Pulse oximeters

Nellcor Oxi-Max N-595: troubleshooting and error codes

The ServiceForge knowledge base holds 22 documented symptoms for the Nellcor Oxi-Max N-595, with 44 ranked causes, 52 diagnostic checks with test points and expected values, and 81 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Alarm does not sound patient safety

Alarm is silent when expected to sound

Ranked causes

1. Alarm silenced or disabled (common)
2. Speaker connection loose (common)
3. Speaker defective (occasional)
4. User Interface PCB defective (occasional)

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

Battery Low indicator lights steadily on AC with battery not discharged

Battery Low LED illuminates despite AC connection and adequate battery charge

Ranked causes

1. AC outlet not operational or unplugged (common)
2. Blown fuses (common)
3. Power supply defective (occasional)
4. Harness connection fault (occasional)

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

Battery does not charge

Battery fails to charge when connected to AC power

Ranked causes

1. Battery aged beyond 2 years (common)
2. Battery unable to hold charge (common)
3. Power supply output voltage or current incorrect (occasional)

First check

Determine battery age

Test point: Battery
Expected: Battery less than 2 years old

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Display pixels do not light

LCD display is dark or pixels are not illuminating

Ranked causes

1. Display PCB connection loose (common)
2. Display PCB defective (occasional)
3. User Interface PCB defective (occasional)

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

Display values missing or erratic

Displayed readings are incomplete, intermittent or unstable

Ranked causes

1. Pulse oximetry cable faulty (common)
2. OXIMAX sensor damaged (common)
3. User Interface PCB defective (occasional)

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

No power-up on AC and/or DC

Monitor does not turn on when connected to AC or DC power

Ranked causes

1. Blown fuses in Power Entry Module (common)
2. Power supply defective (occasional)
3. Harness connection fault (occasional)

First check

Inspect fuses in Power Entry Module

Test point: Power Entry Module
Expected: Fuses intact and properly seated

1 more check with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

SpO2 or Pulse values change rapidly with erratic Pulse Amplitude

Readings fluctuate excessively and waveform indicator is unstable

Ranked causes

1. OXIMAX sensor damp or reused excessively (common)
2. Electrosurgical unit interference (occasional)
3. User Interface PCB defective (occasional)

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

Alarm sounds for no apparent reason

Audible alarm triggers without valid cause or trigger condition

Ranked causes

1. Moisture or spilled liquids in monitor (common)
2. User Interface PCB defective (occasional)

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

Battery Low error code with AC power disconnection

Monitor generates error when disconnected from AC power supply

Ranked causes

1. Battery discharged (common)
2. Battery defective (occasional)

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

Calibration: Alarm operation and silence function patient safety

Verify audible and visual alarm activation, silence button functionality, and timeout behavior

Ranked causes

1. Alarm system requires functional verification (common)
2. Alarm volume requires adjustment capability (occasional)

First check

Plethysmograph waveform tracking

Test point: Pleth display
Expected: Waveform tracks user pulse rate

12 more checks with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Power-on alarm limits patient safety

Verify and adjust default alarm limits for SpO2, pulse rate, and SatSeconds parameters

Ranked causes

1. Alarm limits require verification after repair or maintenance (common)
2. Factory defaults require confirmation after power cycle (common)

First check

SpO2 upper alarm limit minimum

Test point: LIMITS display
Expected: Minimum value 86 %

9 more checks with pass and fail actions, 6 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Monitor does not respond to button presses

Buttons pressed do not trigger any response or function

Ranked causes

1. User Interface PCB defective (common)
2. Top case assembly defective (occasional)

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

Pulse Amplitude indicator shows pulse but digital display shows zeroes

Pulse waveform indicator active but no numerical readings displayed

Ranked causes

1. OXIMAX sensor damaged (common)
2. User Interface PCB defective (occasional)

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

Battery charge verification

Charging battery to full capacity with monitor off or on

Ranked causes

1. Battery requires charging before use (common)

First check

Connect to AC power

Test point: AC power inlet
Expected: Monitor connected to AC power source

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

Battery Low alarm during DC operation with 15 minutes charge remaining caution

Low battery alarm sounds indicating 15 or fewer minutes of usable charge left

Ranked causes

1. Normal battery depletion at end of charge cycle (common)

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

Calibration: Analog output 1 volt BPM and Pleth

Verify analog BPM and Pleth output voltage at data port pins 13 and 14

Ranked causes

1. Analog BPM and Pleth outputs require calibration verification (common)

First check

Analog BPM and Pleth output voltage at pins 13 and 14

Test point: Data port pins 10 (negative reference) and 13, 14 (positive)
Expected: +1.0 VDC, ±0.025 VDC
Tools: Digital voltmeter

