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Toyota fault codes: Common issues & troubleshooting
Toyota vehicles are known for their reliability, but even the most durable cars can show a check engine light from time to time. When that happens, it's important to understand the issue to keep your vehicle in great shape. Using a reliable diagnostic tool can help you easily find out what's happening under the hood and get back on the road.
In this article, we'll not only explain how a diagnostic tool can pinpoint the problem but also cover the most common Toyota fault codes, along with their causes and solutions.
What is a fault code?
A fault code, or diagnostic trouble code (DTC), allows your vehicle to report specific problems through its on-board computer. Each code identifies a problem within your vehicle's components, from a faulty sensor to an ignition system failure, to help you pinpoint the exact problem.
Fault codes fall into two main categories:
- Standard OBD2 codes: These universal codes apply to all makes and models of vehicles equipped with the OBD2 system. They cover systems related to vehicle emissions.
- Manufacturer-specific codes: Toyota and other brands use these codes to address problems that standard OBD2 codes don't cover, such as comfort and safety systems.
Toyota-specific codes address a much wider range of faults compared to general OBD2 codes. The chart below highlights the difference in their coverage.
Comparison of diagnostic fault code coverage: Generic OBD2 vs. Toyota-specific Codes
How to read Toyota fault codes
To access diagnostic trouble codes, you’ll need an OBD2 reader. While any standard OBD reader can provide generic fault codes, choosing one that also supports Toyota-specific codes will give you a more complete picture and make diagnostics more accurate.
While the procedure is similar for most OBD2 readers, here's how to scan trouble codes with OBDeleven:
1. Find the OBD2 port. Usually, you’ll find Toyota diagnostic port under the dashboard, in the driver's footwell.
2. Plug in the OBD2 reader.
3. Turn on the ignition. You don’t need to start the engine itself.
4. Connect your OBDeleven device to the app. Open the OBDeleven app and tap "Connect" in the center of the screen.
5. Scan the codes. Tap the scan button in the center of the screen and wait a few minutes while it reads your vehicle's systems.
6. Open the list of faults. Tap on any icon that has faults, or on the list of control units, and open each one that's marked as "Faulty."
7. Interpret the codes. Each fault code has a brief description. For more information, tap the "G" icon at the right. This will take you to Google results for the exact code for your car model.
Common Toyota fault codes
Some Toyota diagnostic codes are more common than others. Below, we have selected the most popular Toyota fault codes list among OBDeleven users and broken down each one, including what it means and what causes it.
Toyota fault code: P0420 and P0430 – Catalyst system efficiency below threshold
The P0420 code indicates that the catalytic converter on bank 1 isn't working as efficiently as it should, while the P0430 code reflects the same issue but on bank 2.
In some engine configurations, such as inline-6, V6, V8, V10, and W8, the exhaust system is divided into two banks. "Bank 1" refers to the bank on the side of the first cylinder, and "Bank 2" refers to the bank on the opposite side.
Exhaust system types. Source: densoautoparts.com
The catalytic converter is part of the exhaust system. It reduces harmful emissions by converting unburned fuel and carbon monoxide into carbon dioxide and water. It also changes nitrogen oxides back into nitrogen.
Two oxygen sensors monitor this process. One is placed before the converter and the other after it. If both sensors detect similar oxygen levels, the converter may not be working properly. This triggers a fault code and turns on the check engine light.
This problem frequently arises from exhaust system damage or fuel system issues, leading to insufficient oxygen leaving the catalytic converter.
Further reading: What makes the catalytic converter malfunction?
Symptoms of P0420 and P0430
- Check engine light is on
- Slight decrease in fuel efficiency
- Possible sulfur or rotten egg smell from the exhaust pipe
- Change in exhaust sound
- Engine self-preservation mode (limp mode)
Common causes of P0420 and P0430
- Incorrect fuel type
- Leaking fuel injectors
- Faulty fuel pump
- Clogged fuel filter
- Loose fuel tank cap
- Clogged air filter
- Malfunctioning mass airflow (MAF) sensor
- Worn spark plugs
- Faulty ignition coils
- Damaged wiring
- Bad or clogged catalytic converter
- Cracked exhaust manifold
- Exhaust leaks before the catalytic converter
- Faulty oxygen sensor
Toyota fault code: P2000 – NOX trap efficiency below threshold. Bank 1
The P2000 code indicates that the nitrogen oxide (NOX) trap on bank 1 isn't working efficiently. The NOX trap is part of the vehicle's emission control system that reduces the amount of harmful nitrogen oxides released into the atmosphere.
When this code appears, it can result in failed emissions test due to high NOX levels.
Symptoms of P2000
- Check engine light is on
Common causes of P2000
- Wiring issues
- Bad or clogged catalytic converter
- Faulty oxygen (O2) or NOX sensor
- Faulty mass air flow sensor
- Exhaust or intake leaks
- Engine control unit problems
Toyota Fault Code: P2004 - Intake manifold runner control solenoid stuck open. Bank 1
Code P2004 means that the intake manifold runner control (IMRC) on bank 1 is stuck in the open position. This valve controls the airflow into the engine, so if it's stuck, the engine can't properly control air intake.
