Conflict Monitor Lockout After a Storm

The conflict monitor is a fail-safe device. It continuously compares the controller's green and walk outputs and removes power from the controller's output circuits when it detects an incompatible combination, such as green on phase 2 and green on phase 4. When it trips, the signal goes to flashing mode and the monitor latches the fault so that the condition cannot be silently restored.

Pressing reset without diagnosis would clear the latch but would not remove the cause. If the 2-4 green condition is real, resetting would put two conflicting movements back on green at 120 VAC, creating an immediate collision risk. The presence of 120 VAC on both the phase 2 and phase 4 green inputs at the monitor terminals while the controller is supposed to be in flash points to either a field wiring short, a welded output relay, or a backplane/harness short. The water staining and the power-loss event also suggest surge or moisture damage. The correct first action is to keep the intersection in flash, protect the work area, and diagnose before any reset.

Keep the signal in flashing mode and use appropriate traffic control and personal protective equipment. Then isolate cabinet from field before resetting anything.

1. Record the monitor event log and note the fault type, channels, and time stamps; photograph the display and the water staining.
2. Verify the monitor's configuration against the intersection's phase plan - an incorrect program card or channel assignment can produce a false conflict indication.
3. Measure voltage at the monitor terminals for phases 2 and 4 green with a true-RMS meter; confirm the 120 VAC reading and check for voltage on other conflicting channels.
4. Separate cabinet from field. Disconnect the field green leads for phases 2 and 4 at the terminal block and recheck the monitor terminals. If the conflict disappears, the fault is in the field; if it remains, the fault is in the cabinet, backplane, harness, or monitor.
5. Inspect for moisture and damage in the cabinet, junction boxes, and signal heads; water in a splice can bridge conductors.
6. Check the controller output relays and the monitor harness for welded contacts, loose pins, or burned insulation.
7. Substitute a known-good monitor or test box only after isolation to confirm whether the monitor itself is faulty.

Do not reset the monitor until the source is found and corrected.

Return to stop-and-go only after the fault is located, corrected, and the affected circuits have been tested. The specific conditions are:

• The real or apparent 2-4 conflict has been eliminated; if field wiring was shorted, the damaged conductors and splices must be replaced and meggered or insulation-tested as appropriate.
• Any water intrusion has been corrected and the cabinet, backplane, and harness have been dried and inspected for corrosion.
• The monitor is confirmed to be correctly programmed and is not itself defective; if replaced, the replacement must match the intersection's phase and channel configuration.
• All controller outputs have been checked for welded relays or false voltages, and a full flash test and conflict test have been performed.
• The monitor has been reset with the correct procedure, and the signal has been observed through several complete cycles before being left in automatic operation.

Complete an MMU event-log download, a maintenance and repair report describing the cause and corrective action, the test results, and an updated cabinet wiring/as-built record. Notify the responsible agency and update the signal-file history so the next responder knows a conflict lockout occurred.