Code
B1799
Other
B — Body
Lamp Turn Signal Front Output Circuit Open
AI status
Completed
Completed
100%
Causes
- Open or broken wiring between body control module (BCM) and front lamp
- Corroded or damaged lamp socket or connector
- Burned-out bulb or failed LED module
- Blown fuse or fusible link in lighting circuit
- Faulty ground connection for the lamp circuit
- Defective BCM/lighting driver or relay
Symptoms
- Front turn signal on the affected side does not illuminate
- Turn signal indicator on dash may not flash or may show error
- No voltage present at the front lamp socket when turn signal is activated
- Possible other lighting faults if common fuse or ground is shared
- Related stored DTC(s) in BCM
What to check
- Scan BCM for stored lamp-related codes and freeze-frame data
- Visually inspect front lamp assembly, socket, connector and wiring for damage/corrosion
- Check relevant fuses and fusible links for continuity
- Back-probe lamp connector with turn signal on to measure voltage
- Measure continuity/resistance between BCM output pin and lamp socket pin
- Check ground continuity from lamp socket ground to chassis/negative battery
Signal parameters
- Nominal battery/supply voltage with engine off or key on: 11–14.5 V
- Open-circuit condition: infinite/OL continuity; no measurable voltage when output commanded
- Typical incandescent filament DC resistance (cold): ~2–15 Ω (varies by bulb rating)
- LED modules: low current with internal driver — effective resistance not comparable to filament bulbs
- Turn signal flash rate: approximately 0.5–2.0 Hz (60–120 cycles per minute) when functioning
Diagnostic algorithm
- Retrieve all related DTCs and BCM data with a scan tool; note which front lamp (left/right) is reported.
- Inspect the lamp, socket and connector visually; remove lamp and check filament or LED for obvious failure.
- Check fuses/fusible links for the lighting circuits and replace if blown. Re-scan for code persistence.
- With key ON and turn signal activated, back-probe the lamp power terminal at the socket and measure voltage. Record results.
- If no voltage at socket, check continuity between the socket power pin and the BCM output pin. If open, trace harness for damage or disconnects.
- Check ground: measure continuity from lamp ground to battery negative; repair any high-resistance or open ground.
- If wiring and grounds are good but no output voltage, command the output from the scan tool (if supported) and observe BCM output. If BCM does not drive, suspect module/driver failure.
- If intermittent, perform wiggle tests along harness and tap connectors to reproduce fault while measuring voltage or operation.
- Repair or replace damaged wiring, connectors, sockets, bulbs or BCM as indicated. Use OEM-quality parts for connectors and sealed sockets where applicable.
- Clear codes, operate turn signals and re-scan to confirm repair. Road-test to verify proper function.
Likely causes
- Broken/shorted harness or pinched wiring to front lamp
- Corroded lamp socket contacts preventing continuity
- Bulb filament open or LED driver failed
- Open ground or high-resistance ground return
- Blown fuse protecting the front lamp circuit
- BCM output transistor/driver failure
Fault status
Status
Front turn signal lamp output circuit open — no continuity or no voltage detected at front lamp output.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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