P0125 on Subaru vehicles
Coolant Too Cold for Closed-Loop Fuel Control — what it means on a Subaru, whether it's safe to drive, and the fixes by model and year.
P0125 on a Subaru means coolant too cold for closed-loop fuel control. Most vehicles stay drivable short-term, but diagnose it promptly. The most common cause is thermostat stuck open or partially open (typically $80–$350). Pick your Subaru model below for its known failure patterns, recalls, and TSBs.
What does P0125 mean on a Subaru?
P0125 is set when the engine fails to reach the calibrated closed-loop threshold temperature within a calibrated time and distance. Closed loop fuel control requires the engine to be warm enough that the oxygen sensors are reliable and the ECM can trust their feedback. When coolant never crosses that threshold, the ECM remains in open loop indefinitely and sets P0125 as evidence the engine is not reaching its operating temperature.
P0125 is a standardized OBD-II code, so its definition is the same on every Subaru. What differs by model and engine is which cause is most likely — pick your Subaru model below for a diagnosis tuned to its known failure patterns, recalls, and TSBs.
Is it safe to drive a Subaru with P0125?
In most cases a Subaru stays drivable for short trips with P0125 active, but diagnose and repair it promptly. This is a low-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on the model and engine.
What causes P0125 on a Subaru?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Thermostat stuck open or partially open | Most common | $80–$350 |
| Wrong-temperature thermostat installed | Common | $30–$200 |
| Failed engine coolant temperature (ECT) sensor reading low | Occasional | $80–$250 |
| Cooling fan running continuously due to a separate fault | Occasional | $100–$500 |
| Heater core bypass leak letting coolant circulate freely | Rare | $50–$250 |
Repair costs are typical US ranges and vary by Subaru model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.
P0125 by Subaru model
Select your Subaru model and year for a P0125 diagnosis tuned to that vehicle's failure patterns, recalls, and TSBs.
Subaru Outback
1,651 NHTSA owner complaints · 24 recalls on record across the years covered below.
Subaru Forester
765 NHTSA owner complaints · 17 recalls on record across the years covered below.
Complaint and recall counts are NHTSA totals for the model years covered on this site, not counts specific to P0125.
P0125 on other makes
Other codes on Subaru vehicles
P0125 on a Subaru: frequently asked questions
What does diagnostic trouble code P0125 mean on a Subaru?
P0125 is set when the engine fails to reach the calibrated closed-loop threshold temperature within a calibrated time and distance. Closed loop fuel control requires the engine to be warm enough that the oxygen sensors are reliable and the ECM can trust their feedback. When coolant never crosses that threshold, the ECM remains in open loop indefinitely and sets P0125 as evidence the engine is not reaching its operating temperature. P0125 is a standardized OBD-II code, so the definition is the same on every Subaru — which cause is most likely varies by model and engine.
What are the symptoms of P0125 on a Subaru?
Check Engine Light is illuminated. Heater output weak or slow to warm up. Temperature gauge sits below normal. Reduced fuel economy. Rough idle when cold (engine stays in cold-start enrichment longer than expected). Cold-start drive cycle takes much longer to complete emissions monitors
What causes P0125 on a Subaru?
Thermostat stuck open or partially open (most-common). Wrong-temperature thermostat installed (common). Failed engine coolant temperature (ECT) sensor reading low (occasional). Cooling fan running continuously due to a separate fault (occasional). Heater core bypass leak letting coolant circulate freely (rare)
Is it safe to drive a Subaru with P0125?
In most cases a Subaru stays drivable for short trips with P0125 active, but it should be diagnosed and repaired promptly — this is a low-severity code. Ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on the model and engine.