B2490

Code

Other B — Body

UNDERHOOD LAMP OUTPUT CIRCUIT Short to Battery

Brand: Other

Type: B — Body

Views: UK: 33 EN: 33 RU: 37

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Damaged or chafed wiring contacting a constant battery feed
Faulty or shorted underhood lamp (bulb/LED) or lamp assembly
Corroded/loose connector or pin causing power feed to bleed into the output
Failed body/control module output driver (internal transistor)
Aftermarket accessory tied into the lighting circuit incorrectly
Blown or incorrect fuse or fusible link allowing backfeed

Symptoms

Underhood lamp stays ON continuously or comes on unexpectedly
Battery draining when vehicle is off (parasitic draw)
Blown fuse or repeated fuse failures on lighting circuit
Related body module warnings or stored body DTCs
Lamp does not respond to hood switch or lighting control

What to check

Scan for stored body/module DTCs and freeze-frame data; confirm B2490 is current or historic
Visual inspection of underhood lamp, connector and harness for chafing, pin damage, corrosion or aftermarket splices
With ignition off, measure voltage at the underhood lamp connector pins (expect ~0V or open when off; seeing battery ~12V indicates short to battery)
Disconnect the lamp connector and re-check the output voltage at the module/harness side to determine if short is in lamp/connector or upstream in harness/module
Check related fuses and fusible links for correct rating and evidence of overheating
Perform a parasitic draw test if battery drain is suspected

Signal parameters

Expected OFF voltage at lamp output: approximately 0 V (open) / low impedance to module ground control
Expected ON voltage at lamp output: battery voltage (~12.0–14.5 V) when switched on
Typical current draw: depends on lamp type — incandescent lamps may draw several hundred mA; LEDs usually draw
If shorted to battery, output will show continuous ~12 V when lamp should be off

Diagnostic algorithm

Retrieve all related DTCs and vehicle-specific data; note conditions when DTC set (hood position, ignition state).
Visually inspect lamp assembly, connector, and wiring looms for damage, corrosion, or aftermarket splices; repair obvious damage.
With ignition off, disconnect the underhood lamp connector. Clear codes, then cycle hood/ignition to see if DTC returns. If no return, fault likely in lamp/connector.
Measure voltage at the lamp connector (harness side) with connector disconnected: - If ~12 V when it should be off, there is a short to battery upstream (harness or module). - If ~0 V, reconnect and measure at lamp side; if lamp is shorted, it will pull the circuit.
Check continuity between the lamp output pin and battery positive (fused circuits) with ignition off; continuity indicates a short/backfeed. Also check continuity to ground to rule out short to ground.
Isolate sections of harness (disconnect other downstream connectors, remove body panels) to locate the short. Use a fused jumper or current-limited bench supply when probing to avoid damage.
If harness and lamp test good and short remains at module output, suspect internal BCM/body control module failure; verify power/ground/relevant inputs and replace module only after confirming harness is not shorted.
After repair, clear codes and verify normal operation across multiple cycles and that no parasitic drain remains.

Likely causes

Chafed harness where lamp feed contacts a battery hot feed or fused hot cable
Connector corrosion at lamp or junction causing bridging to battery feed
Lamp assembly wiring shorted to constant hot (e.g., fused accessory circuit)
BCM/output driver failed closed and sourcing battery voltage

Fault status

⚠️ Status

Body module detected underhood lamp output is shorted to battery voltage (output is seeing constant battery feed or an internal short to B+). This can cause the lamp to remain on, blow fuses, or create parasitic battery drain. Investigation of lamp, harness and module required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours