Thermo King Alarm & Fault Codes: 63, 10, 20, 26, 61, 32, 25

Food, medicine, and electronic components are only some of the several things that are temperature-sensitive when transported, whether through air, land, or sea.

Thermo King is leading the way to transport temperature control since 1938. From vans, trucks, and trailers to boats and airplanes, Thermo King has a temperature control system that can address all your needs. With this guide you will be able to troubleshoot your Thermo King unit.

How does Thermo King work?

Thermo King works by using liquid carbon dioxide as a coolant. Liquid carbon dioxide alone won’t produce cold air as it needs to undergo a process to make use of it.

Cooling is not needed all the time since the user sets the temperature. As a result, the liquid carbon dioxide has to be stored securely. A refillable tank mounted under the vehicle chassis is used to store liquid carbon dioxide. When the microprocessor controller demands cooling, the liquid carbon dioxide is then allowed to flow from the tank to the evaporator coils.

The coils alone won’t cool the cargo space. Remember the liquid carbon dioxide that is in the evaporator coils? As air pushed by electric fans pass through the coils, the liquid carbon dioxide evaporates, cooling the air that passes over it.

The product of this entire process is cold air, which circulates through the whole cargo space, maintaining the temperature set by the user.

What engine does Thermo King use?

The engine used by Thermo King is specific to its applications. It focuses on high-efficiency, which means high performance without sacrificing emission levels. Before the engine makes it to a Thermo King product, it goes through a rigorous testing and validation process to ensure compliance with standards.

Thermo King uses the GreenTech engine, which is known to have the lowest emissions and highest performance. Unlike its competitor brands, the GreenTech engine puts reduced emissions and pollution without sacrificing overall performance a top priority. Because of its commitment to the environment, the GreenTech engine exceeds all environmental requirements. Since we’re talking about saving the environment and reducing emissions, let’s plant seeds and grow flowers. You might also be interested in growing Sansevieria plants.

It is quite common for high-performance engines to have high emissions. That is not the case for GreenTech engines. Its engines are high-performance without sacrificing its commitment to the environment. GreenTech engines have the cleanest engines on the refrigeration market. It is also compatible with B5 fuels, placing it another step forward to being environmental-friendly. While we’re on the topic of fuel, we have an article about fuel transfer tanks you might be interested in.

How do I clear and reset the Thermo King alarm code?

Before we move forward to the specifics of each Thermo King alarm code, let us first discuss how to clear and reset a Thermo King alarm code.

A Red diamond warning indicates an alarm code, which may occur for many reasons. Don’t panic because it’s easy to clear and reset a Thermo King alarm code!

  1. Press the check button and the on button at the same time.
  2. Release the check button and the on button, then press the equal sign button.
  3. Wait for a few seconds.
  4. The red diamond warning should be gone by this time, which indicates the unit has reset.

Thermo King Alarm Codes

Here’s a list of frequent Thermo King alarm codes or APU fault codes that may get you into trouble. Do note that error codes with parenthesis may exist at the same time as alarm code 84. It may also clear out automatically.  

Codes we’ll cover      
63 17 61 89
10 26 25 13
37 35 66 44
84 23 18  

Code 63

Code 63 has a red status, which needs immediate action. This error code indicates that the engine or vapor motor stopped working. It’s sometimes called vapor lock too.

A common cause of vapor lock is heat. When there is too much heat in the exhaust system, engine, or ambient temperature, fuel may vaporize in the lines, causing the vapor motor to stop working.

The most effective way to address this issue is to let the engine cool down. Look for a shade and park your vehicle. Allow the engine to rest for a few minutes. If it’s possible, pour cold water over the fuel pump and fuel lines. Be sure the engine has cooled before doing this. While on the topic of machines and engines, you might be interested in plasma cutters and mini metal lathes.

Code 17

Code 17 has a yellow status, which needs checking as specified. This error code indicates the engine failed to crank when the microprocessor requested a start. It is a frequent error code experienced by drivers, technicians, and operators.

Check the battery, cables, and starter. In most cases, troubleshooting these components can lead to knowing the problem and fixing code 17. 

Check the battery if it is receiving the proper amount of voltage. Load testing the battery checks if it can hold the right amount of charge. Next, check the relay interface circuit board, which controls the fuel shut off solenoid. When checking this, be sure to wear a wrist ground strap to avoid internal damage to the circuit board. Once you’ve checked the battery and the relay interface circuit board, it’s time to check for broken wires and if the pin connectors are attached appropriately. Take note of any broken wires and reattach loosely attached connectors.

Code 26

Code 26 has a yellow status, which needs checking as specified. This error code indicates to check the refrigeration capacity of your Thermo King. The refrigeration capacity measures how effective the cooling capacity of your Thermo King.

While in use, manually monitor the temperature. A consistent drop in temperature could indicate that your Thermo King is low in freon, or it’s losing freon. If possible, monitor the temperature in equal time intervals and check the results at the end of the day. Doing so will make it easier for you to spot the temperature levels at different times.

If the alarm code doesn’t go away, report the alarm to Thermo King at the end of the day. Present the data you gathered to make it easier and faster to spot the problem.

Code 37

Code 37 has a green status, which indicates that it is OK to run your Thermo King. When you encounter Code 37, start by checking the engine coolant level. If it is within normal levels, check the sensor.

Residues stuck inside the reservoir cause inaccurate engine coolant level readings. Carefully pull out the sensor and wipe it with a clean cloth. If the error is still there, check pins 14 and 37 at the microprocessor and make sure all the pins are correctly attached.

If you just repaired a leak from your Thermo King, you need to refill the coolant. After doing so, press the TK button, then press and hold the equal sign button.

Code 10

Code 10 has a red status, which requires immediate action. This error code indicates high discharge pressure, which makes troubleshooting difficult. 

The first option you can do is to check if there are any broken fan belts. Check for faulty or missing belts by opening the upper and lower front doors. If necessary, replace the belt that has worn out. While you are at it, check for loose bearings. 

The second option you can do is to check if the 12-volt battery is defective. A typical sign of a worn-out battery is if the unit loses power even before you engage the starter. Using a voltmeter, jump the starter and check if the battery voltage is 12V. If unsuccessful and the voltmeter reading is 0V or 1V, it is an indication of a bad battery. The only way to fix this is to replace the bad battery with a new one.

The third option you can do is to check if the high-pressure cutout switch is working correctly. You can find the HPCO on top of the compressor. If you bypassed the HPCO and the unit starts, it means the HPCO switch is defective.

Code 61

Code 61 has a yellow status, which needs checking as specified. This error code indicates there is a low battery voltage in your Thermo King reefer.

The design of the in-cab controller lets the voltage go through the on/off switches before the in-cab controller. In most cases, corroded switches cause a drop in battery voltage, which results in low battery voltage. You can find the on/off switches on the nearside of the fridge unit.

Code 25

Code 25 has a yellow status, which needs checking as specified. This code indicates the alternator needs checking. The alternator is a device that converts electrical energy from mechanical energy by alternating current.

Start by going through the small things, such as checking the tightness of the connections, checking the amps it is pulling, and checking the battery. After going through the wires and connections, clear the error code and run in continuous mode. Did the error code disappear? If the troubleshooting steps you took did not fix the issue, this could be an indication of a faulty alternator. A great option is to replace the alternator with a new one. If you just had it replaced, either you got a defective alternator, or your battery has a bad cell.

Code 35

Code 35 has a red status, which indicates immediate action is needed. The unit will not be able to operate and should remain shut down.

This error code indicates a problem with the run relay circuit. The first possible fix for this issue is a software update. A quick software update to your unit may fix the code 35 error. If it does not, check the alternator is properly working, the battery is in good health, and the connections are securely in place.

Code 66

Code 66 has a red status, which indicates immediate action is needed. The unit immediately needs repair if it is off.

This error code indicates your Thermo King has a low engine oil level. To fix this issue, you need to refill your engine with oil. In case you recently filled your engine with oil, check the oil level sensor. Speaking of oil, you might want to read on how to reuse waste oil instead of discarding it right away.

The oil level sensor is on the passenger side. To access, open the side door and look for the oil pan. You can find the oil level sensor by looking for the oil pressure switch. It has one wire going to it and two wires on the plastic piece on top of the oil pan.

If the problem is still there, this could be an indication of a defective oil level sensor. Before deciding to replace the oil level sensor, disconnect and clean the sensor first.

Code 84

Code 84 has a green status, which indicates you can report the alarm at the end of the day. This error code usually happens as a result of other alarms in your Thermo King. It is a temporary condition and should go away by itself.

Your Thermo King unit should shut down for about 15 minutes. After 15 minutes, your Thermo King should restart. If it does not, then you might have to wait for the condition to reset. In most cases, the other error codes that came with this error code should also clear.

If it does not seem to work, repeat two more times. If the error persists on the third attempt, the error code that caused your Thermo King to turn off will appear on your control panel. The unit will then automatically shut down. Once you fix code 84, the error should automatically clear after a restart.

Code 23

Code 23 has a red status, which means immediate action is required. This error code indicates a faulty cooling cycle.

