Note: P0125 is "Insufficient Coolant Temperature for Closed Loop Fuel Control," not a throttle position code. If your 2022 Cadillac XT5 is showing P0125, the engine isn't warming up to operating temperature, affecting fuel system operation.
What P0125 Actually Means
P0125 indicates the engine coolant temperature hasn't reached the threshold required for the fuel system to enter closed-loop operation within a reasonable time. Closed-loop mode uses oxygen sensor feedback to fine-tune fuel delivery—this requires a warmed engine. P0125 suggests a cooling system problem preventing normal warm-up.
Why Coolant Temperature Matters
During cold operation, the ECU uses pre-programmed fuel maps (open loop). Once the engine warms up, it switches to closed-loop mode, using O2 sensor feedback for precise fuel control. If the engine never warms up, it stays in enriched cold mode, wasting fuel and increasing emissions.
Common Causes of P0125
A stuck-open thermostat is the most common cause. The thermostat should remain closed until the engine warms up, but if it's stuck open, coolant circulates continuously through the radiator, preventing the engine from reaching operating temperature.
A missing or incorrect thermostat can cause this issue. Some owners remove the thermostat (thinking it prevents overheating), but this prevents proper warm-up.
A failed coolant temperature sensor can report incorrect temperatures, though this more commonly triggers sensor-specific codes rather than P0125.
Diagnostic Approach
Monitor coolant temperature during warm-up. It should rise steadily to 195-220°F within 10-15 minutes of driving. If it stays low or rises very slowly, the thermostat is likely stuck open. Feel the upper radiator hose—it should be cool until the thermostat opens, then become hot.