This article explains the possible causes and solutions to a Midmark M9-M11 New Style autoclave Error Code C661.

Midmark M9/M11 Error Code C661 Leave a comment

In this article, we’re going to explain one of the many error codes that can affect your Midmark M9/Midmark M11 autoclave. This article will focus specifically on error code C661. We’ll tell you about the problem, what displays when the error occurs, its possible causes, and the course of action to take to resolve said error.

However, if you’re more of a visual learner, we have a video on this error code available here.




Pressure A/D converter reports an average value outside the limits for normal operation during SELECT mode.

Causes, Checks and Actions

Possible Cause 1: Temperature sensor malfunctioning. 
  • Check A: Check for residue build up on temperature sensor probe. 
  • Action A: Clean sensor probe with Speed-Clean, distilled water, and abrasive pad. 

Speed Clean available here.

  • Check B: Check that nothing is touching or crowding the temperature sensor. (Example: trays, pouches, cassettes, etc.) 
  • Action B: Reposition items so nothing touches or crowds the temperature sensor. 


  • Check C: Perform: Temperature Sensor Resistance Test. Allow sensor to cool to room temperature before testing. Acceptable range 1.07-1.1K Ω. Refer to: Temperature Sensor Resistance Test 
  • Action C: Replace temperature sensor. 

M9 Temperature Sensor available here

M11 Temperature Sensor available here. 

  • Check D: Perform: Temperature Sensor Supply Voltage Test. Disconnect sensor harness from J12 on PC board. On pins 1 & 2 acceptable range is 4.0 – 6.0 VDC. Refer to: Temperature Sensor Supply Voltage Test 
  • Action D: Replace Main PC board.

M9 PC Board OEM available here

M11 PC Board OEM available here

Possible Cause 2: PC Board malfunctioning. 
  • Check 1: Perform: Heating Element Supply Voltage Test (With harness attached to leads should have line voltage in test mode) 
  • Check 2: Perform: Main PC Board Relay Test (Check TP1 & TP2 for an acceptable range: 10 to 14 VDC) 
  • Check 3: Perform: Main PC Board Pressure Transducer Voltage Test (Acceptable range: 4.0 to 6.0 VDC) 
  • Action: Replace Main PC board. 

M9 PC Board OEM available here

M11 PC Board OEM available here

As always if you have any questions about this process or anything else please feel free to contact us and take advantage of our “FREE TECH SUPPORT.”

We also offer FREE VIRTUAL TECH SUPPORT to “See and Talk” with a “Real Time Live Technician” for any problems you may be in need of help with.

You can also use our “FREE MAINTENANCE PROGRAM. Take the guesswork and worrying about what unit is due for maintenance and which maintenance cycle it is time for. We will keep track of all your autoclaves and let you know when it’s time for anything.

The Midmark M9 autoclave is available here. 

We also have the Midmark M11 autoclave here. 

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