Chart No.10 Sys. Disarm Failure DTC B1924/B1342 LFC 24

System Disarm Failure Or Internal Diagnostic Monitor Fault (DTC B1924/B1342, LFC 24) Normal Operation

When the diagnostic monitor detects a LFC 13 or 14 (DTC B1913 or B1914) failure, it attempts to disarm the air bag system to prevent inadvertent deployment of the air bag(s) by blowing the 10A battery fuse (Mini-fuse #16 - engine compartment) feeding diagnostic monitor Pins 5 (R/W) and 6 (R/W) at the gray connector. It attempts to blow the fuse by activating an internal solid state switch which shorts the battery feed at Pin 6 (R/W) to sheet metal ground at the diagnostic monitor bracket.

WARNING: Under no circumstances should another fuse value be substituted for the 10A battery fuse. Any fuse other than 10A may cause disarming failure and may result in danger to the occupants of the vehicle. Do not attempt to replace the 10A battery fuse unless the air bag system first has been deactivated.

The air bag diagnostic monitor will make up to three attempts to blow this fuse, spaced at one minute intervals.
^ If the air bag diagnostic monitor has blown the fuse and thus removed battery voltage at Pin 5 (R/W) of the gray connector, DTC B1867 will be stored.
^ If the air bag diagnostic monitor attempts to blow the 10A battery fuse (Mini-fuse #16 - Engine compartment) three times and fails each time, DTC B1924 will be stored.
^ After the 10A fuse is blown or three attempts to blow it fail, the air bag diagnostic monitor will not attempt to disarm again until (DTCs B1913 or B1924) condition has been serviced and cleared.

The air bag diagnostic monitor also performs several self tests every time the ignition switch is turned to ON.
^ If any of these tests fail, the air bag diagnostic monitor will flash LFC 24.
^ If any of these conditions later resumes normal operation, LFC 24 (B1924) will be stored in background memory.

For NGS Tester-based diagnosis, the failure will generate either a DTC B1924 or B1342 depending on the cause of the failure. DTC B1342 is a special case DTC that will only be retrieved as a result of running the ON-DEMAND SELF TEST. An intermittent B1342 cannot exist due to this fact. This DTC indicates that an internal microprocessor fault exists in the diagnostic monitor. DTC B1924 covers the other internal diagnostic monitor faults described above and is handled like any other DTC.

Possible Causes
System disarm failure or internal diagnostic failure can be caused by:
^ Resistance to ground in the normally open primary crash sensor feed circuits - (P/O, P/W, Y/W, Y/LG).
^ An improper fuse value in the battery circuit feeding air bag diagnostic monitor Pins 6 (R/W) and 5 (R/W) at gray connector.
^ Excessive resistance or opens in the battery feed circuit due to corrosion, poor crimps, etc. The excess resistance could occur in the wiring at the air bag diagnostic monitor harness Pin 6 at gray connector, the 10A battery fuse terminal (Mini-fuse #19 - Engine compartment), or elsewhere in the battery feed circuit.
^ A vehicle charging system concern could prevent the air bag diagnostic monitor from drawing enough current to perform its disarm.
^ An internal air bag diagnostic monitor failure on self test or system disarm.

Electrical Schematic - System Disarm Failure Or Internal Diagnostic Monitor Fault:

Electrical Schematic - System Disarm Failure Or Internal Diagnostic Monitor Fault

Step 1
Check it diagnostic monitor is communicating.
1. Connect NGS Tester to DLC under steering wheel.

Step 1:

2. Did monitor communicate?

Step 2
Check if fault is hard or intermittent.

Step 2:

1. Using NGS Tester, run ON-DEMAND SELF TEST.

Step 2:

2. Did monitor respond with DTC B1924 or B1342?

Step 3
Check if fault is diagnostic monitor failure.

Step 3:

1. Did monitor respond with DTC B1342?

Step 4:

Step 4
Check primary crash sensor feeds.
1. Deactivate system. Refer to Deactivation Procedure.
2. Disconnect air bag diagnostic monitor.
3. Measure resistance from Pins 4 (P/N - gray connector) and 2 (Y/LG - black connector) to Pin 1 (B/W) of gray connector.
4. Measure resistance from Pins 3 (P/O - gray connector) and 1 (Y/W - black connector) to Pin 1 (B/W) of gray connector.

