What is the 2001-2007 Toyota Highlander 2.4L 2AZ-FE Head Gasket and Head Bolt Thread Failure?

The 2001-2007 Highlander with the 2.4L 2AZ-FE 4-cylinder engine suffers from a design flaw where the aluminum head bolt threads strip out of the engine block. The plastic intake manifold traps heat against the block, causing thermal fatigue of the aluminum threads. This leads to… Repairs typically run $2,500-$5,000. Severity: high.

What is the 2006-2019 Toyota Highlander Hybrid Inverter Coolant Pump Failure (Inverter Overheat) — P0A05 / P0A93?

The Highlander Hybrid uses a dedicated electric water pump to circulate coolant through the power inverter/converter, which runs separately from the engine cooling system. The electric pump wears out and stops circulating coolant, allowing the inverter and hybrid electronics to o… Repairs typically run $700-$1,100. Severity: high.

What is the 2006-2013 Toyota Highlander Hybrid Brake Booster / ABS Actuator Assembly Failure (Accumulator Leak) — C1391?

The regenerative-braking brake actuator (the integrated ABS/booster/accumulator pump module) is a known weak spot on the Highlander Hybrid. The accumulator develops an internal leak and the pump runs constantly, triggering a loud, repetitive whirring/buzzing and warning lights; i… Repairs typically run $1,600-$3,500. Severity: high.

What is the 2001-2007 Toyota Highlander V6 Engine Oil Sludge / Gelling (1MZ-FE / 3MZ-FE) — Oil Pump Pickup Starvation?

The early Highlander 3.0L 1MZ-FE (and successor 3.3L 3MZ-FE) V6 is prone to engine oil sludge/gelling. Blow-by gases and moisture that fail to burn off (aggravated by short-trip driving, extended oil intervals and a PCV valve that clogs) turn the oil to a gel that coats the valve… Repairs typically run $500-$6,000. Severity: high.

What is the 2006-2019 Toyota Highlander HV Battery Cooling Fan and Intake Filter Clogged With Dust/Pet Hair — False Hybrid Battery Failure (P0A80 / P0A7F)?

The Highlander Hybrid cools its high-voltage battery by drawing cabin air through an intake located under the cargo floor, past a filter, through a blower and across the pack. Dust, lint and pet hair progressively clog the filter and cake the fan blades. Airflow drops, cells run… Repairs typically run $60-$400. Severity: medium.

What is the 2001-2016 Toyota Highlander Catalytic Converter Efficiency Failure — P0420 / P0430 Check Engine Light?

A very common Highlander check-engine complaint is P0420 (Catalyst Efficiency Below Threshold, Bank 1) and its Bank 2 twin P0430. The downstream oxygen sensor readings track the upstream sensor too closely, indicating the catalytic converter is no longer scrubbing exhaust efficie… Repairs typically run $200-$2,500. Severity: medium.

Toyota · Known Issues

2006 Toyota Highlander Problems: 9 Known Issues

2006 model year · 1,200+ owner reports · Updated September 2026

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According to Au7o's analysis of 1,200+ owner reports, the 2006 Toyota Highlander has 9 documented known issues, with 7 rated critical. The most serious are Hybrid Battery Pack Degradation and Failure ($1,500-$5,500 repair), 2.4L 2AZ-FE Head Gasket and Head Bolt Thread Failure ($2,500-$5,000 repair), Hybrid Inverter Intelligent Power Module (IPM) Transistor Solder Failure — Hybrid System Shutdown/Stall (Recall 13V396000) ($0-$4,500 repair), Hybrid Inverter Coolant Pump Failure (Inverter Overheat) — P0A05 / P0A93 ($700-$1,100 repair), Hybrid Brake Booster / ABS Actuator Assembly Failure (Accumulator Leak) — C1391 ($1,600-$3,500 repair), Radiator Internal Transmission-Cooler Failure — ATF/Coolant Cross-Contamination ("Strawberry Milkshake") ($400-$4,500 repair) and V6 Engine Oil Sludge / Gelling (1MZ-FE / 3MZ-FE) — Oil Pump Pickup Starvation ($500-$6,000 repair). The most commonly reported issue is Hybrid Battery Pack Degradation and Failure with 1,200 owner reports.

