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Home >> Mercury >> 2009 >> Grand Marquis V8-4.6L >> Repair and Diagnosis >> Restraints and Safety Systems >> Air Bag Systems >> Testing and Inspection >> Pinpoint Tests >> Pinpoint Test H: DTC B1921

Pinpoint Test H: DTC B1921




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

Pinpoint Test H: 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

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.

NOTE: A resistance difference as low as 10 ohms may set the LFC.

Normal Operation

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

If the RCM detects a difference in resistance, it will store DTC B1921 in memory, 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:
- RCM bracket not securely mounted
- Wiring, terminals or connectors
- RCM



PINPOINT TEST H: 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.

NOTICE: Use the correct probe adapter(s) when taking measurements. Failure to use the correct probe adapter(s) may damage the connector.

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.

NOTE: 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

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H1 RETRIEVE SRS 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 on-demand during self test. GO to H2.

No
This is an intermittent fault when present as a CMDTC only. GO to H6.

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H2 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.
- 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 H7.

No
GO to H3.

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H3 INSTALL THE RCM AND CARRY OUT THE ON-DEMAND 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.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - RCM.
- Was DTC B1921 retrieved on-demand during self-test?

Yes
GO to H4.

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 wiring, terminal or connector concerns found. GO to H7.

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H4 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 H5.

No
REPAIR circuit 676 (PK/OG). GO to H7.

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H5 CONFIRM THE RCM FAULT


NOTE: Make sure all restraint system diagnostic tools, sensor electrical connectors and the RCM electrical connectors are connected before carrying out the self test. If not, 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 B1892 retrieved on-demand during self-test?

Yes
INSTALL a new RCM. REFER to Restraints Control Module (RCM) Service and Repair. GO to H7.

No
CHECK for causes of the intermittent fault. 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 H7.

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H6 CHECK FOR AN INTERMITTENT FAULT


- 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 on-demand during self test. GO to H2.

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 H7.

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H7 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 DTCs retrieved on-demand during self-test?

Yes
Do not clear any DTCs until all DTCs have been resolved. GO to the Supplemental Restraint System (SRS) DTC Chart for pinpoint test direction. Diagnostic Trouble Code Tests and Associated Procedures

No
CLEAR all CMDTCs. PROVE OUT the SRS. REPAIR is complete. RETURN the vehicle to the customer.

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