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

Calibration: Analog output 1 volt SpO2

Verify analog SpO2 output voltage at data port pin 6 relative to pin 10

Ranked causes

1. Analog SpO2 output requires calibration verification (common)

First check

Connect voltmeter to analog output

Test point: Data port connector pins 10 (negative) and 6 (positive)
Expected: Voltmeter connected with correct polarity

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

Calibration: Nurse call function RS-232

Verify RS-232 nurse call voltage output at data port pins 5 and 11

Ranked causes

1. RS-232 nurse call output requires verification (common)

First check

Connect voltmeter to data port

Test point: Data port connector pins 5 (negative) and 11 (positive)
Expected: Voltmeter connected with correct polarity

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

Calibration: Nurse call function solid state relay

Verify solid state relay nurse call output continuity between data port pins

Ranked causes

1. Solid state nurse call relay requires functional verification (common)

First check

Solid state relay pins 8-15 in alarm state

Test point: Data port pins 8 and 15
Expected: No continuity (≥1 megohm), ≥1 megohm
Tools: Digital voltmeter (DVM)

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

Calibration: Pulse tone volume control

Verify pulse tone volume adjustment and audibility range

Ranked causes

1. Pulse tone volume requires adjustment capability (common)

First check

Pulse tone volume increase

Test point: Monitor speaker
Expected: Pulse tone volume increases with ADJUST UP

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

Power-on self-test verification

Monitor LEDs, LCD pixels, backlight, speaker, and indicators during startup sequence

Ranked causes

1. Normal operation expected (common)

First check

All LEDs illuminate

Test point: Monitor front panel
Expected: All LEDs illuminated within 2 seconds of power-on

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

Unit does not power on high voltage

Monitor will not turn on or off; possible blown fuse in power module

Ranked causes

1. Blown fuse in power module (common)

First check

Inspect fuses in power module

Test point: Fuse drawer in power entry module
Expected: Fuses intact and rated 5x20-mm slow blow 0.5-amp 250-volt

