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Home / DTC / B2478 — Reverse Lamp Shorted to Battery

B2478 — Reverse Lamp Shorted to Battery

Detailed page for trouble code B2478.

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Code

B2478

HUMMER B — Body

Reverse Lamp Shorted to Battery

Brand: HUMMER
Type: B — Body
Views: UK: 8 EN: 18 RU: 10
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or chafed wiring contacting a constant +12V source
  • Corroded/damaged reverse lamp socket or bulb base bridging to battery
  • Aftermarket trailer or accessory wiring miswired to battery
  • Faulty reverse light switch (transmission/park/neutral switch) internally shorted to battery feed
  • Shorted connector (pin pushed into another +12V circuit) or water intrusion into connectors
  • Faulty BCM or lamp driver circuit

Symptoms

  • Reverse/back-up lamps illuminated continuously (even with transmission not in reverse)
  • Interior dash reverse indicator shows reverse when not engaged
  • Battery drain with ignition off (if lamps remain powered)
  • Blown fuse on lighting circuit or repeated fuse failure
  • Intermittent operation of reverse lamps or erratic indicator behavior

What to check

  • Confirm symptom: observe lamp state with ignition on/off and transmission in/out of reverse
  • Scan for related DTCs and BCM freeze-frame data (voltage/current at time of fault)
  • Visually inspect bulbs, sockets, wiring harness, connectors and trailer plug for damage or corrosion
  • Remove reverse lamp bulb(s) and inspect socket for signs of short or corrosion
  • Check fuse(s) and any related relays for the reverse/tail lighting circuit
  • Measure voltage at reverse lamp connector with harness connected and with bulb removed (key on, engine off, and with transmission in/out of reverse)

Signal parameters

  • Expected reverse lamp circuit voltage: Off ≈ 0 V (or open); On (reverse engaged) ≈ battery voltage (12–14 V)
  • Measured voltage with ignition off (or reverse off) should be ≈0 V; a steady ~12 V indicates short to battery
  • Typical incandescent reverse lamp current: ~0.5–3 A per lamp (depends on lamp type); LED lamps draw substantially less
  • Continuity to battery positive when circuit is off indicates an unwanted connection/short to battery

Diagnostic algorithm

  1. Reproduce symptom and record lamp behavior (key on/off, transmission positions).
  2. Scan BCM and note freeze-frame/related codes. Disconnect power if testing to prevent battery drain.
  3. Visually inspect rear harness, bulb sockets, lamp assemblies, ground points and trailer connector for damage, corrosion or foreign metal.
  4. Remove the reverse bulb(s). With bulb removed, check voltage at the harness connector: If ~12 V with reverse off, a short to battery exists upstream of the bulb.
  5. Disconnect trailer connector and rear lamp connectors. If voltage returns to normal, isolate and repair trailer/add-on wiring.
  6. With connectors disconnected, measure resistance from the reverse lamp feed to battery positive and to ground to locate unintended connections. Wiggle test harness near hinges and body seams while monitoring voltage.
  7. If the short appears to originate at a connector, repair/replace the connector and clean contacts. If harness damage is found, repair or replace the damaged section and protect with conduit.
  8. If harness and external wiring check good, backprobe and test the BCM/lamp-driver output. If the module output is shorted to battery and wiring is confirmed good, consult manufacturer procedure for BCM replacement or repair.
  9. After repair, clear codes, confirm correct operation through several cycles (ignition on/off, transmission in/out of reverse), and verify no battery drain.
  10. Advise customer of any aftermarket wiring found and proper repair/replacement steps.

Likely causes

  • Chafed harness at trunk/tailgate hinge contacting constant hot feed
  • Corroded bulb socket allowing battery-positive contact path
  • Trailer wiring connector miswired or shorted to battery feed
  • Damaged ground or positive splice near rear lighting harness
  • Connector pins pushed together or foreign metal debris in connector

Fault status

⚠️ Status
Stored when the body control module detects battery voltage or an unexpected high-voltage/current condition on the reverse lamp circuit while the circuit should be off or when the measured parameters exceed predefined thresholds. The code indicates a possible short to battery or improper feed on the reverse lamp circuit and requires circuit isolation and inspection.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-1.5 hours