The IMRC system operates based on engine speed. At low RPMs, it should close to increase air velocity and improve torque. If it stays open, the engine gets too much air, resulting in poor fuel efficiency and less power at low engine speeds.
Symptoms of P2004:
- Poor engine performance, particularly at low RPMs
- Increased fuel consumption
- Engine stalling or rough idling
- Check engine light is on
Common causes of P2004:
- Faulty IMRC solenoid
- Loose or sticking intake manifold runners
- Defective intake manifold runner position sensor
- Electrical issues in the IMRC actuator control circuit
- Bad manifold absolute pressure (MAP) sensor
- Clogged vacuum hoses
- Corrosion on the IMRC solenoid connector
Toyota fault code: P0171 and P0174 – Fuel trim system too lean
The P0171 trouble code indicates that your vehicle's engine runs too lean on bank 1, while the P0174 code signifies the same issue on bank 2. This means the air-fuel mixture contains too much air and not enough fuel.
The engine control unit (ECU) continuously monitors the air-fuel ratio to ensure optimal combustion. When the ratio becomes too lean, it triggers this fault code.
This issue typically arises due to problems in the fuel or air intake systems.
Symptoms of P0171 and P0174
- Engine stalling or rough idling
- Reduced power and poor acceleration
- Limp mode
- Difficulty starting the vehicle
- Check engine light is on
- Unusual engine noises, such as knocking or pinging
Common causes of P0171 and P0174
- Dirty or faulty mass air flow sensor
- Vacuum leak in the intake manifold, hoses, or positive crankcase ventilation (PCV) system
- Faulty oxygen sensor
- Clogged fuel injectors
- Dirty fuel filter
- Weak fuel pump or low fuel pressure
- Faulty fuel pressure regulator
- Exhaust leak before the O2 sensor
- Faulty boost pressure sensor
Toyota fault code: P3000 – HV battery malfunction
The P3000 code signals an issue with a Toyota hybrid vehicle's high-voltage (HV) battery. When this code appears, it typically means that the vehicle’s powertrain control module (PCM) has detected a malfunction in the hybrid battery system, which is critical for managing its electric power.
The HV battery supports the electric drive system, and any failure can significantly affect the vehicle's performance, including the ability to switch between electric and fuel modes. This issue often stems from a battery that isn't charged sufficiently or a more serious fault in the battery assembly itself.
Symptoms of P3000
- Check engine light is on
- Hybrid system warning light
- Reduced vehicle power
- Difficulties in starting the vehicle
Common causes of P3000
- Low fuel level
- Insufficiently charged HV battery
- Failure or deterioration of the high-voltage battery assembly
Toyota fault code: P0441 – Evaporative emission system incorrect purge flow
The P0441 code indicates that your vehicle’s evaporative emission control (EVAP) system has an incorrect purge flow. This happens when the system purges the incorrect amount of fuel vapor from the charcoal canister into the engine.
The EVAP system trapping fuel vapors in a charcoal canister prevents them from escaping into the atmosphere. The purge valve releases these vapors into the engine for combustion. When this process malfunctions, it triggers the
P0441 code.
Symptoms of P0441
- Check engine light is on
- Possible fuel smell around the vehicle
Common causes of P0441
- Faulty purge valve
- Clogged or disconnected purge lines
- Faulty purge valve solenoid
- Vacuum leaks
- Faulty purge flow sensor
- Faulty leak detection pump
- Electrical issues in the EVAP circuit
Toyota fault code: P0455 – Evaporative emission control system gross leak detected
The P0455 code indicates a heavy leak in the evaporative emission control system.
The vehicle's leak detection pump performs periodic tests to ensure that the EVAP system is sealed and functioning properly. If it detects a significant leak, it triggers code P0455 and illuminates the check engine light.
Symptoms of P0455
- Check engine light is on
- Fuel smell near the gas cap or inside the vehicle
Common causes of P0455
- Loose or damaged fuel cap
- Cracked or damaged EVAP hoses
- Faulty canister purge valve or vent valve
- Cracked fuel tank
- Malfunctioning EVAP leak detection pump
Toyota fault code: P0101 – Mass air flow circuit range/performance problem
The P0101 code indicates an issue with the MAF sensor, which measures the amount of air entering the engine. The engine’s computer uses this information to calculate the correct air-fuel mixture for optimal combustion. When the sensor detects an abnormal reading outside the expected range, it triggers the P0101 code.
The MAF sensor is critical to maintaining proper air-fuel ratios. When it fails to operate correctly, the engine may not receive the appropriate amount of air, leading to performance issues.
