Thermo King Fault Codes

No Alarms Exist

Indicates the system is operating correctly and there are no active alarms.

Check Evaporator Coil Sensor (Zone)

The microprocessor has detected a failure or out-of-range reading in the evaporator coil sensor.

Check (Control) Return Air Sensor (Zone)

Failure of the return air sensor, responsible for measuring the cargo temperature.

Check (Control) Discharge Air Sensor (Zone)

Failure of the discharge air sensor, which measures the air leaving the evaporator toward the cargo.

Check Ambient Temp Sensor

The exterior ambient temperature sensor presents a reading failure.

Check Coolant Temp Sensor

Failure in the sensor that monitors the diesel engine coolant temperature.

Check Engine RPM Sensor

The system does not detect the engine rotation signal (RPM).

Unit Running on Coil Sensor (Zone)

The system is using the coil sensor to control temperature due to a main sensor failure.

High Evaporator Temperature (Zone)

An excessively high evaporator temperature has been detected.

High Discharge Pressure (or Temperature)

The compressor discharge pressure or temperature has exceeded safety limits.

Unit or Zone Controlling on Alternate Sensor (Zone)

The unit is controlling temperature based on a secondary or alternate sensor.

Sensor or Digital Input Shutdown (Zone)

A critical digital input or sensor has triggered a complete unit shutdown.

Sensor Check (Zone)

The microprocessor has detected an unusual discrepancy between temperature sensors.

Defrost Terminated by Time

The defrost cycle ended due to maximum time limit instead of temperature termination.

Check Glow Plugs or Intake Air Heater

Failure detected in the intake air heater or glow plug circuit.

Manual Start Not Completed

The operator did not complete the manual start sequence within the established time.

Engine Failed to Crank

The starter motor does not turn or the engine fails to rotate for ignition.

High Engine Coolant Temperature

The diesel engine has reached a temperature above the safety limit.

Low Engine Oil Pressure

The engine oil pressure is dangerously low.

Engine Failed to Start

The engine cranked but failed to stay running or did not reach ignition RPM.

Cooling Cycle Check (Zone)

The system detects insufficient cooling capacity during monitoring.

Heating Cycle Check (Zone)

The system detects insufficient heating capacity.

Cooling Cycle Fault (Zone)

Critical system failure preventing cooling; unit shuts down to protect cargo.

Heating Cycle Fault (Zone)

Critical failure preventing the unit from generating heat when required.

Alternator Check

System detects that the alternator is not charging the battery correctly.

Check Refrigeration Capacity (Zone)

Refrigeration capacity is lower than expected for the current setpoint.

Vapor Motor RPM High (CR)

Steam motor or electric compressor revolutions exceed the safety limit.

Pretrip or Self Check Abort

The diagnostic self-test (Pretrip) was canceled before completion.

Defrost Damper Circuit Check (Zone)

The circuit controlling the defrost damper exhibits a failure.

Defrost Damper Stuck Closed (Zone)

The evaporator damper has become stuck in the closed position.

Check Oil Pressure Switch

The microprocessor detected a discrepancy between actual oil pressure and the pressure switch status.

Refrigeration Capacity Low (Zone)

The unit or zone is not reaching the expected cooling capacity and has been stopped for safety.

Check Engine RPM

The engine speed sensor detects revolutions outside the configured range.

Check Modulation Circuit

The unit detected a problem in the modulation valve electrical circuit.

Check Run Relay Circuit

Failure detected in the run relay circuit, preventing unit operation.

Electric Motor Failed to Run

The backup electric motor does not start when standby mode operation is required.

Check Engine Coolant Level

The level sensor detects that the engine coolant is below the safe limit.

Electric Phase Reversed

The phases of the external power supply are reversed, which would cause inverse rotation.

Check Water Valve Circuit

Failure detected in the heating water valve control circuit.

Check High Speed Circuit

The microprocessor detected a failure in the circuit that activates engine high speed.

Check Engine Coolant Temp

Engine coolant temperature is unusually high or the sensor is failing.

Unit Forced to Low Speed

The unit has restricted operation to low speed to protect the engine or system.