Similar codes

B2479 B2540 B2550 B2578 U0140
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Code

B2478

Other B — Body

ANTI THEFT INPUT SIGNAL SHORT TO GROUND

Brand: Other
Type: B — Body
Views: UK: 16 EN: 30 RU: 19
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or chafed wiring contacting a constant +12V source
  • Corroded/damaged reverse lamp socket or bulb base bridging to battery
  • Aftermarket trailer or accessory wiring miswired to battery
  • Faulty reverse light switch (transmission/park/neutral switch) internally shorted to battery feed
  • Shorted connector (pin pushed into another +12V circuit) or water intrusion into connectors
  • Faulty BCM or lamp driver circuit

Symptoms

  • Reverse/back-up lamps illuminated continuously (even with transmission not in reverse)
  • Interior dash reverse indicator shows reverse when not engaged
  • Battery drain with ignition off (if lamps remain powered)
  • Blown fuse on lighting circuit or repeated fuse failure
  • Intermittent operation of reverse lamps or erratic indicator behavior

What to check

  • Confirm symptom: observe lamp state with ignition on/off and transmission in/out of reverse
  • Scan for related DTCs and BCM freeze-frame data (voltage/current at time of fault)
  • Visually inspect bulbs, sockets, wiring harness, connectors and trailer plug for damage or corrosion
  • Remove reverse lamp bulb(s) and inspect socket for signs of short or corrosion
  • Check fuse(s) and any related relays for the reverse/tail lighting circuit
  • Measure voltage at reverse lamp connector with harness connected and with bulb removed (key on, engine off, and with transmission in/out of reverse)

Signal parameters

  • Expected reverse lamp circuit voltage: Off ≈ 0 V (or open); On (reverse engaged) ≈ battery voltage (12–14 V)
  • Measured voltage with ignition off (or reverse off) should be ≈0 V; a steady ~12 V indicates short to battery
  • Typical incandescent reverse lamp current: ~0.5–3 A per lamp (depends on lamp type); LED lamps draw substantially less
  • Continuity to battery positive when circuit is off indicates an unwanted connection/short to battery

Diagnostic algorithm

  1. Reproduce symptom and record lamp behavior (key on/off, transmission positions).
  2. Scan BCM and note freeze-frame/related codes. Disconnect power if testing to prevent battery drain.
  3. Visually inspect rear harness, bulb sockets, lamp assemblies, ground points and trailer connector for damage, corrosion or foreign metal.
  4. Remove the reverse bulb(s). With bulb removed, check voltage at the harness connector: If ~12 V with reverse off, a short to battery exists upstream of the bulb.
  5. Disconnect trailer connector and rear lamp connectors. If voltage returns to normal, isolate and repair trailer/add-on wiring.
  6. With connectors disconnected, measure resistance from the reverse lamp feed to battery positive and to ground to locate unintended connections. Wiggle test harness near hinges and body seams while monitoring voltage.
  7. If the short appears to originate at a connector, repair/replace the connector and clean contacts. If harness damage is found, repair or replace the damaged section and protect with conduit.
  8. If harness and external wiring check good, backprobe and test the BCM/lamp-driver output. If the module output is shorted to battery and wiring is confirmed good, consult manufacturer procedure for BCM replacement or repair.
  9. After repair, clear codes, confirm correct operation through several cycles (ignition on/off, transmission in/out of reverse), and verify no battery drain.
  10. Advise customer of any aftermarket wiring found and proper repair/replacement steps.

Likely causes

  • Chafed harness at trunk/tailgate hinge contacting constant hot feed
  • Corroded bulb socket allowing battery-positive contact path
  • Trailer wiring connector miswired or shorted to battery feed
  • Damaged ground or positive splice near rear lighting harness
  • Connector pins pushed together or foreign metal debris in connector

Fault status

⚠️ Status
Stored when the body control module detects battery voltage or an unexpected high-voltage/current condition on the reverse lamp circuit while the circuit should be off or when the measured parameters exceed predefined thresholds. The code indicates a possible short to battery or improper feed on the reverse lamp circuit and requires circuit isolation and inspection.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-1.5 hours

Similar codes

B2479 B2540 B2550 B2578 U0140
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