The code 23 error is an indication that your Thermo King is low on freon, has run out of freon, the compressor is defective, or there is discharge pressure.

Start by making sure all your belts are in place. If they are secured, check the freon. The freon needs replacing if it is low level or it has run out. The freon is in the lower front cover of your Thermo King’s APU AC system. The ports you are looking for are the ones coming from the a/c compressor. Your Thermo King’s engine should be running in a/c mode while doing this procedure.

Code 18

Code 18 has a yellow status, which means it needs checking as specified. If the unit is running, you can check on the alarm at the end of the day, then report it. If your Thermo King is off, the best action is to repair it immediately.

This error indicates that the engine has a high coolant temperature, which could cause the engine to overheat in a shorter period than usual. A code 18 error is a little tricky to troubleshoot as it may involve several factors such as a low coolant level or a leak.

Start by checking your Thermo King’s thermostat. It may be defective or covered with dirt. Clean it off and check if the same error code is appearing. Next is to check if the water pump is working correctly.

If you’ve checked the thermostat and water pump and have determined they are working correctly, you may want to pressure wash the radiator. A dirty radiator may hinder the circulation of air, which may cause overheating.

If the above steps did not work, try checking if the engine oil is within the usual level. While you are at it, check if the oil is in its normal consistency. The diesel can mix with the engine oil if there is leaking.

Code 50

Code 50 has a green status, which means it’s good to continue using your Thermo King. It has something to do with resetting the time of your unit.

This error code usually comes up whenever the main power gets disconnected from the microcontroller. To address this issue, turn on the unit and wait for the setpoint temperature and box temperature to appear. Once it appears, press and hold the TK button until you see “Pre-Trip” on your control panel screen. Then, press and hold the cycle button until you see the time/date. Continue through the following screens and make sure to press the equals button.

Once you have completed the above steps, the error code should go away. Note that the above steps are for alarm checking and will not affect the reefer on how it operates.

Code 32

Code 32 has a red status, which indicates immediate action is necessary. This error code appears if the refrigeration capacity is low. The refrigeration capacity is a measure of the cooling capacity effectiveness of your Thermo King.

If your unit is running, immediately turn it off. A compressor that is running in low freon may cause it to burn out. You will need to add freon into the unit. Be sure you use a set of gauges to monitor that you are getting proper pressures. Before restarting the unit, check for leaks.

Code 20

Code 20 has a yellow status, which means it needs checking as specified. This error code indicates the vapor motor failed to start. Code 20 is a common alarm code that you might encounter with Thermo King products.

There is likely a problem with your fuel system, which is causing the vapor motor to fail. A problem with the fuel system involves several factors.

To check for solenoid failure, switch on the unit while keeping a finger or two on the solenoid. If the unit buzzes, that indicates a startup. The solenoid should clunk before the starter engages. If you hear a clunk, it means the solenoid has energized, and it is working as expected. 

For a clogged fuel system, check the inline fuel filter by removing the bolt and washer. Remove the filter and clean it well. Reinstall the bolt and washer you removed.

For air in a fuel system, start by loosening the hand primer found on the transfer pump. Check if the fuel tank is at least ¾ full. Otherwise, add fuel to the tank. Next, look for the bleeder bolt located on top of the injection pump. Let air inside the fuel system out by opening it. If the unit doesn’t turn on, continue to pressurize the tank.

Code 89

Code 89 has a green status, which indicates it is good to run. If you see this error code, you need to check the electronic throttling valve circuit.

The electronic throttling valve (ETV) circuit extends maintenance intervals, reduces fuel cost, and improves temperature control on Thermo King products.

The ETV circuit is on the top middle of the compressor. Check for loose plugs and clean the ground wires as these are the usual causes of code 89.

Code 13

Code 13 has a yellow status, which indicates it needs checking as specified. The sensors on your Thermo King need checking as one or more sensor is not working as expected.

To check if the sensors are working, you need to monitor the temperature manually. The sensors that need checking are the discharge air temperature sensor, return air temperature sensor and coil temperature sensor. Thirty minutes after a defrost is complete, the sensors should read within 30 °F of each other. You will have to observe and compare all three sensors to determine which sensor is faulty.

Once you have determined the sensor at fault, you can apply lube to the micro connection found on the back of the microprocessor. If it does not work, you will have to replace the sensor with a new one.

Code 44

Code 44 has a red status, which requires immediate action. This error code tells you to check the fuel system.

In most cases, this error code indicates that your Thermo King lacks fuel. Aside from adding fuel, look for the banjo fitting on the transfer pump line. Unscrew the screen and clean it. Also, check if you are getting fuel from the transfer tanks.

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