New Holland UCM 1522 – UCM: Left Brake Light Actuation: Short to Ground

The control module has detected that the electrical circuit responsible for actuating the left brake light is shorted to ground. This means the voltage intended to illuminate the left brake light is finding an unintended path to the machine's chassis (ground) before reaching the bulb/LED, or the component itself has failed internally. This will typically cause the left brake light to fail to illuminate and may blow a corresponding fuse.

• L213
• L215
• L218
• L220
• L221
• L223
• L225
• L228
• L230
• L234
• C227
• C232
• C234
• C237
• C238
• SR130
• SR175
• SV250
• TR270

1. 1

   Visually inspect the left rear tail light assembly for physical damage, cracked lenses, or water intrusion, which commonly causes internal shorts.

2. 2

   Inspect the main fuse and relay panel for blown fuses or relays with burnt pins related to the lighting circuit.

3. 3

   Perform a harness isolation test by disconnecting the pigtail connector at the left brake light and using a digital multimeter to check for continuity to ground on the power supply wire. If the short to ground is still present with the light unplugged, the wiring harness is chafed or pinched; if the short disappears, the tail light assembly itself is internally shorted.

1. 1

   Safely Secure the Machine

   Park the machine on a level surface, lower the boom completely (or engage the mechanical boom locks if it must be raised), and turn off the ignition.

2. 2

   Disconnect Power

   Disconnect the negative battery cable to prevent electrical spikes or further damage to the UCM during repair.

3. 3

   Access the Left Brake Light

   Locate the left rear tail light assembly and disconnect its electrical connector.

4. 4

   Address the Short

   If the light is faulty: Unbolt the damaged tail light housing from the machine frame and install the replacement assembly. Plug the connector back in. If the harness is faulty: Trace the wiring harness from the left rear corner back toward the cab/UCM. Look for pinch points, rubbed insulation, or exposed copper touching the metal chassis. Cut out the damaged section of wire, solder in a new connection, and seal it thoroughly with marine-grade heat shrink tubing.

5. 5

   Reassemble and Test

   Reconnect the negative battery cable. Turn the ignition key to the ON position and test the brake lights.

6. 6

   Clear Codes

   If the code does not move to an "inactive" status automatically upon fixing the short, use a diagnostic service tool to clear the DTC from the UCM memory.