Symptoms
- Gas engine stays on even when stopped or at low speed
- Engine runs continuously instead of cycling on and off as expected
- No warning lights accompany the behavior
- Happens more in extreme temperatures or with a low hybrid battery
Likely causes
- CommonHybrid battery charge too lowThe engine will run to recharge the hybrid battery when its charge drops below a certain threshold.
- CommonCabin climate control demandExtreme heat or cold can require the engine to run for heating or to power the AC compressor efficiently.
- PossibleEngine or cabin still warming upMany hybrids keep the engine running until it reaches operating temperature, especially in cold weather.
- PossibleEmissions system regeneration cycleOccasional engine-run cycles are needed to maintain emissions components.
What to do
- Check the hybrid battery charge level on the dashboard; a low level explains extended engine running to recharge it.
- Note the outdoor temperature and whether heating or AC is in heavy use, since this commonly keeps the engine running.
- Allow the car to fully warm up on a cold start before expecting electric-only operation.
- If the engine runs continuously even with a full hybrid battery and mild weather, that's less typical and worth noting.
- Check for any dashboard warning lights that might explain forced engine operation.
- Compare against how the car has behaved in the past under similar conditions to judge if this is a change.
When to call a pro
If the engine runs constantly despite a full battery, mild weather, and no clear cause, have a dealer scan the hybrid system.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.