Introduction
Traffic signal controllers can develop recurring electrical, communication or configuration faults. Understanding the symptoms supports systematic diagnosis. This guide outlines fault checks; the applicable procedures and fault codes depend on the selected model and maintenance manual.
The Six Common Failure Modes
| Symptom | Likely cause | First test |
|---|---|---|
| Cabinet dark, no LEDs | AC mains lost or breaker tripped | Voltmeter at AC input terminals |
| All phases flashing red | Conflict monitor (MMU) fault or voltage sense lost | MMU diagnostic page |
| One phase maxes out, no service | Detector failed or detector card slot empty | Check detector calls on diagnostic |
| Phase sequence wrong | Recent reprogramming or cabinet swap | Compare to as-built timing plan |
| Random restarts | Surge damage, brown-out, bad battery | Check log for voltage dip events |
| Communication lost | Antenna, SIM, or central software mismatch | Ping controller from central |
The 15-Minute Field Diagnostic
Walk through this sequence on any failed cabinet:
1. AC mains: voltage at the service panel, breaker position, neutral-to-ground voltage.
2. DC bus: 24 VDC and 12 VDC bus voltages under load.
3. MMU state: current fault code on the MMU display.
4. Detector calls: presence indication on each phase when a vehicle is over the loop.
5. Conflict programming: jumpers match the intersection geometry chart.
6. Recent events: pull the last 50 events from the controller log.
7. Software version: confirm firmware matches the released version.
8. Backup battery: if the cabinet has one, check voltage and load test.
Eight checks. Most field failures resolve on step 3, 4 or 5.
When to Replace vs Repair
Replace the controller if:
– The firmware is end-of-life and cannot be updated.
– The conflict monitor trips on a known-good configuration.
– Multiple input or output channels have failed simultaneously.
Repair (replace board, fix wiring, restore settings) if:
– A single channel has failed.
– The MMU is reporting a recent voltage sense glitch.
– The detector card or surge arrestor is the only failed part.
Featured Products
GAOQIAO supplies traffic signal controllers with built-in diagnostic web pages, wired controllers with replaceable detector cards, and field troubleshooting guides.
Conclusion
Use the eight checks as a diagnostic framework, following the selected controller’s maintenance manual. Available test points, web access and fault-code explanations require model-specific confirmation. Remote diagnostic assistance, its scope and timing must be agreed; no fixed diagnosis time is guaranteed.
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Frequently Asked Questions
What is the most common controller failure?
Power-related: a surge arrestor that has failed short, drawing the cabinet into brown-out. Always check the AC and DC bus voltages first.
Can a controller be repaired in the field?
Most field issues are resolved by replacing a board (detector card, surge arrestor, output card) and restoring settings from backup. The controller itself rarely needs replacement.
How long should a controller last?
10-15 years is typical. Power supplies and surge arrestors may need replacement at year 8-10; the main CPU and conflict monitor usually last the full life.
Relevant GAOQIAO products
These public GAOQIAO catalogue pages are related to the guide. Open them for the representative description, then confirm the latest drawing and configuration before ordering.
- Traffic signal controllersWired and solar controllers with 6, 22, 44 and 56 output options.
- LED traffic signal heads200mm, 300mm and 400mm signal heads with MUTCD, EN12368, GB14886 compliance.
- Signal polesVertical, signal arm and double-arm poles for any intersection geometry.
- Spare parts and accessoriesSpare LED modules, lenses, visors, surge arrestors and anchor bolts.