Pinpoint Test H: LFC 14/DTC B1921
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Pinpoint Tests
Pinpoint Test H: LFC 14/DTC B1921
Refer to Wiring Diagram Set 46, Supplemental Restraint System for schematic and connector information. Diagrams By Number
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 this DTC.
Normal Operation
The Restraints Control Module (RCM) continuously monitors the resistance between the ground connections at the mounting bolts and the reference ground at C2041a pin 16, circuit 1203 (BK/LB). If the RCM detects a difference in resistance, it will store DTC B1921 in memory and flash Lamp Fault Code (LFC) 14 on the air bag warning indicator.
- DTC B1921 Air Bag Diagnostic Monitor Ground Circuit Open - If the RCM detects a resistance difference between the case ground and pin 16 of C2041a, it will set this DTC.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- RCM mounting
- RCM
PINPOINT TEST H: LFC 14/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) from the Flex Probe Kit when making 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: Supplemental Restraint System (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: The SRS must be fully operational and free of faults before releasing the vehicle to the customer.
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H1 RETRIEVE RCM DTCs
- Enter the following diagnostic mode on the scan tool: Self Test - RCM.
- Was RCM DTC B1921 retrieved on-demand during the self test?
Yes
This fault cannot be cleared until it is corrected and the DTC is no longer retrieved during the on-demand self test. GO to H2.
No
This is an intermittent fault when present as a CMDTC only. The fault condition is not present at this time. GO to H5.
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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 and make sure that the retaining bolts 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, the RCM attached to the mounting surface incorrectly or were the RCM bolts not fully seated and tightened correctly?
Yes
CLEAN, TIGHTEN bolts or REPAIR the mounting surface as necessary. REINSTALL the RCM to the mounting surface. GO to H6.
No
GO to H3.
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H3 INSTALL THE RCM AND CARRY OUT THE ON-DEMAND SELF TEST
- Clean the RCM mounting surfaces and bolts.
- 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 RCM DTC B1921 retrieved on-demand during the self test?
Yes
GO to H4.
No
Fault corrected. GO to H6.
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H4 CHECK GROUND CIRCUIT 1203 (BK/LB) 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 C2041a and C2041b.
- Measure the resistance between RCM C2041a-16, circuit 1203 (BK/LB), harness side and the RCM case ground.
- Is resistance less than 5 ohms?
Yes
INSTALL a new RCM. REFER to Restraints Control Module (RCM) Service and Repair. GO to H6.
No
REPAIR circuit 1203 (BK/LB). GO to H6.
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H5 CHECK FOR AN INTERMITTENT FAULT
- Enter the following diagnostic mode on the scan tool: Self Test - RCM.
- Was RCM DTC B1921 retrieved on-demand during the self test?
Yes
GO to H2.
No
CHECK for causes of intermittent high resistance on circuit 1203 (BK/LB) or the chassis ground. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition 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 H6.
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H6 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 the self test?
Yes
Do not clear any DTCs until all DTCs have been resolved. GO to the DTC Chart for pinpoint test direction. Diagnostic Trouble Code Tests and Associated Procedures
No
CLEAR all RCM CMDTCs. PROVE OUT the SRS. Repair is complete. RETURN the vehicle to the customer.
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