What causes the IMA light to come on?
The IMA light signals a fault in Honda’s Integrated Motor Assist hybrid system. It is most commonly tied to the high-voltage battery, its cooling or the motor generator, though electrical sensors and control software can also trigger it. If the light appears, treat it as a warning and have the vehicle scanned by a qualified technician as soon as possible.
What the IMA light indicates
The IMA light is part of Honda’s hybrid system status indicators. In most models, a solid amber IMA light means there is a fault that may reduce hybrid performance or battery charging. A flashing light can indicate a more urgent fault or a temporary fault that requires attention after a shutdown. The exact meaning can vary by model year and the vehicle’s other warning indicators. A diagnostic scan is required to read the fault codes from the Hybrid Battery Management System (BMS) and ECU.
Common causes of the IMA light coming on
Possible reasons fall into several categories, from the battery itself to sensors and cooling systems. The list below highlights the most frequent culprits reported by technicians and published guides:
- Worn or failing high-voltage battery pack: diminished capacity, cell faults, or weak modules can trigger the IMA warning.
- Battery cooling system problems: a clogged or failing cooling fan, low coolant level, or restricted airflow can cause overheating and trigger the light.
- Malfunctioning motor-generator units (MG1/MG2): issues with the electric machine can set fault codes and illuminate the IMA light.
- Sensor or wiring faults in the IMA subsystem: loose connections, corroded contacts, or damaged wiring can produce erroneous readings.
- Battery management system (BMS) faults or improper state of charge: software or hardware faults within the BMS can trigger alarms and disable power assist.
- ECU/software issues: outdated or corrupted hybrid control software may throw codes or fail to properly manage charging/discharging.
- Electrical faults or parasitic drains in the hybrid system: abnormal current draw or charging conflicts can trigger warnings.
These are general patterns observed across many Honda hybrids; exact causes depend on the model and year, so diagnostic data is essential.
What to do if the IMA light comes on
Taking prompt, careful steps can prevent further damage and help protect the hybrid system.
- Check for other warning lights and note symptoms such as loss of power, unusual noises, or unequal acceleration.
- Drive conservatively and avoid high speeds or heavy acceleration. If the light is flashing or the vehicle enters reduced-power mode, stop driving as soon as it is safe.
- Inspect the IMA cooling system awareness: ensure the cooling fan runs when the car is under load and that there are no obvious signs of coolant leaks or low levels, if it can be checked safely.
- Have the vehicle scanned with a Honda-specific hybrid diagnostic tool (or at a Honda dealer) to read IMA/BMS/ECU codes. OBD-II scanners may not read hybrid codes reliably.
- Follow the repair facility’s guidance based on the codes; common fixes include battery pack service, BMS calibration, motor-generator replacement, or software updates.
Timely diagnosis can prevent further damage and preserve battery life; continuing to drive with a confirmed fault risks reduced efficiency or possible battery failure.
Maintenance and prevention for IMA system health
Regular care helps reduce false alarms and extend system life. Key practices include:
- Scheduled inspections of the hybrid system, including high-voltage battery checks and cooling system service.
- Maintaining proper coolant levels and following Honda’s service intervals for coolant replacement.
- Ensuring the cooling fan operates correctly and that airflow around battery and inverter components remains unobstructed.
- Using manufacturer-recommended charging practices and avoiding deep discharges that stress the battery.
- Keeping software and control modules up to date with recalls or service campaigns where applicable.
Proactive maintenance helps catch developing issues before they trigger the IMA warning and can help sustain hybrid performance.
Summary
The IMA light is a warning about the health of Honda’s integrated hybrid system. It most often points to battery health, cooling, or control electronics. If it comes on, obtain a diagnostic assessment to identify the specific fault code and follow professional repair guidance. With timely service, most IMA-related issues can be resolved without compromising safety or long-term reliability.