Unit Forced to Low Speed Modulation

The unit is forced to low speed due to a limitation in the modulation system.

Check Fuel System

The system has detected problems in fuel supply or suction.

Check Hot Gas or Hot Gas Bypass Circuit

Electrical failure detected in the hot gas bypass circuit.

Check Air Flow (Zone)

Restriction detected in evaporator airflow in the indicated zone.

Remote Sensor Shutdown

Critical failure in a remote temperature sensor that prevents safe operation.

Check Belts or Clutch

A mechanical issue has been detected in the drive belts or the clutch.

Check Spare Sensor 1

Failure detected in auxiliary/spare sensor number 1.

Reset Clock

Microprocessor time and date have been lost or are invalid.

Check Shutdown Circuit

Failure detected in the engine safety shutdown circuit.

Check Heat Circuit (Zone)

System detected a problem in the components generating heat in the zone.

Check Economizer Valve Circuit

Failure in the economizer valve circuit affecting efficiency.

Test Mode Timeout

The unit remained in a test mode for longer than permitted.

Check Engine Speeds

Recorded engine speeds do not match expected calibration values.

Check Evaporator Fan Low Speed (Zone)

Failure detected in the evaporator fans' low-speed circuit.

Check Evaporator Fan High Speed (Zone)

A fault was detected in the high-speed circuit of the evaporator fans.

Low Battery Voltage

The battery voltage powering the microprocessor is too low.

Ammeter Out of Calibration

The system detected that the ammeter reading is out of range or inconsistent.

Engine or Vapor Motor Stopped

The diesel engine or electric motor stopped unexpectedly due to mechanical or fuel reasons.

Pretrip Reminder

Automatic reminder to perform a Pretrip inspection based on elapsed time.

Abnormal Temperature Differential (Zone)

Abnormal temperature differential detected in a specific zone (evaporator).

Low Engine Oil Level

The sensor indicates the engine oil level is below the safe limit.

Check Liquid Line Solenoid Circuit (Zone)

Fault detected in the liquid line solenoid circuit of a zone.

Internal Controller Fault Code

A technical error has been detected within the microprocessor or controller.

Hourmeter Failure

Hourmeter failure; controller is not receiving operating time data.

Hourmeter 4 Exceeds Set Time Limit

Maintenance hourmeter #4 has exceeded the configured time limit.

Hourmeter 5 Exceeds Set Time Limit

Maintenance hourmeter #5 has exceeded the configured time limit.

Hourmeter 6 Exceeds Set Time Limit

Maintenance hourmeter #6 has exceeded the configured time limit.

Controller Reset to Defaults

The controller has reverted to factory default settings due to an error or power loss.

Controller RAM Failure

Failure in the controller's RAM memory.

Controller EPROM Failure

Failure in the controller's EPROM memory.

Controller EPROM Checksum Failure

Software checksum error, indicating data corruption.

Data Log EPROM Failure

Failure in the data logger's EPROM memory.

Internal Data Logger Overflow

The internal data logger is full and cannot record more information.

Check Compressor Temp Sensor

Compressor temperature sensor circuit is out of range or faulty.

High Compressor Temp

The compressor temperature is unusually high, approaching the safety limit.

High Compressor Temp Shutdown

The unit stopped to protect the compressor due to excessive temperature.

Low Engine Coolant Temp

Engine coolant temperature is too low for normal operation.

Restart Null

The unit was unable to restart automatically after a nullified stop.

Forced Unit Operation

The unit is operating under a forced mode (manual or emergency).

Check Discharge Pressure Sensor

The controller detected an erroneous signal from the discharge pressure sensor.

Check Suction Pressure Sensor

The controller detected an erroneous signal from the suction pressure sensor.

Reserved for CR

Code reserved for specific Cargo Recording (CR) functions.

