Most Common Acura Check Engine Codes (TL, MDX, RDX, TSX, and Integra)

Understanding Acura Check Engine Codes

Acura is Honda's luxury division, and every Acura model shares its platform, engines, and electronics with Honda vehicles. The MDX and RDX share drivetrains with the Honda Pilot and CR-V. The TL and TSX use Honda's J-series V6 and K-series four-cylinder engines, respectively. The new Integra shares its 1.5L turbocharged engine with the Honda Civic. Because Acura and Honda share most engines and platforms, most check engine codes and fixes match across both brands -- though Acura-exclusive systems (SH-AWD-specific logic, and the first-generation RDX's unique 2.3L turbo engine that was never sold in a contemporary Honda) can generate codes with no Honda equivalent. Acura vehicles are known for their reliability, and most check engine codes are related to emissions components (oxygen sensors, catalytic converters, EVAP system) rather than mechanical failures. Acura-branded parts from the dealer carry a premium over Honda parts, but aftermarket options are identical since the components are the same.

P0135 -- O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

P0135 indicates the heater element in the upstream oxygen sensor on Bank 1 has failed. The heater element warms the sensor quickly on cold starts so the ECU can enter closed-loop fuel control sooner. On the TL and MDX with the J-series V6 (3.2L, 3.5L, 3.7L), the Bank 1 upstream oxygen sensor is located on the rear exhaust manifold, making it harder to access. The sensor costs $40-$80 for an aftermarket Denso or NTK unit (Honda's OEM suppliers). On the TSX with the K-series four-cylinder, the sensor is more accessible on the front of the engine. On the RDX with the 2.0L turbo (2019+) or the older 2.3L turbo, the sensor is positioned after the turbocharger. Always use Denso or NTK sensors on Honda/Acura vehicles, as cheap universal sensors have a high failure rate due to the ECU's tight fuel trim tolerances.

P0141 -- O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

P0141 is the downstream counterpart to P0135, indicating the heater element in the rear oxygen sensor on Bank 1 has failed. The downstream sensor monitors catalytic converter efficiency and does not affect fuel mixture. On the TL and MDX with the V6, the downstream sensor is located after the catalytic converter and is typically more accessible than the upstream sensor. The sensor costs $35-$70 aftermarket. P0141 appearing alongside P0135 on a higher-mileage Acura usually means both sensors have reached end of life simultaneously, which is common since they are exposed to the same exhaust conditions. Replace both sensors at the same time to avoid a return trip. On the TSX, the downstream sensor is easily accessible from underneath the vehicle.

P0171 -- System Too Lean (Bank 1)

P0171 on Acura vehicles indicates a lean fuel condition on Bank 1. On the TL and MDX with the J-series V6, the most common cause is a dirty or failing mass airflow sensor. Honda/Acura MAF sensors are sensitive to contamination from oiled aftermarket air filters (like K&N filters) -- over-oiling the filter can coat the MAF sensor element. Clean the MAF sensor with dedicated MAF cleaner ($8-$12) before replacing it ($60-$100). On the TSX with the K-series engine, P0171 can be caused by a cracked intake manifold gasket or a failing PCV valve. On the RDX with the turbo engine, check the charge pipe connections and intercooler hoses for boost leaks. On all Acura models, a vacuum leak at the brake booster hose is a common cause that is easy to overlook during diagnosis.

P0300 -- Random/Multiple Cylinder Misfire Detected

P0300 on the Acura TL and MDX with the J-series V6 is commonly caused by worn spark plugs or failing ignition coils. Honda's condition-based Maintenance Minder system (rather than a single fixed mileage) governs the plug interval on the J-series, but misfires can appear starting around 80,000 miles. NGK or Denso iridium plugs ($8-$15 each) are the OEM-equivalent choice. Ignition coils cost $30-$50 each aftermarket. On the V6, the rear bank spark plugs and coils are difficult to access, adding significant labor time. On the TSX with the K-series four-cylinder, P0300 is less common but can be caused by a failing ignition coil or carbon buildup on the intake valves (particularly on direct-injection models). On the new Integra with the 1.5L turbo, carbon buildup from direct injection can cause misfires after 60,000 miles -- walnut blasting the intake valves ($300-$500) is the recommended cleaning method.

P0420 -- Catalyst System Efficiency Below Threshold (Bank 1)

P0420 on Acura vehicles typically appears between 120,000 and 180,000 miles, which is longer than many competitors thanks to Honda's efficient combustion. On the TL and MDX with the V6, the catalytic converter is located downstream of the exhaust manifold. OEM converters are expensive ($800-$1,500), but quality aftermarket options from Eastern Catalytic or Walker are available for $250-$500. On the TSX with the K-series engine, the catalytic converter is integrated into the exhaust header on some model years, making replacement more expensive ($600-$1,000). Before replacing the converter, always check the downstream oxygen sensor ($40-$70) -- a slow-responding sensor can trigger P0420 without actual converter degradation. On any Acura with persistent misfires or oil consumption, fix those issues first before replacing the converter, as they will damage a new converter.

P0443 -- EVAP Purge Control Valve Circuit

P0443 indicates an electrical problem with the EVAP purge control solenoid circuit. On the TL and MDX, the purge solenoid is located on or near the intake manifold and costs $30-$50 aftermarket. On the TSX and Integra, the purge solenoid is in a similar location and is easily accessible. Before replacing the solenoid, check the electrical connector for corrosion or damage -- a poor connection can trigger the circuit code without the solenoid actually being bad. On all Acura models, the solenoid wiring harness can chafe against nearby engine components, causing intermittent circuit faults. P0443 does not affect drivability but will prevent passing an emissions test.

