Description of On-Board Diagnostics

The diagnostic monitor assembly contains a microcomputer that monitors the electrical system components and connections. The monitor performs a self-check of the microcomputer internal circuits and energizes the system readiness indicator during prove out and whenever a fault occurs in the system. If certain faults occur, the system will be disarmed by a firing disarm device built into the monitor. If a system fault exists and the indicator is malfunctioning, an audible tone will be heard indicating the need for service.

The diagnostic monitor has a coded flashing indicator feature which assists the service technician in isolating a system malfunction or fault. The codes are produced by a series of air bag indicator flashes. Each flash is on for about one-half second and off for about one-half second. The number of flashes in each series is based on the type of fault being detected. The code (series of flashes) is repeated when the ignition switch is in the RUN position and a fault exists. The coded fault feature is prioritized that if two or more different faults occur at the same time, the highest priority fault indication will be shown until corrected.

NOTE: If a system fault exists and the indicator is malfunctioning, an audible tone will be heard indicating the need for service. The tone produced is a series of five sets of five beeps. The number of beeps does NOT indicate the fault code, it means the indicator is out and that a fault is present.

The faults and associated codes are listed in the Fault Code Priorities chart in the order that they are ranked from top to bottom. In other words, the fault (or code) at the top of the list has the highest priority (or ranking) and would be shown over any other code by the air bag indicator.

The fault (or code) at the bottom of the list has the lowest priority (or ranking). These listings are for information only and should not be used for system diagnosis or troubleshooting. The pinpoint charts Pinpoint Tests and deactivation procedure should be used to pinpoint the specific fault and to safely diagnose and service the system. However, if after using the diagnostic charts, the fault is not located, proceed to the diagnostic schematic to perform additional diagnostic checks to determine and correct uncommon faults.

FAULT CODE PRIORITIES

Number of Flashes Probable Fault
No Lamp In operative air bag indicator lamp circuit
continuous Light Diagnostic module disconnected or faulty
3 Loss of air bag deployment circuit power or backup power supply disconnected
5 Igniter circuit, or forward crash sensor deployment circuit shorted to ground
10 Faulty firing circuit disarm device
4 Potential short in air bag deployment circuit or improperly grounded dash panel sensor
6 Driver air bag circuit inoperative
7 Open monitor wiring circuit
8 Forward crash sensor improperly attached or grounded
9 Open forward crash sensor deployment circuit
2 All forward crash sensors disconnect
Tones 5 Sets of 5 Beeps Air bag lamp out and another fault

"Check Connection" means inspect connector for proper seating to mating connector, inspect terminals for good contact and inspect wiring for proper crimping to terminal.

All continuity checking is done with the system deactivated. This means that the driver air bag is disconnected and a jumper wire is installed.

"Disconnect" does not mean removal.

A disconnected part is not reconnected until specific reconnect instruction is given.

The following test equipment is used.
^ Rotunda Dwell-Tach-Volts-Ohms Tester 059-00010 or equivalent.
^ Jumper Wires.

NOTE: Attach positive (+) lead to circuit voltage and negative (-) lead to specified ground. (If a Digital Voltmeter is used on Circuit 608 with monitor disconnected, the readout will not indicate the correct voltage.)

All resistance checks must be made with the negative lead of the ohmmeter at vehicle ground, not battery ground, unless specifically directed otherwise. Three places are recommended: the metal bracket of starter relay, the ignition lock cylinder on the steering column or a ground wire from harness under instrument panel.

VERIFY AIR BAG INDICATOR means to turn the ignition switch to RUN and count the flashes only after the code(series of flashes) has cycled twice. If the air bag indicator comes on continuously for four to eight seconds and then goes out, the system is functioning properly and all faults have been serviced.