ETV Fault – Electronic Throttling Valve Circuit (Code 89)

Thermo King alarm code 89 indicates a failure in the Electronic Throttling Valve (ETV) control circuit. The ETV is a stepper-motor modulating valve in the suction line that regulates suction pressure and compressor loading on Thermo King SB-, SLXi, SLXe, SLX, SLX Whisper, T-Series, Precedent and TriPac reefer units. When the microprocessor cannot drive or read the ETV stepper coils correctly, it logs Code 89 and forces the unit into a protective mode — often unable to hold setpoint or pull down.

Check Electric Ready Input

Problem detected with the electric standby connection signal (Electric Ready).

Sensor Grades Not Set (Zone)

Zone sensor grades (calibration) have not been configured in the microprocessor.

Low Compressor Suction Pressure

Dangerously low compressor suction pressure detected.

Check Loader #1 Circuit

Fault in the compressor loader/unloader #1 circuit.

Check Loader #2 Circuit

Fault in the compressor loader/unloader #2 circuit.

Low Fuel Level

Tank fuel level is below the preset safety limit.

Failed Remote Return Air Sensor (CR)

Remote return air sensor failure preventing accurate zone temperature reading.

Check Fuel Level Sensor

The controller detects an invalid or inconsistent reading from the fuel level sensor.

High Compressor Pressure Ratio

Excessive pressure ratio detected between compressor suction and discharge, risking mechanical integrity.

Heater Fan Failure (CR)

Fault detected in the heater fan motor or circuit.

Controlling on Evap Coil Outlet Temp (CR)

Unit is controlling temperature based on evaporator outlet due to a primary sensor failure.

Low Evaporator Coil Temperature (CR)

Evaporator coil temperature is dangerously low, which may lead to icing or freezing.

Low Heater Fuel Level (CR)

Low fuel level detected specifically within the auxiliary heating system.

Check Remote Fan Speed (Zone)

The controller cannot detect or maintain the required speed for the remote zone fans.

Check Receiver Tank Press Sol Circuit

Electrical failure in the receiver tank pressure solenoid valve circuit.

Check Purge Valve Circuit

Failure in the purge valve circuit, compromising refrigeration cycle efficiency.

Check Condenser Inlet Sol Circuit

Error detected in the condenser inlet solenoid valve circuit.

Door Open Timeout (Zone)

The zone door has remained open longer than the allowed programmed setting.

Check High Discharge Pressure Sensor

Error in the high discharge pressure sensor (Replaced by code 86 in newer models).

Check Suction Line Sol Circuit (Zone)

Failure in the suction line solenoid valve circuit for a specific zone.

Unit Not Configured Correctly (Zone)

The unit configuration does not match the hardware or number of zones installed.

Check Remote Fans (Zone)

The remote zone fans are not operating as required.

Check Electric Heat Circuit (Zone)

Fault detected in the zone electric heating circuit.

Multiple Alarms - Can Not Run (Zone)

The zone has shut down due to the accumulation of multiple simultaneous critical alarms.

Check High Pressure Cut Out Switch

Fault in the High Pressure Cut Out (HPCO) switch or its circuit.

Check High Pressure Cut In Switch

Fault in the high pressure reset (cut-in) switch or its circuit.

Auto Switch from Diesel to Electric

The unit has automatically switched from diesel operation to electric motor operation.

Auto Switch from Electric to Diesel

The unit has automatically switched from electric motor to diesel operation.

Reserved for CR

Reserved for specific Cargo Register (CR) functions.

Check Alternator Excite Circuit

Fault detected in the alternator excitation circuit; the battery may not be charging.

Check PMW Liquid Injection Circuit

Failure in the Pulse Width Modulation (PMW) liquid injection circuit, crucial for compressor cooling.

Check Diesel/Electric Circuit

Error when attempting to switch between diesel and electric mode or vice versa.

Check Evap Coil Inlet Temp Sensor (CR)

Failure in the evaporator coil inlet temperature sensor (CR).

Check Evap Coil Outlet Temp Sensor (CR)

Failure in the evaporator coil outlet temperature sensor (CR).

Check Tank Level Sensor (CR)

Failure in the tank level sensor associated with the Cargo Logger or secondary unit.

Check Back Pressure Regulator (CR)

Indicates a problem with the suction pressure regulator or back pressure regulator, affecting temperature stability.