Step 4:

5. Are resistance readings infinite (open)?

Step 5
Determine if sensor or wire is shorted.
1. Disconnect primary crash sensor corresponding with the resistance to ground found in Step 4.

Step 5:

2. Measure resistance across the normally open contacts of the primary crash sensor.

Step 5:

3. Is resistance reading infinite (open)?

Step 6
Check for shorted sensor circuit.
1. Disconnect air bag diagnostic monitor.
2. Measure resistance between Pin 4 (P/W) of gray connector and known good ground.

Step 6:

3. Is resistance less than 1,000 Kohms?

Step 7
Check for incorrect wiring.
1. Examine air bag diagnostic monitor harness connector Pin 3 at black connector. Pin 3 should not be connected.

Step 7:

2. Is a wire connected to Pin 3?

Step 8
Check if repaired.
1. Deactivate system. Refer to Deactivation Procedure.

Step 8:

2. Has a DTC B1924/B1342 just been serviced and repaired?

Step 9
Check primary sensor feeds.
1. Deactivate system. Refer to Deactivation Procedure.
2. Disconnect diagnostic monitor.
3. Measure resistance from Pin 4 (P/W) of gray connector and Pin 2 (Y/LG) of black connector to Pin 1 (B/W) of gray connector.
4. Measure resistance from Pin 3 (P/O) gray connector and Pin 2 (Y/LG) black connector to Pin 1 (B/W) of gray connector.

Step 9:

5. Are resistance readings infinite (open)?

Step 10
Determine if sensor or wire is shorted.
1. Disconnect primary crash sensor corresponding to the shorted circuit with resistance to ground found in Step 9.
2. Measure resistance across normally open contacts of primary crash sensor at the sensor connector.

Step 10:

3. Is resistance reading infinite (open)?

Step 11
Check for shorted sensor circuit.
1. Disconnect air bag diagnostic monitor.
2. Measure resistance between Pin 4 (P/W) of gray connector and known good ground.

Step 11:

3. Is resistance less than 1,000 Kohms?

Step 12
Confirm battery condition.
1. Deactivate system. Refer to Deactivation Procedure.
2. Disconnect diagnostic monitor.

Step 12:

3. Measure voltage between Pin 6 (R/W) of gray connector and Pin 1 (B/W) of gray connector.

Step 12:

4. Is voltage measured equal to charging system voltage?

Step 13
Check fuse.
1. Inspect 10A battery fuse feeding diagnostic monitor Pins 5 (R/W) and 6 (R/W) of the gray connector.

Step 13:

2. Is fuse value correct?

WARNING: Certain fault conditions (DTCs B1913 and B1914, LFCs 13/53 and 14/54) may cause the diagnostic monitor to intentionally blow the 10A battery fuse (Mini-fuse #19--engine compartment box) to disarm the air bag system. DO NOT SUBSTITUTE ANOTHER FUSE VALUE FOR THE 10A BATTERY FUSE. Another fuse value may cause future disarming failure and may result in danger to the occupants of the vehicle. Once the diagnostic monitor has disarmed the system, it will not attempt to do so again until the appropriate fault code (DTCs B1913 and B1914, LFCs 13/53 and 14/54) has been cleared. DO NOT REACTIVATE SYSTEM UNTIL ALL FAULT CODES HAVE BEEN CLEARED.

Step 14
Check for short to battery.

Step 14:

1. Remove 10A battery fuse (Mini-fuse #19-engine compartment) feeding air bag diagnostic monitor gray connector Pins 5 (R/W) and 6 (R/W).
2. Measure voltage between Pin 6 (R/W) and Pin 1 (B/W) of gray connector.

Step 14:

3. Is voltage reading zero?

Step 15
Check for other DTCs.

NOTE: Do not clear DTCs until all DTCs have been addressed.

Step 15:

1. Using NGS Tester, run RETRIEVE/CLEAR CONTINUOUS DTCs.

Step 15:

2. Are there any other DTCs?