CAT Engine 168 Fault Code: High Engine Coolant Temperature - Derate
High Engine Coolant Temperature - Derate · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 168, SPN 110 FMI 16, means the ECM has detected a moderately high engine coolant temperature after the engine has run past a set time and reached a trip point. The engine will derate power if the customer parameter for derate is enabled and the warning lamp will come on.
High severity. This is a derate condition, not an immediate shutdown, but continuing to run the engine hot risks further damage and the machine will lose power on its own. Stop and address the cooling issue as soon as it is safe to do so.
What does CAT Engine error code 168 mean?
This code fires when the ECM sees engine coolant temperature climb to a trip point that it treats as an event, separate from the raw voltage-fault codes for the coolant temperature sensor itself. It is a real thermal condition, not a wiring glitch, as long as the sensor circuit codes are not also active.
When the ECM confirms the condition, it logs the event, lights the warning lamp if the machine has one, and begins reducing available engine power at a rate of one percent per second. This derate is a protective measure meant to reduce heat generation and buy the engine some margin before real damage occurs.
The derate only happens if the machine's 'Enable Derate' customer parameter has been turned on. If that parameter is disabled, the ECM will still log the code and light the lamp, but it will not cut power.
What triggers a CAT Engine 168 code?
The ECM sets this code when all of the following are true: the engine has been running for more than 185 seconds, the coolant temperature has reached the programmed trip point for this event, and none of these related codes are currently active: 0110-03 (Engine Coolant Temperature voltage above normal), 0110-04 (Engine Coolant Temperature voltage below normal), and 0168-01 (Electrical System voltage low).
Common causes of 168
- Actual high engine coolant temperature from a cooling system problem such as low coolant level, a failing thermostat, a clogged radiator, a bad fan clutch or fan drive, or a slipping/damaged fan belt.
- Coolant flow restrictions from a collapsed hose, scaled radiator, or blocked water jacket that keep heat from being carried away fast enough.
- Environmental or duty-cycle causes such as heavy load, high ambient temperature, or restricted airflow to the radiator (blocked fins, debris, shrouding issues) pushing coolant temperature past the trip point.
- A genuinely hot engine condition that has nothing to do with the coolant temperature sensor circuit itself, since the code will not set if the sensor voltage-high or voltage-low codes are already active, or if the electrical system voltage is low.
How to troubleshoot CAT Engine 168: first checks
- Check coolant level and look for leaks at hoses, the radiator, water pump, and heater core connections.
- Inspect the radiator core and fins for mud, debris, or bent fins blocking airflow, and clean if needed.
- Verify the fan clutch, fan drive, and belt are functioning and not slipping or damaged.
- Confirm the thermostat is opening properly and not stuck closed.
- Check for any active diagnostic codes for the coolant temperature sensor circuit (0110-03 or 0110-04) or for electrical system low voltage (0168-01), since any of these being active will change how this code behaves.
- Look at recent duty cycle: was the machine under heavy load or in high ambient heat when the derate occurred, which can point to a load or airflow issue rather than a component failure.
How the code clears
No separate clearing procedure is listed for this code. Once the actual coolant temperature drops back below the trip point and stays there, the derate should back off since it is tied directly to the live coolant temperature reading. Confirming the repair with a scan tool and a normal operating cycle is good practice, but no distinct reset step is described.
Frequently asked questions
What does CAT code 168 SPN 110 FMI 16 mean?
It means the engine's ECM has detected engine coolant temperature at or above a programmed trip point after the engine has run more than 185 seconds, and the ECM is treating it as a high coolant temperature event that can trigger a power derate.
Will my CAT engine shut down when this code is active?
No shutdown is described for this code. Instead, if the 'Enable Derate' parameter is turned on, the ECM reduces engine power gradually at one percent per second rather than cutting the engine off.
Can I keep working with this code active?
You can technically keep running, but the engine will progressively lose power if derate is enabled, and continuing to operate a hot engine risks further damage. It is best to stop and diagnose the cooling system as soon as it is practical.
Why would this code not set even though my coolant is hot?
This code will not become active if either of the coolant temperature sensor voltage fault codes (0110-03 or 0110-04) or the electrical system low voltage code (0168-01) is already active. Those conditions get diagnosed and cleared first.
Is this a sensor problem or an actual overheating problem?
As long as the sensor circuit codes (0110-03 and 0110-04) are not active, this code reflects an actual coolant temperature reading at or above the trip point, meaning it should be treated as a real cooling system issue, not just a sensor glitch.
Does every CAT machine derate when this code sets?
Only machines where the 'Enable Derate' customer programmable parameter has been enabled will see the power reduction. Others will log the code and light the warning lamp without a power cut.
What should I check first if I get this code?
Start with coolant level, radiator cleanliness, fan clutch and belt condition, and thermostat operation, since these are the most common physical causes of a genuine high coolant temperature event.