Pulse oximeters

Masimo Rad-5: troubleshooting and error codes

The ServiceForge knowledge base holds 29 documented symptoms for the Masimo Rad-5, with 39 ranked causes, 15 diagnostic checks with test points and expected values, and 7 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

No Sen or Sen Off displayed patient safety

Display shows No Sen or Sen Off message indicating sensor detection issue

Ranked causes

1. Defective sensor (common)
2. Faulty patient cable (occasional)
3. Oximeter board failure (occasional)

First check

Verify cable is connected with sensor attached

Test point: sensor connector
Expected: cable connected with sensor attached

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

No sensor displayed patient safety

No Sen or Sen Off message displayed on unit

Ranked causes

1. Sensor fault (common)
2. Patient cable fault (common)
3. Oximeter board fault (occasional)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

No sensor message displayed

Display shows 'No Sen' or 'Sen Off' message indicating sensor not detected

Ranked causes

1. Defective sensor (common)
2. Defective patient cable (common)
3. Oximeter board failure (occasional)

First check

Verify cable is connected with sensor attached

Test point: Sensor cable connection
Expected: Cable connected with sensor attached

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm condition but no audible alarm patient safety

Alarm condition detected but no audible sound

Ranked causes

1. Speaker fault (common)
2. System board fault (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Display missing segments

LCD or LED display is missing or not showing segments properly

Ranked causes

1. Display failure (common)
2. System Board malfunction (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Rad-5 will not turn off caution

Unit cannot be powered off using normal power control

Ranked causes

1. System Board malfunction (common)
2. Keypad malfunction (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unit will not turn off

Rad-5 cannot be powered off

Ranked causes

1. System Board failure (common)
2. Keypad failure (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

5V Voltage Supply Out of Range

System error detected with audible alarm and error code displayed. 5V supply voltage outside acceptable range.

Ranked causes

1. 5V power supply voltage out of specification (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm mute cannot be disabled patient safety

Pressing Alarm button once does not disable alarm mute or no audible alarm is heard

Ranked causes

1. Alarm button function or mute disable logic malfunction (unknown)

First check

Alarm mute disabled by pressing Alarm button

Test point: Alarm button and speaker
Expected: audible alarm heard after single Alarm button press

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm mute not functioning

Double-pressing Alarm Silence button does not mute alarm or yellow LED does not stay on steadily

Ranked causes

1. Alarm mute button logic or LED control malfunction (unknown)

First check

Alarm mute activates on double button press

Test point: Alarm Silence button and yellow LED
Expected: momentary beep heard with yellow LED on and steady (not flashing)

1 more check with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm not functioning patient safety

No audible alarm or SpO2 display is not flashing when alarm should trigger

Ranked causes

1. Alarm circuit or speaker malfunction (unknown)

First check

Verify audible alarm occurs and SpO2 flashes when alarm threshold reached

Test point: Speaker output and display
Expected: audible alarm with flashing SpO2 display

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm Silence button not responding

Alarm does not silence when Alarm Silence button is pressed, or yellow LED does not flash

Ranked causes

1. Alarm Silence button or LED circuit malfunction (unknown)

First check

Alarm silences and yellow LED flashes on single button press

Test point: Alarm Silence button and yellow LED
Expected: alarm silenced with yellow LED flashing

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm silence timeout not working patient safety

Audible alarm does not resume after 120 seconds when Alarm Silence is active

Ranked causes

1. Alarm timeout timer malfunction (unknown)

First check

Alarm silence timeout at 120 seconds

Test point: Alarm output and yellow LED
Expected: audible alarm reactivates and yellow LED turns off after 120 seconds

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Battery Voltage Out of Range

System error detected with audible alarm and error code displayed. Battery voltage outside acceptable range.

Ranked causes

1. Battery voltage out of specification (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Blue Voltage Supply Out of Range

System error detected with audible alarm and error code displayed. Blue wavelength LED supply voltage outside acceptable range.