Symptoms of P0101
- Check engine light is on
- Poor fuel economy
- Rough idling or stalling
- Hesitation or loss of power during acceleration
- Black smoke from the exhaust
Common causes of P0101
- Dirty or contaminated MAF sensor
- Leaks in the intake manifold or air hoses
- Damaged or faulty MAF sensor
- Clogged or dirty air filter
- Faulty wiring
- Incorrect air filter installation
- Blockages in the air intake system
Toyota fault code: P0300 – Random/Multiple cylinder misfire detected
The P0300 code indicates that the engine is experiencing misfires in multiple cylinders. Misfires occur when the combustion process in a cylinder is incomplete. This issue often affects engine performance and emissions.
If the code appears with others, such as P0301, P0302, P0303, the last digit points to a specific cylinder.
Symptoms of P0300
- Rough idling
- Poor acceleration
- Reduced fuel efficiency
- Check engine light on
- Unusual engine sounds like knocking or pinging
Common causes of P0300
- Faulty spark plugs or wires
- Worn ignition coils
- Clogged fuel injectors
- Dirty fuel filter
- Vacuum leaks in the intake manifold
- Faulty crankshaft or camshaft position sensor
- Low fuel pressure
Toyota fault code: U0073 – Control module communication bus "A" off
Code U0073 indicates a communication problem in your Toyota's CAN (Controller Area Network) bus. This means that the control units, such as the engine or transmission, can't communicate with each other properly, which can cause malfunctions across multiple systems.
The CAN bus is a network that allows different modules in your vehicle to exchange information. It uses two wires, and the U0073 code specifically points to a problem with wire "A."
Symptoms of U0073
- Check engine light is on
- Reduced engine power
- Shifting issues in automatic transmission
- Increased fuel consumption
- Warnings on dashboard
- Difficulties to start the engine
- Various other symptoms
Common causes of U0073
- Faulty control module
- Damage in CAN bus wiring, corrosion, or poor connection
- Low battery voltage or power issues
Toyota fault code: P0125 – Insufficient coolant temperature for closed loop fuel control
Code P0125 indicates that the engine can't switch from open-loop to closed-loop fuel control because the coolant temperature is too low. In open-loop, the ECU is unable to use oxygen sensor data to manage the air-fuel mixture.
Symptoms of P0125
- Check engine light is on
- Poor fuel efficiency
- Insufficient heater operation
Common causes of P0125
- Faulty coolant temperature sensor
- Low or leaking coolant
- Stuck or malfunctioning thermostat
- Wiring issues
Toyota fault code: P0340 – Camshaft position sensor circuit malfunction
Code P0340 indicates a problem with the camshaft position sensor circuit. This sensor tracks the camshaft position and sends data to the ECU to control fuel injection and ignition timing. If the circuit fails, the ECU can't get accurate data, resulting in engine performance issues.
The camshaft and crankshaft sensors work together to keep the engine running smoothly.
Symptoms of P0340
- Check engine light is on
- Engine misfires or stalls
- Rough idling or poor acceleration
- Difficulties to start the engine
- Shifting issues in automatic transmission
Common causes of P0340
- Damaged or faulty camshaft position sensor
- Poor electrical connection to the camshaft sensor
- Issues with the crankshaft position sensor)
- Faulty ECU
Toyota fault code: P0500 – Vehicle speed sensor (VSS) Malfunction
The P0500 code means there’s a problem with the vehicle speed sensor (VSS). This sensor sends speed data to the engine, transmission, and other control units. When it fails, the ECU receives either no signal or an incorrect speed reading. This can affect systems that rely on this data, such as the speedometer, ABS, and cruise control.
In most vehicles, the VSS measures the speed of the transmission output shaft.
Symptoms of P0500
- Check engine light is on
- Malfunctioning speedometer or incorrect speed
- ABS and traction control system malfunction, warning lights
- Cruise control malfunction
- Shifting issues in automatic transmission
- Poor throttle response
Common Causes of P0500
- Faulty vehicle speed sensor
- Damaged wiring, corrosion, or poor connection
- Damaged drive gear
Toyota fault code: P2121 – Throttle/Pedal position sensor/switch "D" circuit range/performance
Code P2121 indicates a problem with the throttle pedal position sensor. This sensor communicates with the ECU to control engine power based on pedal position. If the sensor sends incorrect or inconsistent signals, the ECU triggers this code and limits engine power to prevent further damage.
Symptoms of P2121
- Check engine light on
- Reduced engine power
- Engine self-preservation mode (limp mode)
Common causes of P2121
- Faulty accelerator pedal position sensor
- Damaged wiring, corrosion, or poor connection
- Malfunctioning throttle control motor
- Issues with the ECU
- Damaged VSS drive gear
Disclaimer: Advice, how-to guides, and car care tips on our blog are intended as helpful resources for general maintenance and repairs. While we strive for accuracy, the information is provided to the best of our knowledge and
should be used at your own discretion and risk.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.