CAT 61 Fault Code: Very High Coolant Temperature
Also called High Coolant Temperature Warning, High/Very High Coolant Temperature
Very High Coolant Temperature · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 61 (SPN 110 / FMI 16) means the ECM has detected that engine coolant temperature has climbed above a critical threshold for a sustained period after the engine has been running for at least 30 seconds. This is an overheating event, not an electronic sensor fault, and it calls for immediate attention to avoid engine damage.
Critical severity. This code flags an actual overheating condition, not a wiring glitch. Caterpillar notes it can represent a critical event depending on the engine family and how long the high temperature persists. Continued operation risks head gasket failure, warped heads, or worse.
What does CAT error code 61 mean?
CAT fault 61 corresponds to SPN 110 / FMI 16 and covers a family of coolant and intake air overtemperature conditions across C7, C9, C-10, C-12, C11, C13, C15, C18, and 3406E engines. The exact trigger temperature and time window vary by engine and vehicle type, but in every version the ECM has confirmed the engine has been running for at least 30 seconds and coolant (or in one variant, intake manifold air) temperature has stayed above a set threshold longer than a short confirmation window.
Caterpillar is explicit that most versions of this code represent a real thermal event in the cooling system itself, not a failure of the sensor or wiring circuit. That means the first assumption should be that the engine actually got too hot, not that a sensor is lying, though a faulty sensor or connector is still on the causes list and should be checked once obvious mechanical causes are ruled out.
One listed variant ties the code to high intake manifold air temperature (above 110 °C (230.0 °F) for more than two seconds) combined with coolant temperature above 99 °C (210.0 °F), showing that on some engines this code can also reflect a charge air cooling problem rather than pure coolant overheating.
What triggers a CAT 61 code?
Depending on engine and vehicle configuration, the ECM sets this code when: coolant temperature is at least 111 °C (232 °F) for more than four seconds (C7 non-emergency); at least 116 °C (241 °F) for more than four seconds (C7 emergency / C9); at least 121 °C (250 °F) for more than four seconds (C9 emergency with automatic transmission); at least 108 °C (226 °F) for more than ten seconds (C7 non-emergency, lower-severity variant); at least 113 °C (235 °F) for more than ten seconds (C7 emergency / C9, lower-severity variant); at least 118 °C (244 °F) for more than ten seconds (C9 emergency automatic, lower-severity variant); greater than 106 °C (223 °F) (C-10 or C-12); greater than 111 °C (232 °F) (3406E); or greater than 110 °C (230 °F) for more than 20 seconds on other covered engines. A separate intake-air-temperature variant sets when intake manifold air temperature exceeds 110 °C (230.0 °F) for more than two seconds while coolant temperature is above 99 °C (210.0 °F). In all cases the engine must have been running at least 30 seconds before the code can set.
Common causes of 61
- High ambient air temperature or high inlet air temperature
- Low coolant level
- Radiator failure or a restriction in the cooling system
- Faulty water temperature regulator (thermostat)
- Faulty coolant temperature sensor or its circuit/harness
- Excessive engine load, including running the engine in a lug condition
- Improper antifreeze, wrong mix or wrong type
- Air trapped in the cooling system
- Fan clutch failure or malfunction
- Radiator filler cap failure
- Charge air cooler failure
- Fan, fan belt, or fan shroud failure
- Restriction in the air inlet or exhaust system
- Water pump failure
- High outside temperature or high altitude operation
How to troubleshoot CAT 61: first checks
- Stop and let the engine idle or cool per your machine's procedure before shutting down; do not shut off a severely overheated engine abruptly if avoidable, since that can trap heat in the block and heads
- Once safely cooled, check coolant level in the recovery tank and radiator, and inspect for external leaks at hoses, the radiator, and the water pump
- Inspect the radiator for debris, bent fins, or internal restriction, and check the radiator filler cap for a weak or failing seal
- Check the fan, fan clutch, fan belt, and fan shroud for damage, slippage, or failure to engage
- Verify coolant mix and type match the manufacturer's specification, and bleed air from the system if air has been introduced (e.g., after a coolant service)
- Inspect the coolant temperature sensor and its wiring/connector for corrosion or damage once mechanical causes are ruled out
- Check for restrictions in the air inlet or exhaust system and inspect the charge air cooler for damage or blockage
- Review recent duty cycle for excessive load or lugging conditions, and consider high ambient temperature or high-altitude operation as contributing factors
How the code clears
No separate reset procedure is listed for this code. Because it reflects an actual thermal event rather than a latent electronic fault, the code should clear on its own once the underlying overheating cause is found and corrected and coolant temperature returns to a normal operating range. Confirm the repair by monitoring coolant temperature through a full duty cycle before returning the machine to normal service.
Affected models and serial ranges
61 appears in our records across 4 CAT models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C11 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 61 mean?
It means the ECM detected that engine coolant temperature (or in one variant, intake manifold air temperature) exceeded a critical threshold for longer than a brief confirmation window after the engine had been running at least 30 seconds. It is a real overheating event, not a wiring or sensor fault by itself.
Can I keep operating with code 61 active?
No. Caterpillar describes this as a critical or event-level code tied to actual overheating. Continuing to run the engine risks head gasket failure, warped cylinder heads, or other serious internal damage. Stop as soon as it is safe to do so.
What is the most common cause of code 61?
Low coolant level, a failing radiator or cooling system restriction, and a faulty water temperature regulator (thermostat) are among the most frequently cited causes, along with excessive engine load or lugging.
Is code 61 always caused by a bad sensor?
No. Caterpillar specifically notes that most versions of this code represent an actual thermal event in the cooling system, not an electronic system fault. A faulty coolant temperature sensor or its circuit is on the list of probable causes, but it should be checked after ruling out mechanical and cooling system problems.
Does code 61 apply to intake air temperature too?
Yes, one documented variant sets when intake manifold air temperature exceeds 110 °C (230.0 °F) for more than two seconds while coolant temperature is also above 99 °C (210.0 °F). In that case, causes like charge air cooler failure and air inlet restrictions become especially relevant.
Will code 61 clear itself after I fix the problem?
No separate reset procedure is documented. Since the code reflects a real temperature event, it should clear once the root cause is corrected and coolant temperature returns to normal, but always verify by monitoring temperature during a follow-up run.
Does the temperature threshold differ by engine model?
Yes. Thresholds and timing vary significantly by engine family and vehicle type, ranging from as low as 106 °C (223 °F) on C-10/C-12 engines up to 121 °C (250 °F) on certain C9 emergency vehicle configurations with automatic transmissions.