Setpoint Not Entered (Zone)

An active zone in the multi-temperature system has been detected without a defined setpoint.

Engine Run Time Maint Reminder #1/Service Due

Preventive maintenance reminder based on diesel engine operating hours.

Engine Run Time Maint Reminder #2

Second preventive maintenance reminder for the diesel engine.

Electric Run Time Maint Reminder #1

Maintenance reminder based on operating hours in electric mode (Standby).

Electric Run Time Maint Reminder #2

Second accumulated maintenance reminder for electric operation mode.

Total Unit Run Time Maint Reminder #1

General maintenance alert triggered after reaching a specific number of total unit operating hours.

Total Unit Run Time Maint Reminder #2

Second maintenance notification based on the total accumulated unit run time.

Controller Power On Hours

Reminder based on the total number of hours the controller has been powered on.

Check Spare Digital Inputs

Failure or unexpected reading in one of the configured auxiliary digital inputs.

Check Spare Digital Outputs

Problem in the circuit of an auxiliary digital output (relay or command).

Check Damper Motor Heater Output

Fault in the heater circuit for the defrost damper motor.

Log DAS Real Time Clock Battery Failure (DAS)

The Data Acquisition System (DAS) real-time clock battery has failed.

Abort Evacuation Mode

The evacuation (vacuum) mode has been aborted due to an error or manual intervention.

Not currently used

Error reserved for future functions or not currently defined.

Auto Switch Diesel to Electric Disabled

The unit was unable to perform the automatic switch from Diesel to Electric power.

Check Thermax Valve

Fault detected in the Thermax valve of the heating/defrost system.

Check Remote Drain Hose Heater Output (Zone)

Error in the remote drain hose heater output in a specific zone.

Lost CAN Communications to Expansion Module

Loss of communication between the main controller and the expansion module.

Lost Controller ON Feedback Signal

The controller is not receiving the feedback signal that the system is ON.

Software Version Mismatch

Software version incompatibility between the different modules of the unit.

Check Multi-Temp Fan Speed Control Output (Zone)

Error in the speed control of the multi-temperature evaporator fans.

Auto Switch Electric to Diesel Disabled

The unit was unable to perform the automatic switch from Electric to Diesel mode.

Alarm Not Identified

The system has detected an alarm condition that is not registered in its database.

Sensor Out of Range Low (DAS and HMI) (Zone)

A sensor (air, evaporator) is reporting a measurement below the minimum limit.

Sensor Out of Range High (DAS and HMI) (Zone)

A sensor is reporting a measurement above the maximum allowed limit.

DAS Failed Sensor (DAS)

Critical failure in a sensor dedicated exclusively to the Data Acquisition System (DAS).

Expansion Module Flash Load Failure

Error attempting to load or update firmware on the expansion module.

Low Suction Pressure Switch Failure

Inconsistent state or failure detected in the low suction pressure switch.

Lost CAN Communications to HMI

Communications lost between the main controller and the Human Machine Interface (HMI) display.

Check Suction/Liquid Heat Exchanger Bypass Valve

Indicates a problem with the operation of the suction/liquid heat exchanger bypass valve.

OptiSet Plus Profile Mismatch

Discrepancy detected between the OptiSet Plus configuration and the unit's operating parameters.

Primary Software Failed to Load

Unit main software failed to load correctly during startup.

Check Battery Condition

System has detected that the battery voltage is out of range or has low holding capacity.

Lost CAN Communications to Radio Expansion Board

Loss of communication over the CAN bus with the Radio Expansion Board (REB).

Log DAS Real Time Clock Invalid (DAS)

The Data Acquisition System (DAS) real-time clock is invalid or has reset.

Emission Control Failure

Dectected failure in the engine emission control system.

Low Engine Power Available

The unit detects that the engine does not have enough power to operate at full load.

Check Electronic Expansion Valve (CR)

Failure in the electronic expansion valve (EEV) circuit or mechanism.

Check Evaporator Pressure Sensor (CR)

The evaporator pressure sensor is sending signals that are out of range.

