Honda Shuttle: 12V auxiliary battery drain causing IMA fault

The GP2 Fit Shuttle Hybrid uses Honda's first-generation IMA (Integrated Motor Assist) system, which requires a separate 12V lead-acid auxiliary battery to power the hybrid control module, body control module, and ancillary electronics. Unlike full hybrid architectures, the IMA system does not robustly top-charge the 12V battery from the main NiMH high-voltage pack under all operating conditions. Frequent short trips and extended city driving leave the 12V battery in a chronic partial-discharge state. When the auxiliary battery drops below the voltage threshold required to initialise the IMA control module, the system triggers an IMA fault and disables hybrid motor assist, reverting to petrol-only operation. The 12V battery is commonly overlooked during standard hybrid servicing.

• IMA warning light illuminated on instrument cluster
• Loss of electric motor assist — petrol engine only operation
• Difficulty starting or vehicle fails to start
• Multiple warning lights appearing simultaneously across systems
• Fault codes that clear temporarily but return within days

1. 1

   Check battery manufacture date on the label; replacement every 3–4 years is recommended in NZ conditions.

2. 2

   Inspect the IMA battery cooling fan inlet located behind the rear seat for blockage with debris.

3. 3

   If a workshop inspection is possible: Load-test the 12V auxiliary battery with a dedicated battery conductance tester — a simple multimeter voltage check is insufficient to detect capacity loss.

Parts involved: 12V battery.

$280 to $750 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “When was the 12V auxiliary battery last replaced and what brand was fitted?”
• “Has the IMA warning light ever appeared during ownership?”
• “Has the vehicle had any no-start events or recurring warning lights?”
• “Has the hybrid system been serviced by a Honda dealer recently?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.