B0104 – SRS Control Module Internal Fault

System: Body | Standard: ISO/SAE Controlled | Fault type: General

Definition source: SAE J2012/J2012DA (industry standard)

DTC B0104 indicates the Supplemental Restraint System (SRS) control module has detected an internal fault within itself. Because SRS architectures, self-test routines, and fault decision logic vary by vehicle, the exact conditions that trigger B0104 and the data available to confirm it can differ across platforms. Treat this code as a module-reported integrity or self-diagnostic failure rather than proof that a specific airbag, sensor, or wiring branch is bad. Use the vehicle’s service information to identify the precise monitor name, enabling conditions, stored freeze-frame or event records, and any required post-repair initialization steps before clearing codes or returning the vehicle to service.

What Does B0104 Mean?

B0104 means the SRS control module has identified an internal fault condition. Based strictly on the official definition, the issue is within the control module’s internal operation (for example, internal self-checks, internal memory, internal processing, or internal monitoring functions), not a specific external circuit. SAE J2012 defines how DTCs are structured and labeled, but the internal criteria the module uses to set this code can vary by vehicle. Because the SRS control module is responsible for monitoring restraint components and commanding deployment when required, any internal-fault DTC should be treated as safety-significant until verified and corrected using service information and proper SRS-safe diagnostic procedures.

Quick Reference

• Subsystem: Supplemental Restraint System (SRS) control module (airbag control unit) internal diagnostics
• Common triggers: Failing internal self-test, internal memory/processing error, corrupted configuration, unstable module power/ground affecting internal checks, or repeated resets during operation
• Likely root-cause buckets: Power/ground integrity, connector/pin fit at the module, network communication conditions affecting module operation (varies by vehicle), module software/configuration, or SRS control module hardware fault
• Severity: High safety impact; SRS may be disabled or may not perform as designed, typically accompanied by an airbag warning indicator
• First checks: Verify battery health and charging stability, check SRS module power/ground and voltage-drop under load, inspect connectors for corrosion/loose terminals, confirm no recent low-voltage events, and check for related codes
• Common mistakes: Replacing airbags/sensors first, clearing codes repeatedly without fixing power/ground, probing SRS connectors improperly, or condemning the module without confirming feeds/grounds and required configuration steps

Theory of Operation

The SRS control module monitors restraint system inputs and continuously runs internal diagnostics to confirm the module can reliably evaluate crash signals and command restraint outputs when needed. In addition to watching external circuits (such as sensors and squib circuits), the module performs internal checks on items like processor operation, memory integrity, watchdog timing, and stored configuration data. These checks occur at key-on and often continue while driving, with results stored as fault records when something falls outside expected behavior.

B0104 is set when the module’s internal diagnostics indicate a fault inside the SRS control module itself. Depending on vehicle design, external issues such as unstable power/ground, repeated resets, or poor connector contact can cause internal checks to fail and appear as an internal fault. For accurate diagnosis, confirm the module’s electrical integrity and operating environment before concluding the module has an internal hardware or software problem.

Symptoms

• Airbag warning: SRS/airbag indicator illuminated or message displayed
• Stored DTC: B0104 present as current or history in the SRS control module
• SRS disabled: Restraint functions may be inhibited or limited until the fault is cleared and the system passes self-check
• Intermittent reset: Warning light may flicker or return after clearing if power/ground is unstable (varies by vehicle)
• Multiple related codes: Additional restraint or communication codes may accompany B0104 depending on how the module reports internal failures
• No drivability change: Engine performance often unaffected, but safety functionality may be compromised

Common Causes

• Low system voltage during start-up or a weak battery causing the SRS module’s internal self-test to fail
• Poor power feed or ground to the SRS control module (loose fasteners, corrosion, high resistance in a splice)
• Connector issues at the SRS control module (backed-out terminals, poor pin fit, contamination, damage)
• Harness damage in the SRS module power/ground/CAN communication paths (chafing, pinched wiring, prior repair issues)
• Intermittent communication faults on the network the SRS control module uses to exchange status with other modules
• Internal SRS control module fault detected by self-diagnostics (memory/processor/watchdog or internal reference checks)
• Software/firmware corruption or a module configuration mismatch after programming, replacement, or a low-voltage event
• Aftermarket electrical accessories or improper jump-start/charging procedures contributing to electrical noise or low-voltage conditions

Diagnosis Steps

Tools that help include a scan tool that can access SRS data, read freeze-frame/event data, and monitor module voltage/status PIDs; a digital multimeter; test leads suitable for non-invasive backprobing; and basic hand tools for connector inspection. A battery tester/charger and a method to review wiring diagrams/service information are strongly recommended. Use approved SRS safety procedures for your platform.

