Blakeslee Conveyor Dishwasher Error Code M2: Prewash Probe Failure
M2 PREWASH PROBE FAILURE means the prewash probe has failed, and washing results may be affected. The manual says to contact Technical Service. A service technician should test the probe and its wiring.
Medium: washing results may be affected, but the cause is a sensor rather than a safety condition.
- Code
- M2
- Maker
- Blakeslee
- Equipment
- Conveyor dish machines
- Applies to
- RC-series rack conveyor with scrolling-text display and LED bar
What does Blakeslee error code M2 mean?
The prewash tank has a probe that reports water temperature to the control. If the signal is lost or implausible, the control displays M2 PREWASH PROBE FAILURE. The manual's meaning is a prewash probe failure and it notes that washing results may be affected. The instruction is only to contact Technical Service. The prewash section uses its temperature for loosening soil, and in this machine it has its own cooling function, which is reported separately under M3. A missing temperature reading therefore makes it harder for the control to manage the prewash as designed. The alarm names the probe, so the water supply and the heater are not necessarily the problem. It is the same kind of alarm as E2 on wash tank 1 but on the earlier stage of the machine.
Affected models and control systems
Blakeslee RC-series rack conveyor dishwasher. The PDF is Blakeslee's RC44 User Manual and prints no model name; the same alarm list appears in the RC62 manual.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- M2 PREWASH PROBE FAILURE on the display
- Prewash water temperature seems wrong
- Heavier soil left on dishes after the wash
- Alarm remains after a restart
Possible causes
Likely causes — what usually sits behind error code M2 on this control. A technician confirms which one it is before any part is replaced.
- Prewash probe open or shorted
- Probe lead damaged by heat or movement
- Probe connector corroded by moisture
- Control input not reading the prewash probe
Safe checks before calling for service
- Turn the machine off and on once to see whether M2 remains.
- If you continue to run, inspect finished dishes and rewash any that are not clean.
- Do not reach into the prewash tank.
- Keep the floor and area dry.
- Note the display and any other alarm shown with it.
How a technician diagnoses error code M2
- Read the alarm history and confirm M2 is active.
- Measure the prewash probe resistance at its connector with power locked out and compare with the water temperature.
- Inspect the lead and connector for damage and corrosion.
- Substitute a known resistance at the control input.
- Replace the probe, lead or board according to the result.
- The probe sits in a tank of wet, treated water close to wiring.
- Panels must come off to reach the connector.
- Separating a failed probe from a failed input takes a meter and a reference resistance.
How error code M2 differs from similar codes
M2 is the prewash probe. E2 is the same alarm for wash tank 1.
Technical reference
- Maker documentation
- Blakeslee owner support
- Edition
- COD. 4950E_U_USA, Ed. 00 - 09/2016
- Models / control
- RC-series rack conveyor with scrolling-text display and LED bar
- Section
- Chapter 12.2.1 Alarms description (pp. 54-55)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Blakeslee conveyor dish machine error codes
Does M2 stop the machine?
The manual says washing results may be affected, which means the machine may keep running with reduced control.
Is the prewash heater broken?
M2 names the probe, not the heater.
Why is the prewash temperature important?
It helps loosen soil before the main wash, so a blind control makes results less predictable.
Need help with Blakeslee error code M2?
A technician confirms the cause on site and gives you the price in writing before any work starts.