What causes Haas alarm 91?

TSC pump motor failure or pump impeller damage preventing pressure buildup in the coolant delivery system. Clogged coolant filter restricting flow and preventing adequate pressure from reaching the pressure switch sensor. Pressure switch itself has failed, is out of calibration, or has contaminated contacts preventing proper signal to MOCON. Air leak in TSC plumbing between pump discharge and spindle drawbar allowing pressure to escape before reaching the switch. Faulty wiring or loose connection between pressure switch and MOCON board input pin causing intermittent or no signal.

How do I fix Haas alarm 91?

1. Step 1: Check coolant tank level and verify TSC pump is running when M08 or TSC command is issued, listen for pump motor operation 2. Step 2: Access Diagnostics page and monitor the TSC pressure switch input status while manually triggering pump to verify signal reaches MOCON 3. Step 3: Inspect and clean or replace the TSC coolant filter cartridge, check for debris or contamination restricting flow 4. Step 4: Remove pressure switch and test with shop air or manual pump to verify it closes at rated pressure, replace if defective 5. Step 5: Inspect all TSC plumbing connections from pump to spindle for leaks, loose fittings, or damaged tubing allowing pressure loss 6. Step 6: Trace wiring from pressure switch back to MOCON connector, check for damaged insulation, loose pins, or corrosion at termination points and repair or replace harness as needed

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Haas Controller

Coolant · Basic · 45-90 minutes

Alarm 91

Battery Dead

Haas Alarm 91 fires when the coolant pressure switch (typically connected to input M14) detects pressure below the minimum threshold set in Parameter 378 (COOLANT PRESSURE). The NGC control monitors this input continuously during machining operations and will immediately halt the program when insufficient pressure is detected.

HaasCoolantBasic45-90 minutes

91

Battery Dead

Coolant System Pressure Low

Root Cause Summary

Haas Alarm 91 fires when the coolant pressure switch (typically connected to input M14) detects pressure below the minimum threshold set in Parameter 378 (COOLANT PRESSURE). The NGC control monitors this input continuously during machining operations and will immediately halt the program when insufficient pressure is detected.

Safety

Never attempt to unblock nozzles or hoses while pump is running
Coolant fluid can be hot and cause burns, allow system to cool first
Ensure spindle is completely stopped before accessing coolant system

Causes and Fixes

1
Check Coolant Tank Level
Visually inspect coolant tank level through sight gauge. Minimum level should be above pump intake.
Ensure machine is in EMERGENCY STOP before opening any coolant system components.
2
Verify M14 Input Status
Navigate to CURRENT COMMANDS > DIAGNOSTICS > INPUTS and check M14 status. Should show ON when pressure is adequate.
M14 input toggles immediately when pressure threshold is crossed - use this for real-time monitoring.
3
Refill and Test System
Add appropriate coolant mixture, cycle coolant pump using M08 command, and verify pressure recovery on diagnostics screen.

DIY Feasiblehigh confidence

Call a technician if:

·Pump motor replacement required
·Parameter modifications needed
·Electrical troubleshooting beyond basic checks

Prevention

Regular coolant filter replacement every 3-6 months
Maintain proper coolant mixture ratio
Weekly coolant level checks
Annual pressure switch calibration

Common Mistakes

Disabling Parameter 378 instead of fixing root cause
Using wrong coolant mixture affecting pump performance
Ignoring early signs of pump wear
Not checking M14 input status during troubleshooting

Related Alarms

92 93 94

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