1. Confirm the code and context. Scan all modules and record B0104 plus any accompanying power, network, or ignition-related DTCs. Save freeze-frame/event records and note whether the code is current or history, and whether it resets immediately or only after a key cycle.
2. Check SRS indicators and scan tool status. Verify the warning lamp behavior and review SRS control module status PIDs (module internal fault flag, supply voltage reading if available, and communication status). If the scan tool cannot communicate with the SRS module, treat that as a priority symptom and proceed to power/ground/network checks.
3. Stabilize and evaluate the power supply. Test the battery and charging system condition. Charge the battery if needed and clear low-voltage conditions before deeper diagnosis. Recheck whether B0104 returns after voltage is stabilized and the vehicle is started normally.
4. Perform a visual inspection (no disassembly beyond what service info allows). Inspect accessible SRS-related fuses, module mounting area, and harness routing. Look for signs of water intrusion, damaged insulation, recent repair work, or harness tension that could stress the module connector.
5. Inspect SRS module connectors and terminal condition. Following the required SRS disable procedure for the vehicle, disconnect the SRS control module connectors as directed by service information. Check for bent pins, spread terminals, corrosion, contamination, or backed-out terminals. Confirm connectors latch fully and any secondary locks are engaged.
6. Verify module power and ground with key states. Using wiring diagrams, identify all SRS module power feeds and grounds. Check for proper power presence in the required key positions and verify ground integrity. Use voltage-drop testing under load on both the power feed(s) and ground path(s) to find high resistance that a simple continuity check can miss.
7. Check for intermittent faults with a wiggle test. With the system safely enabled as applicable and the scan tool monitoring SRS supply voltage/status and communication, gently wiggle the harness near the module, fuse/relay areas, and known flex points. Watch for PID dropouts, lamp flicker, or the DTC resetting, which indicates a connection or wiring issue.
8. Evaluate network integrity if applicable. If other modules logged communication codes or the SRS module shows intermittent communication, inspect the network wiring to the SRS module for damage and connector issues. Verify the network is not shorted to power/ground and is not open, using service information procedures for the platform.
9. Rule out configuration/software issues. If B0104 appeared after battery replacement, low-voltage events, module replacement, or programming, verify correct module configuration/coding per service information. If supported, perform the appropriate module reset/relearn routines and recheck for DTC return.
10. Make a repair decision based on evidence. If power/ground integrity, connectors, and network checks are all verified good and B0104 returns as a current code (especially immediately after clearing), the remaining evidence points toward an internal SRS control module fault. Follow service information for confirmation steps and any required programming procedures if replacement is indicated.

Professional tip: When dealing with “internal fault” SRS codes, prioritize proving the module’s power and ground quality under real load. Many repeat comebacks happen because voltage-drop testing was skipped and a marginal ground or feed caused the module to fail self-checks intermittently, mimicking an internal defect.

Possible Fixes & Repair Costs

Repair costs for B0104 can vary widely because the underlying issue may be a simple power/ground or connector problem, or it may require module programming or replacement. Final cost depends on confirmed diagnosis, parts availability, and labor time based on vehicle design.

• Restore power/ground integrity: Clean, tighten, or repair the SRS control module power feeds, grounds, and related terminals after confirming excessive voltage drop or poor continuity.
• Connector and terminal service: Reseat connectors, correct pin fit issues, remove corrosion, and repair damaged locks or terminal tension problems that can cause module resets or internal self-test failures.
• Harness repair: Repair chafed, pinched, stretched, or previously spliced wiring affecting the SRS module’s power, ground, or communication paths, then verify stability with a wiggle test.
• Correct low system voltage causes: Diagnose and fix charging/starting voltage instability (varies by vehicle) that can trigger module internal-fault monitoring, then retest for code return.
• Reprogram/initialize per service information: If supported, perform required configuration, setup, or software update procedures for the SRS control module using approved service methods.
• Replace the SRS control module: Replace only after confirming external circuits are stable and the fault persists; follow required setup, coding, and post-repair verification steps.

Can I Still Drive With B0104?

B0104 indicates an internal fault detected by the SRS control module, which can disable or degrade airbag and seat-belt pretensioner operation. Driving may still be possible, but it is not recommended to rely on full supplemental restraint protection until the fault is repaired and the warning indicator is off. If other warnings appear (such as reduced power, charging problems, or multiple control modules losing communication), or if the vehicle shows starting/voltage instability, avoid driving and arrange service.

What Happens If You Ignore B0104?

Ignoring B0104 can leave the vehicle with an impaired SRS system, meaning airbags and pretensioners may not deploy as intended during a crash, or the system may remain disabled as a protective response. The warning light will typically stay on, and an unresolved underlying power/ground or network issue can lead to additional faults, intermittent resets, or repeated code returns after clearing.

Last updated: March 13, 2026

Vehicles Commonly Affected by B0104

• Vehicles with integrated SRS control modules: Platforms where the airbag controller performs frequent internal self-checks and stores internal-fault codes.
• Vehicles with multiple restraint components: Systems with front/side/curtain airbags and pretensioners that increase module monitoring complexity.
• Vehicles with high cabin moisture exposure: Designs where connector corrosion risk is higher (location varies by vehicle).
• Vehicles with under-seat or floor-area wiring: Harness routing that is more susceptible to movement, pinching, or contamination (varies by vehicle).
• Vehicles with recent electrical work: Battery replacement, interior repairs, or wiring modifications that may disturb power/ground or connectors.
• Vehicles with intermittent low voltage history: Charging or battery issues that can cause controller resets and self-test failures.
• Vehicles with prior collision repairs: Repairs that may affect module mounting, connectors, or harness routing (varies by vehicle).

For any repair affecting the SRS system, follow the correct safety steps and verification procedure so the restraint warning indicator turns off and the code does not return.