P0455 -- EVAP System Large Leak Detected

P0455 indicates a significant leak in the evaporative emissions system. On all Acura models, the gas cap is the first thing to check. Honda/Acura gas caps use a specific seal design, and aftermarket replacement caps sometimes do not seal properly. Use a genuine Honda/Acura replacement cap ($15-$25) to ensure a proper seal. On the MDX and RDX, the EVAP canister vent shut valve is located near the charcoal canister under the vehicle and can fail from road debris or corrosion exposure. The valve costs $40-$60. On the TL, the EVAP canister vent shut valve can corrode and stick, causing a large leak. On the TSX, the fuel tank pressure sensor ($30-$50) can misread tank pressure and trigger P0455. A smoke test ($80-$150) is the most reliable way to identify the exact leak location.

P0497 -- EVAP System Low Purge Flow

P0497 indicates the EVAP system purge flow is lower than expected, meaning fuel vapors are not being drawn from the charcoal canister into the engine at the expected rate. On the TL and MDX, this is commonly caused by a failing purge control solenoid valve that is stuck closed or partially restricted. The valve costs $30-$50 and is located on or near the intake manifold. On the TSX, a blocked or kinked EVAP hose between the canister and the purge valve can restrict flow. On the RDX, the charcoal canister itself can become saturated or restricted, especially if the vehicle has been topped off repeatedly at the gas pump (overfilling pushes liquid fuel into the canister). P0497 does not affect drivability but will fail an emissions test.

P0740 -- Torque Converter Clutch Circuit Malfunction

P0740 is a well-known code on Acura TL and MDX models and indicates a problem with the torque converter clutch (TCC) circuit. On the 2004-2008 TL with the 5-speed automatic transmission, P0740 is frequently caused by the transmission's third gear pressure switch or the TCC solenoid valve. The torque converter clutch is known to shudder on these models, and the condition can eventually trigger P0740. A transmission fluid change using only Honda DW-1 ATF ($7-$9 per quart, roughly 3-3.3 quarts for a typical drain and fill) can resolve early-stage TCC issues. On the MDX with the 5-speed or 6-speed automatic, P0740 is often related to the lock-up clutch wearing out, requiring torque converter replacement ($500-$800 for the converter plus $800-$1,500 in labor). On the TSX with the 5-speed automatic, P0740 is less common but the same fluid maintenance applies.

P1259 -- VTEC System Malfunction

P1259 is a Honda/Acura-specific manufacturer code indicating a problem with the VTEC (Variable Valve Timing and Lift Electronic Control) system. On the TL with the J-series V6, this code commonly points to the VTEC solenoid or its oil pressure switch. The VTEC solenoid controls oil flow to engage the high-performance cam profiles above certain RPMs. Low oil level or dirty oil is the most common root cause, as the VTEC system requires adequate oil pressure to function. The VTEC solenoid itself costs $50-$100 and the pressure switch costs $20-$30. On the TSX with the K-series engine, the VTEC solenoid is located on the back of the cylinder head. On the Integra (older B-series engines), the VTEC solenoid gasket can leak oil, reducing pressure to the system. Always check oil level and condition before replacing VTEC components -- a simple oil change resolves P1259 in many cases.

Acura Model-Specific Issues

The TL (1999-2014) is one of Acura's most popular models. The 2004-2008 TL with the J32A3 V6 is known for automatic transmission issues, particularly torque converter shudder and third gear wear. Regular transmission fluid changes every 30,000 miles are critical. The MDX (2001-present) shares its V6 drivetrain with the Honda Pilot and is generally reliable, though the 2001-2006 models share the same transmission concerns as the TL. The RDX (2007-present) has been reliable across all generations. The first generation (2007-2012) used a unique 2.3L turbo four-cylinder (K23A1) with no contemporary Honda equivalent; anecdotal owner reports mention turbo bearing wear but no confirmed mileage pattern is documented. The TSX (2004-2014) uses the K-series four-cylinder and is one of the most reliable Acura models. The new Integra (2023-present) uses the 1.5L turbo shared with the Civic and is too new for long-term reliability data, but the platform is proven. Acura's SH-AWD system is reliable and does not typically generate check engine codes, though the rear differential fluid should be changed every 30,000 miles.

DIY Tips for Acura Owners

Acura vehicles are among the most DIY-friendly luxury cars available. The engine bays are well-organized with good access to most components. The K-series four-cylinder in the TSX and Integra has excellent accessibility for spark plugs, sensors, and ignition work. The J-series V6 in the TL and MDX has tighter access to the rear bank but is still manageable for most DIY work. For OBD-II scanning, any standard scanner reads Acura powertrain codes, but Honda's HDS (Honda Diagnostic System) provides dealer-level access to all modules. For an affordable alternative, the Carista OBD2 adapter ($30) with the Carista app provides enhanced Honda/Acura diagnostics and module coding. For parts, always use Denso or NGK for sensors and spark plugs (they are Honda's OEM suppliers). Honda DW-1 ATF is the only recommended transmission fluid for automatic Acura transmissions -- do not use generic ATF. Join acurazine.com for the most comprehensive Acura DIY community online.

Frequently Asked Questions