True T-series Error Codes
Applies to: T-series and GDM reach-ins. Compiled and paraphrased from True's own installation manuals, including the GDM and T-Series Scientific manual TEC_TM_288 (part 889161, Rev A), which prints the LAE display code table and alarm behavior, plus True controller documentation for Dixell equipped models. The same fault carries different labels across controller generations; always confirm against the documentation for your exact model. THE DIXELL ROWS ARE ANCHORED TO DIXELL'S OWN ELECTRONIC CONTROLS HANDBOOK, published by Dixell S.p.A., now an Emerson brand, on the reasoning that the controller's maker is the authority on its own codes and documents the whole set rather than the subset a cabinet manufacturer chose to reprint. That is where the compressor duty-cycling behaviour behind P1 comes from, along with the 000 and CCC distinction, dEA, the three external alarm severities and the probe-count configuration warning, none of which appear in the cabinet documentation. Table last updated Aug 16, 2026.
How to read the codes
True units speak two code dialects depending on which controller the model carries. LAE-controlled models (T-23, select T-49, TFP, TPP, TSD, TSSU, TWT, and GDM-26/49/69-HC glass door merchandisers) show E-codes and lowercase text codes like thi, tLo, and do. Dixell-controlled models (T-49, TAC-48, TAC-48GS, TAC-72RC) show P-alarms and HA/LA for the same faults. Identify your controller before matching a code.
The codes
| Code | Meaning | Likely causes | Operator-safe steps | Technician work |
|---|---|---|---|---|
| E1 / P1 | Cabinet temperature probe failure | Thermostat probe or its wiring, per Dixell's own handbook. THE BEHAVIOUR MATTERS MORE THAN THE CAUSE and it is the reason this fault gets missed: when a probe fault is detected the display flashes P1 and the controller AUTOMATICALLY CYCLES THE COMPRESSOR ON AND OFF on a fixed duty cycle set by parameters, instead of regulating to temperature. So the cabinet keeps cooling and may hold roughly the right temperature for a while, or drift badly, depending on load and ambient. It is running blind, not stopped. The thermostat probe reads invalid: failed thermistor or a disconnected wire at the controller | Do not treat a flashing P1 as cosmetic just because the box still feels cold. Put a thermometer in the cabinet and check the product, then call. Dixell notes probe alarms can be cleared by switching the controller off and on, which proves nothing if the probe is genuinely failed and will simply return | Thermistor resistance testing against the chart and replacement |
| E2 / P2 | Evaporator probe failure | Evaporator coil sensor fault, sometimes accompanying heavy frost or defrost problems | Check for visible ice buildup on the evaporator; record the code | Probe replacement and defrost system diagnosis |
| E3 / P3 | Auxiliary or display probe failure | Third probe circuit fault | Record the code for the technician | Probe testing and replacement |
| thi / HA | thi: highest temperature recorded in the LAE log. HA: live high temperature alarm on Dixell models | These are different things that get conflated. On LAE controlled models thi is a logbook entry, the maximum probe 1 temperature since the log was last reset, and True's manual says to reset it after the first 24 hours of operation and after any alarm. HA on Dixell controlled models is the active high temperature alarm: door left open, dirty condenser, failed evaporator fan, heavy warm product load, or a refrigeration side fault. | For thi: review the logged value, then reset the log per the manual so the next reading means something. For HA: confirm the door seals shut, clean the condenser, avoid loading warm product; move product if temperature does not recover. | For a real high temperature condition, refrigeration side diagnosis (EPA 608 required); the thi log itself is not a fault. |
| tLo / LA | tLo: lowest temperature recorded in the LAE log. LA: live low temperature alarm on Dixell models | tLo on LAE models is the logged minimum probe 1 temperature, a record and not an active alarm. LA on Dixell models is the live low temperature alarm: setpoint or control fault, or a stuck run condition. | For tLo: review and reset the log. For LA: check the setpoint and record the code. | Controller and probe diagnosis for a genuine low temperature condition. |
| do | Door open alarm | Door open, cracked, or not sealing: worn gasket or sagging hinges (LAE-controlled models) | Close the door fully; inspect the gasket and hinges | Door switch, hinge, and gasket service |
| hi | Cabinet high temperature alarm (LAE) | The internal temperature has risen past the alarm threshold, 45F (7C) by default on the Scientific models, adjustable per application. The control beeps and flashes hi; the high alarm also has a delay at initial startup so a fresh plug in does not false alarm. | Press any button to silence the beeps; the display keeps flashing hi until temperature recovers. Check the door, clear the condenser, and move product if it does not come back down. A silenced but unresolved alarm re-beeps for 20 seconds every 60 minutes. | Same diagnosis as any warm cabinet: condenser, evaporator fan, defrost operation, then sealed system (EPA 608 required). |
