Garland MCO oven Error Codes
Applies to: MCO convection ovens. Compiled and paraphrased from Garland's own documentation: the Convection Oven Digital Control Probe Error Diagnosis Guide and the Garland service manual troubleshooting guide for the MCO ovens, published in the Garland Group document catalogue, together with the Garland Moisture+ service manual, part MPSM07, which supplies the HI TEMP threshold and behaviour, the HELP cause list and the 3-4-2-4 service code. NOTE ON SERIES: the HI TEMP, HELP and service-code rows are documented for the Moisture+ digital control. MCO ovens using the same digital control behave the same way, but MCO ovens are also sold with MANUAL controls that display nothing at all, which is why several rows in this table are symptoms rather than codes. Resistance values are Garland's published figures. Garland is a Welbilt brand; confirm against the manual for your exact model and control type. Table last updated Aug 16, 2026.
How to read the codes
Garland's digital convection controls show WORDS rather than numbered codes, and two of the words most often reported as faults are not faults at all. The controller reads oven temperature from the probe as a RESISTANCE, so the whole diagnosis turns on one ohms chart: 150F is 1143 ohms, 300F is 1553 ohms, 500F is 1949 ohms. Other Garland and US Range models show additional messages we have not reproduced here; this page covers the digital MCO control specifically.
The codes
| Code | Meaning | Likely causes | Operator-safe steps | Technician work |
|---|---|---|---|---|
| Probe Error | The control is receiving no signal at all from the temperature probe | Garland names five possible points, and they must be isolated in order: the probe itself, the probe harness, the relay board, the 15 pin control harness, or the main power control board | The oven will not heat and nothing an operator does will clear it. Note whether it appears the instant the oven is switched on, which is what an open probe circuit looks like | Garland's three-step isolation. Step 1, disconnect the probe leads at the relay board and compare against the ohms chart; if they do not match or read open, replace the probe and harness. Step 2, disconnect the 15 pin control harness at the relay board with the probe still connected and retest; open means replace the relay board. Step 3, reconnect and disconnect the far end at the main power control board; a correct reading there means the MAIN BOARD is at fault, open means the 15 pin harness is. Garland adds one warning worth heeding first: always check the 15 pin harness pins are properly seated |
| Auto | Not a fault. The oven has been switched off while still above 150F, and the fan is running it down | Normal cool-down behaviour. Above 150F, which is 1143 ohms at the probe, the fan relay stays closed and the display reads Auto | Nothing to do. This is the single most misread display on these ovens: the oven is off, the fan is protecting it, and it will stop by itself | If the fan runs with the cavity below 150F, suspect the probe or the fan relay rather than the control |
| Off | Not a fault. The oven is off and has cooled below 150F, so the fan relay has opened | Normal end of the cool-down sequence | Nothing to do | If the display reads Off while the cavity is still hot, the probe is reading low; check against the ohms chart |
| Unit will not heat, no error shown | Something upstream is blocking the heat circuit before the control reports a fault | Garland's own troubleshooting lists these IN ORDER: an open circuit on the UPPER DOOR SWITCH, incorrect gas pressure or gas turned off, a loose ribbon connection between boards, and no power to the smart board | The door switch being first is the useful part. Check the door is fully closed and latching properly, because these ovens will not heat with a door switch open, and a door that looks shut can still be holding the switch off | Door switch continuity with the door closed, then gas pressure, then the ribbon connection, then power at the smart board |
| Fan runs but the oven does not heat | The blower circuit is healthy and the heat circuit is not | Heating element or gas valve, high limit, probe, relay or control board | Worth reporting exactly this way, because a running fan tells the technician the door switch and blower circuit are working and narrows the job before they arrive | Element continuity or gas valve operation, high limit, then probe resistance against the chart, then the relay board |
| Blower stops when the door is opened | NOT A FAULT. This is a designed safety interlock | Garland's fail-safe design deactivates the blower once the door opens past a set point, so nobody can reach a spinning fan | Normal and deliberate. It also means an oven propped open will not circulate air, so do not expect it to cook or cool the way it does closed | If the blower does NOT stop with the door open, the interlock has failed and is a safety issue rather than a convenience one |
| Oven bakes unevenly or slowly with no message | Airflow or calibration rather than a component failure | Air panel or fan obstructed, overloaded racks, a drifting probe, or an incorrect offset | Check nothing is blocking the air panel at the back of the cavity and that racks are not overloaded. Convection depends on air moving, so a blocked panel produces exactly the symptoms of a failing element | Confirm probe resistance against Garland's chart before adjusting anything, since a drifted probe raises no error |
| Reading the probe against temperature | How to tell a good probe from a failed one without guessing | A probe that has drifted rather than failed outright will not raise Probe Error but will bake badly | If bakes are inconsistent and no error shows, ask the technician to check probe resistance against the chart rather than replacing the control | Garland's chart runs 932 ohms at 0F to 2123 ohms at 590F, in ten degree steps. Read the row for the hundreds and the column for the tens: 350F is 1654 ohms |
| HI TEMP | The oven is more than 50F above its setpoint, and the heaters have been cut | Garland's published threshold: when actual cavity temperature exceeds the set temperature by 50F the display shows HI TEMP and the alarm sounds. The behaviour that follows matters more than the message. THE FAN KEEPS RUNNING AND ONLY THE HEATERS ARE CUT, so the oven does not feel dead, it feels like it is working while refusing to hold temperature. Documented on Garland's Moisture+ digital control; MCO models with the same digital control behave the same way, so confirm against the manual for your control | Take the product out, the cavity is far hotter than it should be. Let the oven cool and see whether it holds setpoint on the next cycle. If HI TEMP returns, stop using it: a control that has lost temperature regulation is a burnt-product and a food-safety problem before it is a repair | Probe calibration first, then the heat contactor. A contactor welded closed produces exactly this: the control commands heat off, the heaters stay on, and the cavity climbs past setpoint until the 50F alarm trips |
| HELP | The control has a fault it cannot narrow down, and Garland lists three very different causes | Garland's own cause list for HELP is a faulty probe, a stuck motor centrifugal switch, or a gas valve or ignition system fault. Those are not variations of one problem, they are three unrelated systems, which is why HELP on its own tells a technician almost nothing and why the symptoms around it are the actual diagnostic | Note precisely what the oven is doing alongside the message: is the blower running, does it light at all, is it heating slowly or not at all. That observation is worth more to the technician than the word HELP | Work the three in order of cost: probe resistance against the chart, then the motor centrifugal switch, then the gas valve and ignition system |
| Diagnostic mode and heat test | How to make the oven prove whether it heats, rather than guessing | Garland's digital control has a service level reached by entering the code 3-4-2-4 on the numbered buttons. It offers a Heat Test, which displays actual cavity temperature and switches the heaters on so the reading can be watched climbing, and a Temperature Calibration routine | Not an operator procedure. Worth knowing it exists so you can ask whether it was run | Heat Test separates a control that is not calling for heat from a heat circuit that is not responding, which is the split that decides the whole diagnosis. Run it before replacing anything |
If this needs an oven technician
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Two questions worth reading before you ring anyone: what to do first when a code appears and how to tell whether it is yours to fix.
Garland is a Welbilt brand, and Welbilt runs one technical support line covering all of them. The number, and what they will and will not do for you, is worth reading before you ring: most will help a technician who is already on site and will not talk an operator through a repair.
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Related: the PM checklist that prevents the most common codes outright, and the operator guides for symptom-first diagnosis.
Not sure this is the right make? The lookup by code shows every make that uses a given code, and flags the ones that mean different things depending on the machine in front of you.