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Pinpoint Test I: DTC B1921




Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)


Pinpoint Tests


Pinpoint Test I: DTC B1921

Refer to Wiring Diagram Set 46, Supplemental Restraint System for schematic and connector information. Diagrams By Number

Lamp Fault Codes (LFCs)

The following Lamp Fault Code (LFC) indicates the specific fault associated with DTC B1921:

- LFC 1-4 - Air Bag Diagnostic Monitor Ground Circuit Open

Normal Operation

The Restraints Control Module (RCM) monitors the resistance between the case ground and the reference ground at C310a pin 16, circuit 676 (PK/OG).

If the RCM detects a difference in resistance, it will store DTC B1921 in memory and flash LFC 1-4 on the air bag warning indicator.

- DTC B1921 Air Bag Diagnostic Monitor Ground Circuit Open - If the RCM detects a difference in resistance between the ground circuit and the RCM mounting ground, it will set this DTC.

This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- RCM not securely mounted
- RCM



PINPOINT TEST I: DTC B1921

WARNING: Remove restraint system diagnostic tools from the vehicle prior to road testing. If tools are not removed, the supplemental restraint system (SRS) device may not deploy in a crash. Failure to follow this instruction may result in serious personal injury or death in a crash and possibly violate vehicle safety standards.

WARNING: Never probe the electrical connectors on air bag, Safety Canopy(R) or side air curtain modules. Failure to follow this instruction may result in the accidental deployment of these modules, which increases the risk of serious personal injury or death.

WARNING: Always tighten the fasteners of the restraints control module (RCM) and impact sensor (if equipped) to the specified torque. Failure to do so may result in incorrect restraint system operation, which increases the risk of personal injury or death in a crash.

NOTICE: Use the correct probe adapter(s) from the Flex Probe Kit when taking measurements. Failure to use the correct probe adapter(s) may damage the connector. Most faults are due to connector and/or wiring concerns. Carry out a thorough inspection and verification before proceeding with the pinpoint test. Inspection and Verification

NOTE: The Supplemental Restraint System (SRS) must be fully operational and free of faults before releasing the vehicle to the customer.

NOTE: SRS components should only be disconnected or reconnected when instructed to do so within a pinpoint test step. Failure to follow this instruction may result in incorrect diagnosis of the SRS.

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I1 CHECK FOR ON-DEMAND AND CONTINUOUS DTCs


- Enter the following diagnostic mode on the scan tool: Self-Test - RCM.
- Was DTC B1921 retrieved on-demand during self-test?

Yes
The fault condition is still present. This fault cannot be cleared until it is corrected and the DTC is no longer retrieved during the on-demand self-test. GO to I2.

No
This is an intermittent fault when present as a continuous memory DTC only (DTC not retrieved on demand). The fault condition is not present at this time. GO to I6.

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I2 INSPECT THE RCM MOUNTING AND MOUNTING SURFACE


- Ignition OFF.
- Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering and Repowering Supplemental Restraint System (SRS) Depowering and Repowering.
- Inspect the RCM mounting bolts and make sure they are fully seated and tightened correctly.
- Remove the RCM. Refer to Restraints Control Module (RCM) Service and Repair.
- Visually inspect the RCM and mounting surface for damage, corrosion or dirt.
- Was a significant amount of corrosion or dirt found, or was the RCM attached to the mounting surface incorrectly or were the RCM retainers not fully seated and tightened correctly?

Yes
CLEAN and TIGHTEN the retainers. REPAIR the mounting surface as necessary. REINSTALL the RCM and mounting bracket to the mounting surface. GO to I7.

No
GO to I3.

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I3 INSTALL THE RCM AND CARRY OUT THE SELF-TEST


- Clean the RCM mounting surface.
- Install the RCM. Refer to Restraints Control Module (RCM) Service and Repair.
- Repower the SRS. Do not prove out the SRS at this time. Refer to Supplemental Restraint System (SRS) Depowering and Repowering Supplemental Restraint System (SRS) Depowering and Repowering.
- Enter the following diagnostic mode on the scan tool: Self-Test - RCM.
- Was DTC B1921 retrieved on-demand during self-test?

Yes
GO to I4.

No
CHECK for causes of intermittent high resistance on circuit 676 (PK/OG) or the chassis ground. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently. ACTIVATE other systems in the same wire harness. REPAIR any intermittent concerns found. GO to I7.

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I4 CHECK GROUND CIRCUIT 676 (PK/OG) FOR HIGH RESISTANCE


- Ignition OFF.
- Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering and Repowering Supplemental Restraint System (SRS) Depowering and Repowering.
- Disconnect: RCM C310a and C310b.
- Measure the resistance between RCM C310a-16, circuit 676 (PK/OG), harness side and the RCM case ground.
- Is the resistance less than 5 ohms?

Yes
GO to I5.

No
REPAIR circuit 676 (PK/OG). GO to I7.

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I5 CONFIRM THE RCM FAULT


NOTE: Make sure all Restraint System Diagnostic Service Tools, sensor electrical connectors and the RCM electrical connectors are connected before carrying out the self-test. If not, erroneous DTCs will be recorded.

- Connect: RCM C310a and C310b.
- Repower the SRS. Do not prove out the SRS at this time. Refer to Supplemental Restraint System (SRS) Depowering and Repowering Supplemental Restraint System (SRS) Depowering and Repowering.
- Enter the following diagnostic mode on the scan tool: Self-Test - RCM.
- Was DTC B1921 retrieved on-demand during self-test?

Yes
INSTALL a new RCM. REFER to Restraints Control Module (RCM) Service and Repair. GO to I7.

No
In the process of diagnosing the fault, the fault condition has become intermittent. CHECK for causes of the intermittent fault in the areas previously worked in, particularly the pins and terminals of electrical connectors that were disconnected. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently. Do not install any new SRS components at this time. SRS components should only be installed when directed to do so in the pinpoint test. REPAIR any intermittent wiring, terminal or connector concerns found. GO to I7.

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I6 CHECK FOR AN INTERMITTENT FAULT


- Ignition OFF.
- Enter the following diagnostic mode on the scan tool: Self-Test - RCM.
- Was DTC B1921 retrieved on-demand during self-test?

Yes
The fault condition is now present. This fault cannot be cleared until it is corrected and the DTC is no longer retrieved during the on-demand self-test. GO to I2.

No

CHECK for causes of intermittent high resistance on circuit 676 (PK/OG) or the chassis ground. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently. ACTIVATE other systems in the same wire harness. Do not install any new SRS components at this time. SRS components should only be installed when directed to do so in the pinpoint test. REPAIR any intermittent wiring, terminal or connector concerns found. GO to I7.

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I7 CHECK FOR ADDITIONAL SRS DTCs


- Ignition OFF.
- WARNING: Turn the ignition OFF and wait one minute to deplete the backup power supply. Failure to follow this instruction may result in serious personal injury or death in the event of an accidental deployment.
- Reconnect all SRS components (if previously disconnected).
- If previously directed to depower the SRS, repower the SRS. Do notprove out the SRS at this time. Refer to Supplemental Restraint System (SRS) Depowering and Repowering Supplemental Restraint System (SRS) Depowering and Repowering.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self-Test - RCM.
- Are any RCM DTCs retrieved on-demand during self-test?

Yes
Do not clear any DTCs until all DTCs have been resolved. GO to the DTC Charts for pinpoint test direction. [1][2]Diagnostic Trouble Code Descriptions

No
CLEAR all RCM continuous memory DTCs. PROVE OUT the SRS. Repair is complete. RETURN the vehicle to the customer.

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