Code
B0688
HUMMER
B — Body
Security System Indicator Circuit High
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the security indicator feed (wiring chafe or pin contacting +12V)
- Failed indicator lamp or LED module with internal fault
- Corroded, loose or damaged connector at indicator or BCM
- Open or high-resistance ground for the indicator circuit
- Faulty BCM or instrument cluster driver output
- Aftermarket alarm/remote start wiring or module incorrectly connected
Symptoms
- Security/anti-theft indicator lamp is ON constantly or behaves abnormally (stays lit, flickers, or does not operate correctly)
- Alarm may not arm/disarm reliably
- Battery drain if circuit is stuck to battery voltage
- Related security messages or inhibit functions in instrument cluster
- Diagnostic trouble code B0688 stored; MIL may not be illuminated (body code)
What to check
- Use a scan tool to read and clear stored codes; record freeze frame and pending codes
- Visually inspect indicator lens, socket/LED module, wiring harness and connectors for damage, corrosion or pin push-out
- Check for aftermarket alarm/remote-start devices and inspect their wiring connections
- Backprobe the indicator connector and BCM connector for voltage and ground with ignition OFF and ON
- Measure continuity and resistance between indicator positive feed and BCM, and between indicator ground and chassis ground
- Wiggle/replicate tests while monitoring the circuit and watch for changes in voltage or codes
Signal parameters
- Expected: Ignition OFF — indicator feed should be low/near 0 V (no constant +12 V)
- Expected: Ignition ON / when system actively flashes — pulsed ~12 V (frequency depends on design, typically 1–2 Hz)
- Fault condition: steady high voltage near battery voltage (>11 V) at indicator feed when it should be low
- Expected resistance: indicator lamp or LED assembly should show a finite resistance when removed and measured to ground (varies by design); open/very high resistance indicates open lamp/LED
Diagnostic algorithm
- Gather info: note vehicle symptoms, history of recent body repairs or aftermarket alarm installs, and record battery voltage.
- Scan: read all body and network codes; note any related U- or B- codes. Clear code and see if B0688 returns immediately or after reproducing the fault.
- Visual inspection: examine indicator assembly, lens, harness, connectors and nearby harness routing for damage, corrosion or pin issues. Repair obvious damage before further testing.
- Backprobe tests: with a digital multimeter, backprobe the indicator positive feed and ground at the indicator connector. With ignition OFF and ON, record voltages. A steady ~12 V when it should be low indicates a short to battery.
- Isolate lamp/LED: disconnect the indicator lamp/LED assembly and measure voltage on the feed. If the high voltage disappears with the lamp disconnected, suspect the lamp/module or connector. If the voltage remains, suspect wiring/BCM.
- Continuity/short check: with battery disconnected, check continuity between the feed circuit and battery positive (to find short). Check continuity from indicator ground to chassis ground (should be low ohms).
- Wiggle and recreate: with connectors connected and meter attached, wiggle harness sections, doors, and wherever flex occurs to reproduce the fault and locate intermittent shorts.
- Connector and pin service: clean corroded pins, repair broken wires, replace damaged connectors or pigtails. Re-test.
- BCM/cluster verification: if wiring and indicator assembly test good and no short is found, verify BCM output using manufacturer diagnostics or swap/replace cluster/BCM only after exhausting wiring and assembly checks.
- Final: clear codes, test drive/operate security system through multiple cycles to confirm repair. Document repair and recheck code status after 24–48 hours of normal use.
Likely causes
- Short to constant 12V at indicator wiring (wiring chafe or pin contact)
- Failed indicator lamp/LED or internal short in the indicator assembly
- Connector corrosion or poor pin contact at BCM/instrument cluster
- Open/poor ground for the indicator circuit
Fault status
Status
Security System Indicator Circuit High — voltage higher than expected detected on the security indicator circuit; stored by the body control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Repair manuals
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138
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