C1225

Code

Generic C — Chassis

Lamp Brake Warning Output Circuit Short To Battery

Brand: Generic

Type: C — Chassis

Views: UK: 30 EN: 63 RU: 37

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Page language: EN

Causes

Damaged or chafed wiring in the brake warning lamp output circuit creating a short to battery
Corroded or bridged connector or socket at the instrument cluster or lamp assembly
Failed brake-warn lamp bulb or LED driver internally shorted to battery
Stuck/shorted relay or fused feed providing battery voltage to the output when it should be open
Faulty body control module (BCM) / ABS module or internal driver transistor failure
Aftermarket accessories improperly wired into the lighting circuit

Symptoms

Brake warning lamp (and possibly related warning indicators) illuminated continuously
Brake warning lamp does not respond to ignition or brake switch changes (stays on)
Intermittent or constant battery drain in some cases
Possible multiple related warning lamps if BCM shares circuits

What to check

Retrieve freeze frame and stored codes from BCM/ABS/instrument cluster and note occurrence conditions
Perform visual inspection of instrument cluster connector, fuse box, lamp sockets, and visible wiring harnesses for damage or corrosion
Check for aftermarket devices connected to lighting or brake circuits
With ignition ON, measure voltage at the brake-warn output pin at the controlling module and at the lamp connector
Disconnect the lamp/cluster connector and see if code clears or voltage changes to isolate load vs driver issue
Inspect and test related fuses and relays for stuck contacts

Signal parameters

Expected: With circuit inactive, driver output should be open/low (approx. 0–1 V) or high-impedance; with lamp commanded ON it should present battery voltage (~11–14.5 V) through lamp load
Fault present: steady battery voltage (~12 V) measured at the output when lamp should be OFF
Typical lamp load: incandescent filaments show low resistance (~1–30 Ω depending on bulb); LED modules may show higher or electronic loads — consult vehicle wiring diagram

Diagnostic algorithm

Read and record all stored codes and readiness status from BCM/ABS/instrument cluster.
Reproduce fault if possible and note when it occurs (key position, braking, doors, unlock).
Visually inspect wiring, connectors, and lamp sockets for damage, corrosion, or signs of shorting; repair as needed.
Disconnect the brake-warn lamp connector at the instrument cluster or lamp assembly. Clear the code and cycle ignition. If the code does not return, the short is in the wiring or lamp assembly downstream of the connector.
With connector disconnected and ignition ON, backprobe the module output pin. Measure voltage: if ~12 V with connector disconnected, the module output is being fed by battery (short) or the module driver has failed. If low/0 V with connector disconnected but rises when connector is attached, suspect lamp/connector or downstream short.
Isolate wiring by disconnecting intermediate connectors or removing lamp sockets until the short is localized. Use a fused jumper or test light to prevent damage during checks.
If wiring and lamp assembly are verified OK, replace or repair the controlling module per manufacturer procedure. Verify replacement resolves code.
After repairs, clear codes and perform road/operation test to confirm the fault does not return.

Likely causes

Shorted wiring or pin terminal at instrument cluster connector
Corroded lamp socket or passenger compartment connector causing positive feed to appear on the output circuit
Faulty instrument cluster/BCM output driver (replace only after wiring is verified)
Bulb or LED module failure with internal short

Fault status

⚠️ Status

Brake warning lamp output circuit short to battery detected — the output is seeing battery voltage when it should be off. Inspect wiring, connectors, lamp(s), and controlling module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours