Toshiba EC 8502 Alarm: Injection Pressure Limit Exceeded — Troubleshooting
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-06-02
Toshiba EC 8502 triggers when the injection pressure measured at the nozzle tip transducer exceeds the set limit value for more than 0.5 seconds. This is a protective alarm — the machine stops the cycle to prevent mold damage from excessive...
Toshiba EC 8502 triggers when the injection pressure measured at the nozzle tip transducer exceeds the set limit value for more than 0.5 seconds. This is a protective alarm — the machine stops the cycle to prevent mold damage from excessive injection pressure. Common causes: frozen gate (material solidified in gate before filling completed), blocked nozzle tip (contamination or degraded material), excessive injection speed setting relative to material viscosity, or a faulty pressure transducer providing incorrect readings.
Troubleshooting protocol: 1. Check actual pressure curve on the injection monitoring screen — compare peak pressure to the alarm threshold. 2. Verify nozzle temperature — if nozzle is 10-15°C below setpoint, material viscosity increases sharply, driving injection pressure up. 3. Purge the barrel through the nozzle into free air — if purge pressure is normal, the restriction is in the mold (blocked gate, insufficient venting). If purge pressure is high, the nozzle or check ring is the restriction point. 4. Verify the pressure transducer zero offset — transducer drift can cause false pressure readings.
Alarm Details
| Alarm Code | 8502 |
|---|---|
| Brand / Machine | Toshiba |
| Severity | High (Cycle Stop) |
| Component | Injection Unit / Pressure Transducer |
| Affected Systems | Injection Pressure Control |
Troubleshooting Protocol
Verify all electrical connections to the affected component. Check for loose wires, burnt connectors, or signs of arcing. Measure voltage at the component terminals.
Look for physical damage, corrosion, or wear. For heating bands: check for hot spots (discoloration). For sensors: check for damaged cables or contamination on the sensing surface.
For thermocouples: measure resistance (should be 2-10 ohms, not open circuit). For heating bands: measure resistance against the nameplate rating. For relays: test coil resistance and verify switching with a test signal.
Order the OEM replacement part (see OEM Parts table above). After replacement, run a full heat-up cycle and verify the alarm does not re-trigger. Document the replacement in the machine log.
OEM Replacement Parts
| Part Name | OEM Part Number | Est. Price |
|---|---|---|
| Toshiba Heating Band | TSB-HB-{zone} | $400-800 |
| Toshiba Thermocouple | TSB-TC-{zone} | $100-220 |
| Toshiba Injectvisor Controller | TSB-VIS-CTRL | $1,200-2,500 |
Prices are estimated US market ranges. Contact your OEM distributor for exact pricing. {zone} = zone-specific variant.
Same Alarm on Other Machine Brands
If you operate multiple injection molding machine brands, the same fault may appear under different alarm codes:
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Engel 405 Injection Pressure Limit |
Frequently Asked Questions
What causes intermittent 8502 alarms?
Intermittent 8502 alarms typically result from inconsistent material viscosity — check drying consistency (moisture analyzer), barrel temperature PID tuning, and regrind percentage variation. A worn check ring that seals inconsistently can also cause intermittent pressure spikes.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org