This article explains the possible causes and solutions to a Midmark M9-M11 New Style autoclave Error Code C660.

Midmark M9/M11 “NS” Error Code C660 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 C660. 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 POWER UP mode.

Causes, Checks and Actions 

Possible Cause 1: Power interruption. (Unit lost power for a few seconds during Fill, Heat-Up, or Sterilization Mode.) 
  • Check A: Check power cord connections. (Power interruption could be due to an electrical storm, brown out, etc.) 
  • Action A: Unplug unit for 60 seconds, then plug unit into a dedicated, properly rated circuit. 


  • Check B: Check supply voltage.
  • Action B: Contact an electrician to modify voltage. 

Possible Cause 2: The operator may have unplugged the unit when a previous error code was displayed. 
  • Check: Check previous error codes. Refer to: Service Diagnostics (Recall Errors) 
  • Action: Refer to the error code(s) in this troubleshooting chart.

Possible Cause 3: 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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