Code
B2585
HUMMER
B — Body
Parklamp Control Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Blown fuse or tripped relay in park lamp circuit
- Open, short to ground, or short to battery in wiring harness or connector
- Corroded or loose connector at lamp or chassis ground
- Failed park lamp bulb, LED module, or socket
- Faulty ground or high-resistance ground connection
- Faulty BCM or internal driver transistor
Symptoms
- Park/position lamp(s) inoperative on one or both sides
- Park lamps flicker or operate intermittently
- Park lamps remain ON and do not turn off
- Illumination level abnormally dim or uneven
- Battery drain with vehicle parked (if lamp stays on)
- DTC B2585 stored in BCM and may set a lamp-on warning
What to check
- Retrieve freeze frame and current status with a scan tool; verify active/inactive status and any related codes
- Visually inspect fuses and relays for the park lamp circuit; verify continuity of fuse
- Inspect lamp assemblies, sockets, and connectors for corrosion, melted plastic, or water ingress
- Verify correct bulb/LED type and seating; test/replace bulb with known-good unit
- Inspect wiring harness along routes to bumper/lighting for damage, pinching, or chafing
- Check ground connections for the lamp and BCM; clean and retighten to body ground
Signal parameters
- Expected battery voltage at lamp connector with lights ON: ~12–14.5 V (for supply side)
- Open-circuit/0 V observed if supply is open; near 0 V on output if driver is switched to ground
- Expected current: incandescent park lamp typically 0.5–2.0 A; LED modules typically 0.05–0.5 A (varies by design)
- Ground resistance: chassis ground to battery negative
- BCM driver behavior: switched output or PWM dimming — verify presence/absence of PWM (typical frequency range 50–1000 Hz depending on system)
- Connector pin voltages should switch or pulse when the light switch is operated; stuck voltage indicates short or driver fault
Diagnostic algorithm
- Connect a capable scan tool and read BCM data and stored/active DTCs. Note related codes and lamp status.
- Visually inspect fuses, relays and lamp assemblies; replace any blown fuse and test function. If fuse blows immediately, stop and suspect short to battery.
- With lamp switch ON, backprobe the lamp connector: measure supply voltage and ground reference. If correct voltage is present and lamp does not light, test/replace lamp or module.
- If no voltage at connector, trace supply/backfeed: check fuse circuit and continuity between fuse/relay output and lamp connector. Repair any open circuits.
- If supply present but intermittent or low voltage, inspect connectors and harness for corrosion/damage; repair or replace damaged sections and clean contacts.
- Check ground continuity from lamp socket to battery negative; repair/clean grounds if resistance is high.
- If wiring checks OK, use a lab scope or DVM to check for PWM or switching behavior at BCM output. If BCM output is absent or shorted to battery/ground, disconnect connector and check output pin resistance.
- If output driver appears failed or shorts when connected, isolate BCM by disconnecting load and re-test; if fault persists with no load, suspect BCM/module failure and consider replacement or repair.
- After repair, clear codes and verify proper operation through multiple cycles (on/off, start/stop) and re-scan for reappearance of B2585.
- If intermittent and wiring/lamps test good, consult manufacturer technical service bulletins and wiring diagrams for harness chafe locations or BCM updates.
Likely causes
- Blown fuse or bad connector at lamp (most common)
- Open or shorted harness between BCM and lamp (wire chafe or pinched)
- Corroded lamp/ground connector causing intermittent contact
- Failed lamp/LED module (especially if aftermarket replacements used)
- Faulty BCM output driver or internal module fault (less common)
Fault status
Status
Parklamp Control Circuit Malfunction detected by BCM. Lamp circuit is open/shorting/abnormal; lamp may be inoperative, flickering, stuck on, or causing an electrical fault. Further electrical diagnosis required.
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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