Ranked causes

1. Blue wavelength supply voltage out of specification (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

MS-X Board Failure

System error detected, main software triggers audible alarm and displays error code on handheld display. MS-X board held in reset, no runtime functionality available until power cycled.

Ranked causes

1. MS-X Board malfunction (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

No numeric display or Signal IQ bar pulsing

Display does not show numeric readings or Signal IQ bar is not pulsing after Masimo Set Tester connection

Ranked causes

1. Device not initialized or tester not properly connected (common)

First check

Verify display shows numeric readings and Signal IQ bar pulsing

Test point: Display output
Expected: numeric readings visible and Signal IQ bar pulsing within 20 seconds

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

No sensor detected or sensor off displayed

Display shows 'No Sen' or 'Sen Off' message indicating sensor detection failure

Ranked causes

1. Sensor failure or disconnection (common)

First check

Verify cable is connected with sensor attached

Test point: Sensor cable connection
Expected: Cable connected securely with sensor attached

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

No Sensor or Sensor Off displayed patient safety

Display shows "No Sen" or "Sen Off" message indicating sensor disconnection or failure

Ranked causes

1. Sensor fault or disconnection (common)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pulse rate measurement out of range

Pulse rate reading is not between 55 bpm and 65 bpm when Masimo Set Tester is connected

Ranked causes

1. Device malfunction or incorrect tester connection (unknown)

First check

Verify pulse rate measurement within specification

Test point: Display numeric reading
Expected: between 55 bpm and 65 bpm, +10 bpm

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pulse volume control not responding

Up and down arrows do not change pulse beep volume or volume cannot be silenced

Ranked causes

1. Volume control buttons or audio circuit malfunction (unknown)

First check

Up arrow increases pulse beep volume

Test point: Up arrow button and speaker output
Expected: audible increase in pulse beep volume

2 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Red Voltage Supply Out of Range

System error detected with audible alarm and error code displayed. Red wavelength LED supply voltage outside acceptable range.

Ranked causes

1. Red wavelength supply voltage out of specification (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Speaker alarming loudly

Speaker producing very loud alarm, unit not functioning or displaying

Ranked causes

1. Watchdog error (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Speaker alarming loudly and unit not functioning

Speaker produces very loud alarm, unit does not function or display information

Ranked causes

1. Watchdog error (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Speaker alarming loudly and unit not functioning or displaying patient safety

Speaker emitting very loud alarm; unit does not function or display information

Ranked causes

1. Watchdog error (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Speaker alarming very loud and unit not functioning caution

Speaker outputs alarm at high volume; unit does not function or display information

Ranked causes

1. Watchdog error (unknown)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Speaker alarming very loud and unit not functioning or displaying

Speaker produces very loud alarm; unit does not function or display any information

Ranked causes

1. Watchdog error (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Speaker alarming very loudly and unit not functioning or displaying

Speaker produces loud alarm while device is non-responsive and display is blank

Ranked causes

1. Watchdog error (common)

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

SpO2 measurement out of range

SpO2 reading is not between 79% and 84% when measured with Masimo Set Tester

Ranked causes

1. Sensor or measurement circuit malfunction (unknown)

First check

Verify SpO2 measurement within specification

Test point: Display SpO2 value
Expected: between 79% and 84%, +5%

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Error codes

Code	Meaning	Trigger	Severity
`1`	MS-X Board Failure	System error detection during operation	error
`2`	MS-X Board Communication Failure	System error detection during operation	error
`3`	5V Voltage Supply Out of Range	System error detection during operation	error
`4`	Red Voltage Supply Out of Range	System error detection during operation	error
`5`	Blue Voltage Supply Out of Range	System error detection during operation	error
`6`	Battery Drop Voltage Out of Range	System error detection during operation	warning
`7`	Battery Voltage Out of Range	System error detection during operation	warning

Likely causes and actions for each code are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.