Frequently Asked Questions

What are the most common Toyota Highlander problems?

According to Au7o's analysis of 1,200+ owner reports, the 2006 Toyota Highlander has 9 documented issues. The most frequently reported are: Hybrid Battery Pack Degradation and Failure, 2.4L 2AZ-FE Head Gasket and Head Bolt Thread Failure, Hybrid Inverter Intelligent Power Module (IPM) Transistor Solder Failure — Hybrid System Shutdown/Stall (Recall 13V396000). Of these, 7 are rated critical and should be addressed promptly.

Is the Toyota Highlander reliable?

The 2006 Toyota Highlander has 9 known issues documented across 1,200+ owner reports. 7 issues are rated critical: Hybrid Battery Pack Degradation and Failure and 2.4L 2AZ-FE Head Gasket and Head Bolt Thread Failure and Hybrid Inverter Intelligent Power Module (IPM) Transistor Solder Failure — Hybrid System Shutdown/Stall (Recall 13V396000) and Hybrid Inverter Coolant Pump Failure (Inverter Overheat) — P0A05 / P0A93 and Hybrid Brake Booster / ABS Actuator Assembly Failure (Accumulator Leak) — C1391 and Radiator Internal Transmission-Cooler Failure — ATF/Coolant Cross-Contamination ("Strawberry Milkshake") and V6 Engine Oil Sludge / Gelling (1MZ-FE / 3MZ-FE) — Oil Pump Pickup Starvation. Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.

How much does it cost to fix common Toyota Highlander problems?

Repair costs for known Toyota Highlander issues range from $0 to $6,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Hybrid Battery Pack Degradation and Failure, typically costs $1,500-$5,500 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.

What is the 2006-2013 Toyota Highlander Hybrid Battery Pack Degradation and Failure?

Highlander Hybrid NiMH battery packs degrade over time, with individual cells failing after 8-12 years or 150,000+ miles. Failed cells cause reduced fuel economy, loss of hybrid assist, and eventual inability to start the vehicle. Repairs typically run $1,500-$5,500. Severity: high.

All 9 Known Issues

Other Toyota Models

Frequently Asked Questions

What are the most common Toyota Highlander problems?

Is the Toyota Highlander reliable?

How much does it cost to fix common Toyota Highlander problems?

What is the 2006-2013 Toyota Highlander Hybrid Battery Pack Degradation and Failure?

2006-2013 Toyota Highlander: Hybrid Battery Pack Degradation and Failure#

2006-2010 Toyota Highlander: Hybrid Inverter Intelligent Power Module (IPM) Transistor Solder Failure — Hybrid System Shutdown/Stall (Recall 13V396000)#

2006-2019 Toyota Highlander: HV Battery Cooling Fan and Intake Filter Clogged With Dust/Pet Hair — False Hybrid Battery Failure (P0A80 / P0A7F)#

2001-2007 Toyota Highlander: 2.4L 2AZ-FE Head Gasket and Head Bolt Thread Failure#

2001-2007 Toyota Highlander: V6 Engine Oil Sludge / Gelling (1MZ-FE / 3MZ-FE) — Oil Pump Pickup Starvation#

2006-2019 Toyota Highlander: Hybrid Inverter Coolant Pump Failure (Inverter Overheat) — P0A05 / P0A93#

2001-2013 Toyota Highlander: Radiator Internal Transmission-Cooler Failure — ATF/Coolant Cross-Contamination ("Strawberry Milkshake")#

2006-2013 Toyota Highlander: Hybrid Brake Booster / ABS Actuator Assembly Failure (Accumulator Leak) — C1391#

2001-2016 Toyota Highlander: Catalytic Converter Efficiency Failure — P0420 / P0430 Check Engine Light#