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

Error codes

Code	Meaning	Trigger	Severity
`1`	SpO2 front end RAM error	Non-correctable failure detected	critical
`10`	Over-current limit in SpO2 front end has tripped	Non-correctable failure detected	error
`11`	SpO2 front end reports incorrect system voltage	Non-correctable failure detected	error
`12`	SpO2 front end reports other hardware problem	Non-correctable failure detected	error
`14`	SpO2 front end reports communication channel overflow	Non-correctable failure detected	error
`16`	SpO2 front end reports watch dog time out	Non-correctable failure detected	critical
`17`	SpO2 front end reports that sensor appears defective	Non-correctable failure detected	error
`18`	SpO2 front end reports internal register appears modified from expected value	Non-correctable failure detected	error
`19`	SpO2 front end reports signal out-of-range	Non-correctable failure detected	warning
`2`	SpO2 front end ROM/code integrity error	Non-correctable failure detected	critical
`256`	SpO2 back end reports beginning of packet missing	Non-correctable failure detected	error
`257`	SpO2 back end reports packet start ID (SID) missing	Non-correctable failure detected	error
`258`	SpO2 back end reports packet length error	Non-correctable failure detected	error
`259`	SpO2 back end reports message length error	Non-correctable failure detected	error
`260`	SpO2 back end reports packet contains unsupported Key	Non-correctable failure detected	warning
`261`	SpO2 back end reports packet CRC error	Non-correctable failure detected	error
`262`	SpO2 back end reports end of packet missing	Non-correctable failure detected	error
`263`	SpO2 back end reports packet contains undefined key	Non-correctable failure detected	error
`264`	SpO2 back end reports corrupted variable	Non-correctable failure detected	error
`265`	SpO2 back end reports memory overflow	Non-correctable failure detected	error
`266`	SpO2 back end reports bad pointer	Non-correctable failure detected	error
`267`	SpO2 back end reports parameter value out-of-range	Non-correctable failure detected	error
`268`	SpO2 back end reports reset detected	Non-correctable failure detected	warning
`269`	SpO2 back end reports unexpected value	Non-correctable failure detected	warning
`270`	SpO2 back end reports time-out	Non-correctable failure detected	error
`271`	SpO2 back end reports not ready/not initialized	Non-correctable failure detected	error
`272`	SpO2 back end reports double fault	Non-correctable failure detected	critical
`273`	SpO2 back end reports date out-of-range error	Non-correctable failure detected	warning
`274`	SpO2 back end reports incompatible software version	Non-correctable failure detected	error
`275`	SpO2 back end reports incorrect registration number	Non-correctable failure detected	warning
`276`	SpO2 back end reports sensor read failure	Non-correctable failure detected	error
`277`	SpO2 back end reports sensor signature verification fails	Non-correctable failure detected	error
`278`	SpO2 back end reports warmed sensor temperature set point failure	Non-correctable failure detected	error
`279`	SpO2 back end reports warmed sensor/SpO2 front end incompatible	Non-correctable failure detected	error
`280`	SpO2 back end reports does not support feature required by sensor	Non-correctable failure detected	warning
`281`	SpO2 back end reports overflow/underflow	Non-correctable failure detected	error
`282`	SpO2 back end reports sensor activation failure	Non-correctable failure detected	error
`3`	SpO2 front end reported a bad CRC	Non-correctable failure detected	error
`4`	SpO2 front end reported FSP message not allowed	Non-correctable failure detected	error
`48`	SpO2 front end reports spurious interrupt	Non-correctable failure detected	warning
`49`	SpO2 front end reports internal buffer overflow	Non-correctable failure detected	error
`5`	SpO2 front end reported illegal value sent in FSP message	Non-correctable failure detected	error
`50`	SpO2 front end reports intermittent error	Non-correctable failure detected	warning
`51`	SpO2 front end reports digital communications error	Non-correctable failure detected	error
`512`	General failure of UIF Module generic post / Dead battery/Missing battery	Non-correctable failure detected	critical
`514`	Real time clock is non-operational	Non-correctable failure detected	error
`515`	Application code is not present in the flash	Non-correctable failure detected	critical
`516`	Invalid flash type	Non-correctable failure detected	critical
`517`	Serial clock line is not toggling or is toggling at an incorrect rate	Non-correctable failure detected	error
`518`	Application program is corrupt	Non-correctable failure detected	critical
`519`	Invalid FE102 version	Non-correctable failure detected	error
`52`	SpO2 front end reports warmer error	Non-correctable failure detected	error
`520`	Error in the start up sequence	Non-correctable failure detected	error
`521`	OS multitasking service failure	Non-correctable failure detected	error
`522`	A state machine has received an unknown state transition	Non-correctable failure detected	error
`523`	Operation not completed successfully	User attempted operation failed	warning
`524`	Unexpected value received	Out-of-range parameter passed to function	warning
`525`	EEPROM CRC failure	Non-correctable failure detected	error
`526`	SpO2 module not responded	Non-correctable failure detected	error
`527`	Institutional parameters lost	EEPROM section CRC corrupt	warning
`528`	Current settings lost	EEPROM section CRC corrupt	warning
`529`	Critical low battery	Battery voltage critically low	critical
`53`	Front end data not received	Non-correctable failure detected	error
`530`	Low battery error	Battery voltage below acceptable threshold	warning
`531`	External watchdog failure	Non-correctable failure detected	error
`532`	Power PC watchdog failure	Non-correctable failure detected	critical
`533`	Boot NVROM uninitialized error	Non-correctable failure detected	error
`534`	Failed CRC check of application code in flash	Non-correctable failure detected	critical
`535`	Failed periodic ram CRC check on application code running in RAM	Non-correctable failure detected	error
`562`	SpO2 front end reset	Front end module reset detected	warning
`563`	SpO2 reported error	SpO2 module reported error condition	error
`564`	Clinical mode was exited after input was received	User exited clinical mode during operation	info
`565`	Communication failures between software modules	Module communication link failed	error
`566`	Excessive resets before UIF runs	Multiple resets occur during startup	error
`567`	Unexpected interrupt has been asserted	Interrupt from unidentified source	warning
`568`	General failure in UIF module generic post	Non-correctable failure detected	error
`569`	BOOT application program is corrupt - CRC does not match	Non-correctable failure detected	critical
`570`	RTC was restarted	Real-time clock reinitialized	info
`574`	Excessive restarts within 1 minute	Device restarted multiple times rapidly	error
`6`	SpO2 front end reports calibration (offset) failure	Non-correctable failure detected	error
`9`	SpO2 front end reported syntax error in FSP message	Non-correctable failure detected	error

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.