition, the RCM will signal the GEM to activate an audible chime. The chime is a series of five sets of five tone bursts. If the chime is heard, the SRS and the air bag indicator require repair.

LFCs are prioritized. If two or more faults occur at the same time, the fault having the highest priority will be displayed first. After that fault has been corrected, the next highest priority fault will be displayed.

The RCM includes a backup power supply. This feature provides sufficient backup power to deploy the air bags in the event that the ignition circuit is damaged in a collision before the safing and air bag sensors determine that an air bag deployment is required. The backup power supply will deplete its stored energy approximately one minute after the battery ground cable is disconnected.

Electrical System

The electrical system that supports the air bag supplemental restraint system (SRS):

* is powered from the battery through the ignition circuit.
* provides the electrical path from the restraints control module (RCM) to the air bag modules.
* provides the electrical path from the RCM to the air bag indicator.
* provides the electrical path from the RCM to the data link connector (DLC).
* provides the electrical path from the RCM to the generic electronic module (GEM).

Sensor

WARNING: The restraints control module (RCM) orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) has been involved in a collision in which the center tunnel area has been damaged, inspect the mounting and bracket for deformation. If damaged, the RCM must be replaced whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.

The SRS contains two sensors which are integral to the RCM. The RCM is mounted on the center tunnel under the instrument panel.

 

Behind the grille there are 2 small square boxes on each side that I assume are the air bag sensors. This of course was on my '97, don't know if they changed them in '99.

 

97-98 does show sensors, mounted to the inside of the frame rails. 99-up does not show these.

 

To correct that last post, the sensors on the 97-98 are mounted on a bracket on the radiator support.

 

The 99 does NOT use any external crash sensors. EVERYTHING is the RCM.

Steve

 

Seems like a step backwards to me. I do see how a minor wreck that caves the grille in could set off the air bags and total an otherwise fine truck but I'd still rather have the sensors in the crash area not in the middle of the truck somewhere. I got lucky in my wreck that they were not set off as the grille came close to caving into them.

 

Thanks guys, that would absolutely explain why I could find no plug in on the harness. The impact sensors that were laying in the truck must have been from the front clip that they used!

 

Does anyone know where the airbag diagnositc module is located on a '98 Expedition? I have an LFC 45. I checked continuity to ground on the LH crash sensor connector (P/LG wire) and had no resistance to the frame. I removed the sensor, cleaned the mounting area with a wire brush and re-installed for good measure, but did not eliminate the code. I would like to check the resistance to ground from the diagnostic module connector to check the entire circuit. Also , I noticed the sensor case was cracked and rusted, could this still set the code eventhough it electrically checks out? Where do I get another sensor beside the Stealer for $130?

 

The air bag diagnostic monitor is located behind the right kick panel. The OEM parts suppliers that are sponsors here show the front sensors to be in the $80 range. Check them out.

Pinpoint Test N: LFC 45/DTC B1945 — LH Air Bag Sensor Not Mounted to Vehicle Properly

Normal Operation

NOTE: Circuit 620 (P/LB) is riveted to the side of the LH air bag sensor case, and the case of the sensor is grounded to the vehicle at its mounting point.

The air bag diagnostic monitor measures the resistance between Pin C208-20, Circuit 620 (P/LB), and the reference ground at Pin C209-18, Circuit 649 (BK/O). If a difference of more than 3.0 ohms between the ground at Pin C209-18, Circuit 649 (BK/O), and the ground at Pin C208-20, Circuit 620 (P/LB) is measured, the air bag diagnostic monitor will store a diagnostic trouble code (DTC) B1945 in memory and flash a lamp fault code (LFC) 45 on the air bag indicator. Should the difference in resistance between Pin C209-18, Circuit 649 (BK/O), and Pin C208-20, Circuit 620 (P/LB), be repaired or otherwise reduced to less than 3.0 ohms, the air bag diagnostic monitor will store the DTC B1945 in memory.

Possible Causes

A high resistance reading on Pin C208-20, Circuit 620 (P/LB) or Pin C209-18, Circuit 649 (BK/O) can be caused by:

a poor attachment of LH air bag sensor and bracket due to loose mounting, dirt, or corrosion at its mounting location.
an open or damaged wire in Circuit 620 (P/LB).
an open wire or loose rivet inside LH air bag sensor and bracket.
a poor reference ground at Pin C208-10, Circuit 650 (BK/LB) or Pin C209-18, Circuit 649 (BK/O).

 

ncranchero:

Excellent information! On the way home from work Friday evening I noticed the light was no longer illuminated. I drove the vehicle about 500 miles this weekend and to work today with no LFCs. There must be a damaged wire or a bad ground somewhere. I guess I will have to wait for code to come back as its hard to fix problems that aren't currently problems. Thank for the info!

 

Electrical gremlins.............. Maybe they won't come back.