| Lo | Cabinet low temperature alarm (LAE) | Internal temperature below the alarm threshold, 36F (2C) default on the Scientific models: setpoint too low for the load, control or probe fault, or a compressor that will not cycle off. | Press any button to silence; verify the setpoint. Product at freezing risk in a cooler is worth a same day call. | Check probe placement and resistance, control cut in and cut out, and relay operation. |
| dEF | Defrost in progress (LAE) | Normal: the control initiates defrost on its programmed interval or on demand, and shows dEF while it runs. True's manual notes the display can briefly show dEF during a refrigeration cycle right after defrost, and temperatures read higher than normal during defrost. | Wait it out; dEF is not a fault. Only worry if the cabinet never returns to temperature afterward. | If dEF never terminates, check the defrost termination probe (t2 on CD25 controls) and the defrost parameters. |
| oFF | Controller in standby, refrigeration off (LAE) | Someone held the cancel or power key: the control deactivates the refrigeration system and connected components. Lights stay powered, which makes the cabinet look on while it slowly warms. | Press and hold cancel until the display shows on. If your True reads oFF and the product is warm, this is why. | No fault to diagnose; confirm nobody is using standby as a light switch. |
| Loc | Keypad locked (LAE) | The keypad lock is engaged; the control also relocks itself after a period of inactivity. | Unlock per the manual for your control face: on the standard control, press info, arrow down to Loc, hold info and change the setting with the arrows. On CD25 controls, hold confirm 5 seconds, then set Loc to no. | Same procedure; a keypad that will not unlock is a control replacement. |
| 000 and CCC (Dixell controllers) | Probe open circuit and probe closed circuit respectively | Dixell's own handbook distinguishes these from P1 and P2: 000 is an open circuit and CCC a short. Where P1 says the probe reading is unusable, these say which way it failed, which is what decides whether you are looking for a broken wire or a pinched one | Nothing to try. Record which of the three is showing, because they are not interchangeable | Open versus short narrows the fault before the panel comes off |
| dEA (Dixell controllers) | Defrost ended on TIME rather than on temperature | Not a failure, and the best early warning this controller gives. A defrost is supposed to end when the evaporator reaches temperature; ending on the timeout means it did not get there. Ignore it and the next complaint is ice | Report it before anything ices up. This is the code that lets you fix an icing problem before it becomes one | Evaporator probe position, defrost heater or hot gas, and airflow. Recurring dEA precedes an icing call |
| CA and EA and OFF (Dixell controllers) | External alarms of three severities, from a digital input | EA is a generic external alarm, CA is the Klixon external alarm, and OFF is a serious external alarm. They come from a device wired into the controller rather than from the controller itself. Dixell notes CA usually indicates incorrect installation, with common causes being no refrigerant, loose or incorrect wiring, or connection errors, so it appears most often on a recently installed or recently serviced cabinet | On a new or just-serviced cabinet, CA points back at the installation rather than at the equipment | Trace the digital input to whatever is wired to it before diagnosing the controller |
| FF and rtC and EE (Dixell controllers) | Power interruption during fast chill, clock settings lost, memory corruption | FF records that power failed during a fast chill or fast freeze cycle, which is a food safety question rather than an equipment one, because the cycle did not complete. rtC means the real time clock has lost its settings, which stops scheduled defrosts running correctly. EE is data or memory corruption in the controller | FF means check the product that was in the cabinet, not the cabinet | rtC is usually a battery. EE generally means the controller |
| Probe alarms straight after a service visit | Not a fault: the probe count does not match the configuration | Dixell's instruction is to connect the number of probes that suits parameter tC, and warns that failing to do so WILL cause probe alarms. A cabinet that alarms immediately after a controller swap or a probe replacement is usually configured for a probe count it does not have | If the alarm started right after somebody worked on it, say so when you call. It changes where they look first | Check tC against the probes actually fitted before condemning a probe |
If this needs a refrigeration technician
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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.