Code
B2588
HUMMER
B — Body
Park Lamp Relay Output Circuit High (BCM)
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the park lamp relay control/wiring
- Failing or stuck park lamp relay contacting battery voltage
- Corroded, damaged, or loose connector at BCM or relay
- Aftermarket lighting or wiring tied into the park lamp circuit
- Internal BCM driver failure
- Blown or incorrect fuse allowing unintended feed to the circuit
Symptoms
- Park lamps may remain ON when they should be OFF or behave erratically
- Battery drain with park lamps unexpectedly energized
- One or more exterior parking/tail lamps inoperative or flickering
- Illumination warning or stored BCM fault message
- Related fuse may blow intermittently
What to check
- Retrieve freeze frame and confirm B2588 is current or historic using a scan tool
- Visual inspection of park lamp relay, fuse, BCM connector and wiring for damage, corrosion, or aftermarket splices
- Check for proper relay operation by swapping with a known-good identical relay if possible
- Measure voltage at the BCM park-lamp output terminal with ignition ON and with relay energized/de-energized
- Disconnect the park lamp relay coil or lamp harness to see if the code clears (isolates load vs. driver)
- Perform continuity and resistance checks between BCM pin and relay/lamps to detect short to battery or short to ground
Signal parameters
- Expected: control output toggles between near 0 V (off) and battery voltage (~12 V) when commanding relay; specifics vary by vehicle
- With relay coil disconnected and output commanded OFF: voltage should be low (near 0 V); a high voltage indicates a short to battery
- With relay coil disconnected and output commanded ON: voltage should be battery voltage (approx. system voltage)
- Resistance from BCM output to battery positive should be open when relay not energized; low resistance indicates direct short
- No excessive current draw from BCM driver when relay coil disconnected; elevated current suggests internal driver fault or low impedance path
Diagnostic algorithm
- Verify DTC: Connect a capable scan tool and confirm B2588 is present; note freeze frame and related codes. Clear codes and attempt to re-create.
- Visual: Inspect park lamp relay, fuse, BCM connector, harness routing and lamp sockets for corrosion, pin damage, melted insulation or aftermarket splices.
- Relay isolation: With ignition OFF, remove the park lamp relay and inspect contacts. Swap with a known-good identical relay. Re-scan for code.
- Load disconnect test: Disconnect the park lamp harness or relay coil connector, then cycle ignition and monitor for B2588. If code clears, problem is in load/lamp harness or lamp sockets.
- Voltage test at BCM: Back-probe the BCM output terminal. With output commanded OFF, verify voltage is low (near 0 V). With output commanded ON, verify approximate battery voltage. Record readings.
- Short/continuity test: With battery disconnected, measure resistance between the BCM output and battery positive and between the output and ground to locate short. Repair any short to battery or high-resistance connections.
- Inspect downstream components: Check bulbs, sockets, connectors and any aftermarket devices tied to the park lamp circuit. Repair or remove as needed.
- If wiring and load are good: suspect BCM driver. Confirm with manufacturer diagnostic flow — bench tests or substitution of known-good BCM if available. Do not replace BCM before ruling out wiring/relay/load issues.
- Reassemble, clear codes, and perform road/operation test ensuring lamp operation is normal and code does not return.
Likely causes
- Short to battery on the relay control wire (most likely)
- Faulty or welded relay contacts allowing feed back to BCM
- Corroded connector or pin causing poor isolation
- Aftermarket accessory wiring tied into circuit
- BCM output transistor has failed (least likely, verify wiring first)
Fault status
Status
BCM has detected a HIGH voltage condition on the Park Lamp Relay Output Circuit (park lamp control).
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
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