The Problem
2024 Hyundai IONIQ 6 SE Long Range RWD (11,200 miles) brought in after intermittent power reduction during highway driving following a scheduled coolant service at a non-EV shop. 'Performance Limited — Motor Temperature High' shown on cluster. P0C46 confirmed via GDS2.
Diagnostic Procedure
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1. Confirm P0C46 front motor. Coolant reservoir full. No external leaks. P0C46 appears only after 15+ minutes of sustained highway speed.
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2. Monitor front motor coolant temperature during highway simulation load test. Front motor coolant inlet: 33°C. Front motor coolant outlet: 79°C — 46°C delta. Rear motor: 16°C delta under same conditions. Front motor not getting adequate coolant flow.
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3. Check for air in cooling system. With vehicle running, slightly loosen coolant reservoir cap — air burps out. Significant air in circuit.
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4. Service records show coolant replacement 2 weeks ago. Non-EV shop used a generic coolant fill procedure. Hyundai IONIQ 6 (E-GMP platform) requires a specific bleed sequence with the vehicle in a particular orientation and using the service mode coolant pump activation function.
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5. Perform Hyundai E-GMP coolant bleed procedure via GDS2: vehicle on level ground, coolant pump activated in service mode, all air purge ports opened in sequence.
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6. After full bleed: front motor coolant delta drops to 14°C under same load conditions.
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7. Highway test 35 minutes. P0C46 does not return. No power reduction events.
Resolution & Root Cause
Cooling system properly bled per Hyundai E-GMP procedure. Air pocket removed from front motor circuit. P0C46 resolved.
💡 Key Lesson
Hyundai IONIQ 6 E-GMP coolant service requires a specific bleed procedure via GDS2 service mode — it cannot be done by simply running the engine and squeezing hoses. P0C46 front motor only, appearing after coolant service, following sustained highway use = trapped air from improper bleed. This is a 45-minute procedure, not a drive unit replacement.
About This Case
This case was solved remotely by an HVDesk specialist with 15+ years of hands-on experience across major EV platforms including Tesla, Hyundai/Kia, Volkswagen ID series, BMW i-series, and Ford EVs. The procedure was provided as structured remote support to an independent auto repair shop.