Check CO2 Tank Pressure Sensor (CR)

Failure in the sensor monitoring CO2 tank pressure in cryogenic systems.

Low CO2 Fuel Level (CR)

Low level of CO2 fuel detected in the storage tank.

TriPac Compressor Alarm

A generic alarm condition has been detected in the TriPac compressor system.

Log DAS Microprocessor Fault (DAS)

Internal failure detected in the Data Acquisition System (DAS) microprocessor.

Check Display Return Air Sensor (Zone)

The display return air temperature sensor is presenting erroneous readings.

Check Display Discharge Air Sensor (Zone)

The display discharge air temperature sensor is presenting erroneous readings.

Check DAS Digital Inputs (DAS)

Fault detected in the digital inputs of the Data Acquisition System (DAS).

REB Switching Off, Conservative to Full Null

The Radio Expansion Board powers off due to a system operational transition.

Check Relative Humidity Sensor Circuit

A problem has been detected in the relative humidity sensor circuit.

High Engine Coolant Temperature Check

The engine coolant has exceeded the safety temperature threshold.

DAS Clock Time Reset (DAS)

The Data Acquisition System (DAS) clock has reset to factory defaults.

Check Radio Expansion Board Configuration

The Radio Expansion Board configuration does not match the unit.

Check Auto Fresh Air Exchange Circuit

Fault detected in the automatic fresh air exchange system circuit.

REB On Back Up Battery, Alarms Disabled

The REB board is operating on its backup battery; telematics alarms may be limited.

Check Auxiliary Coolant Temp Sensor

Fault in the auxiliary coolant temperature sensor circuit.

Check Host Evaporator Blower Low Speed

Problem detected in the low speed of the main evaporator blower.

Check Host Evaporator Blower High Speed

Problem detected in the high-speed operation of the host evaporator blower.

Check Roadside Condenser Fan Motor Speed Circuit

Fault in the speed control circuit of the roadside condenser fan motor.

Check Curbside Condenser Fan Motor Speed Circuit

Fault in the speed control circuit of the curbside condenser fan motor.

Check Digital Scroll Output Circuit (Scroll Only)

A fault has been detected in the digital scroll compressor output control circuit.

Speed Request Communication Error

Communication error in the speed request between the unit controller and the engine ECU.

ECU Failed to Enable

The unit failed to enable or turn on the engine ECU following the logic sequence.

ECU Run Signal Failed

The controller sent the run signal but the ECU did not respond or confirm the running status.

Engine Wait to Start Time Delay Expired

The preset wait time for start-up preheating (glow plugs) has expired.

High Compressor Suction Pressure (Scroll Only)

Excessively high suction pressure detected in Scroll-type compressors.

Low Compressor Suction Ratio (Scroll Only)

Suction pressure ratio below safe operating limits for the Scroll compressor.

Low Compressor Discharge Pressure (Scroll Only)

Scroll compressor discharge pressure too low during operation.

Minimum ETV Discharge Superheat Temp (Scroll)

ETV controlled discharge superheat is at the minimum thermal limit.

I/O Controller to Application Controller Com Failure

Critical communication failure between I/O controller and application controller.

Generator Ground Fault

Current leakage to ground detected in the generator circuit.

Check Battery Charger Input Power

Problem detected with AC input power to the battery charger.

Check Battery Charger Output Power

Battery charger is not delivering expected output power for charging.

Battery Charger External/Environmental Fault

Battery charger failure caused by external or environmental factors.

Battery Temperature Sensor Alarm

Battery temperature sensor reports out of range readings or is disconnected.

Battery Charger Indicated Conditions

The battery charger has detected abnormal internal conditions requiring attention.

Generator Op Limit Vout to Frequency Ratio

Generator Voltage/Frequency ratio is outside functional limits.

Generator Frequency Range Fault

The generator output frequency is outside the allowed range (Hz).

Generator Operational Limit Output Current

The generator has reached or exceeded its operating output current limit.

Failed J1939 CAN Comm Base Controller/Charger

J1939 CAN communication failure between the base controller and the battery charger.

Check Fuel Pump Circuit

Electrical anomaly detected in the fuel pump circuit.