Code
B1970
HUMMER
B — Body
Exterior Lamp Power
Views:
UK: 22
EN: 27
RU: 29
AI status
Completed
Completed
100%
Causes
- Blown fuse or faulty fuse link for exterior lamp circuit
- Faulty exterior lamp relay
- Open or shorted wiring harness or connector to exterior lamps
- Corroded or poor connector/ground at lamp or module
- Failed exterior lamp (burnt bulb or internal short)
- Faulty Body Control Module (BCM) or lighting control module
Symptoms
- One or more exterior lamps do not illuminate (headlights, taillights, marker lights)
- Lights flicker or come and go with vibration or wiggling harness
- Reduced brightness of exterior lamps
- Instrument cluster or message center displays lighting fault or lamp-out message
- Parasitic battery drain when lights should be off
What to check
- Retrieve and record all stored codes and freeze-frame data with a scan tool
- Visually inspect fuses/fuse links and relays related to exterior lamps
- Inspect exterior lamp assemblies, sockets and connectors for corrosion, water intrusion, or damage
- Check for aftermarket lighting or recent body electrical work
- Measure battery voltage and verify charging system operation before tests
- Inspect ground points for cleanliness and tightness
Signal parameters
- Battery voltage at battery terminals: ~12.0–14.5 V (engine running ≈13.5–14.8 V)
- Expected voltage at lamp power feed pin (with lamps on): within 0.5 V of battery voltage
- Ground continuity from lamp ground pin to chassis:
- Typical current draw per halogen headlamp: ~2–7 A (varies by bulb type); LED lamps draw significantly less
- Voltage drop on power feed harness under load:
Diagnostic algorithm
- Connect a professional scan tool, read and record DTCs and freeze-frame data; note which lamps were commanded on when code set.
- Visually inspect fuses and relay for exterior lamp circuits; replace suspicious fuses/relays and retest.
- With ignition on and lamps commanded on, measure voltage at BCM power output and at the lamp connector power pin. Compare to battery voltage. Look for excessive voltage drop.
- Inspect and backprobe lamp connector while operating lights. Wiggle harness and connector to reproduce fault. If fault appears, repair/replace connector or wiring section.
- Check lamp bulbs and sockets for shorted filaments or water intrusion; replace faulty lamp assemblies.
- Check ground integrity at lamp ground and BCM ground points; clean and tighten if high resistance found.
- If wiring and lamps OK, check for aftermarket accessories tied into lighting circuits and disconnect for test.
- If wiring and modules appear intact, perform BCM output bench/diagnostic tests per factory procedure; consider BCM replacement only after confirming module failure.
- Clear codes and perform functional test/road test to confirm repair; re-scan for reappearance of B1970.
Likely causes
- Blown fuse or faulty relay in exterior lamp power feed
- Open or high-resistance connection at lamp connector or ground
- Damaged wiring harness (pinched/chafed) causing intermittent/short condition
- Failed bulb or shorted lamp assembly
- Corroded connectors causing voltage drop
- Less likely: failed BCM or lighting control module
Fault status
Status
Exterior lamp power circuit fault detected — reduced or lost exterior lighting supply. Diagnostic trouble code stored; repair required to restore normal exterior lamp operation.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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Code
B1970
Other
B — Body
Passenger Seatback Forward Switch Circuit Short to Ground
Views:
UK: 28
EN: 52
RU: 36
AI status
Completed
Completed
100%
Causes
- Blown fuse or faulty fuse link for exterior lamp circuit
- Faulty exterior lamp relay
- Open or shorted wiring harness or connector to exterior lamps
- Corroded or poor connector/ground at lamp or module
- Failed exterior lamp (burnt bulb or internal short)
- Faulty Body Control Module (BCM) or lighting control module
Symptoms
- One or more exterior lamps do not illuminate (headlights, taillights, marker lights)
- Lights flicker or come and go with vibration or wiggling harness
- Reduced brightness of exterior lamps
- Instrument cluster or message center displays lighting fault or lamp-out message
- Parasitic battery drain when lights should be off
What to check
- Retrieve and record all stored codes and freeze-frame data with a scan tool
- Visually inspect fuses/fuse links and relays related to exterior lamps
- Inspect exterior lamp assemblies, sockets and connectors for corrosion, water intrusion, or damage
- Check for aftermarket lighting or recent body electrical work
- Measure battery voltage and verify charging system operation before tests
- Inspect ground points for cleanliness and tightness
Signal parameters
- Battery voltage at battery terminals: ~12.0–14.5 V (engine running ≈13.5–14.8 V)
- Expected voltage at lamp power feed pin (with lamps on): within 0.5 V of battery voltage
- Ground continuity from lamp ground pin to chassis:
- Typical current draw per halogen headlamp: ~2–7 A (varies by bulb type); LED lamps draw significantly less
- Voltage drop on power feed harness under load:
Diagnostic algorithm
- Connect a professional scan tool, read and record DTCs and freeze-frame data; note which lamps were commanded on when code set.
- Visually inspect fuses and relay for exterior lamp circuits; replace suspicious fuses/relays and retest.
- With ignition on and lamps commanded on, measure voltage at BCM power output and at the lamp connector power pin. Compare to battery voltage. Look for excessive voltage drop.
- Inspect and backprobe lamp connector while operating lights. Wiggle harness and connector to reproduce fault. If fault appears, repair/replace connector or wiring section.
- Check lamp bulbs and sockets for shorted filaments or water intrusion; replace faulty lamp assemblies.
- Check ground integrity at lamp ground and BCM ground points; clean and tighten if high resistance found.
- If wiring and lamps OK, check for aftermarket accessories tied into lighting circuits and disconnect for test.
- If wiring and modules appear intact, perform BCM output bench/diagnostic tests per factory procedure; consider BCM replacement only after confirming module failure.
- Clear codes and perform functional test/road test to confirm repair; re-scan for reappearance of B1970.
Likely causes
- Blown fuse or faulty relay in exterior lamp power feed
- Open or high-resistance connection at lamp connector or ground
- Damaged wiring harness (pinched/chafed) causing intermittent/short condition
- Failed bulb or shorted lamp assembly
- Corroded connectors causing voltage drop
- Less likely: failed BCM or lighting control module
Fault status
Status
Exterior lamp power circuit fault detected — reduced or lost exterior lighting supply. Diagnostic trouble code stored; repair required to restore normal exterior lamp operation.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Repair manuals
Brands with available manuals
6,642
The library contains 6,642 repair and diagnostic manuals. Choose a brand to open the full manual tree by year, model and trim.
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email