Toyota Engine Trouble Codes and What They Mean
Is your Toyota’s check engine light on? Don’t panic—it could be pointing to a Diagnostic Trouble Code (DTC) that helps identify the problem. In this blog post, we break down some of the most common Toyota engine trouble codes, explain their meanings, and explore potential causes. Whether it’s a lean fuel mixture, a misfire, or an EVAP system issue, understanding these codes can save you time and money. Perfect for DIY enthusiasts and curious car owners, this guide empowers you to take the first steps toward diagnosing and fixing your vehicle.
When your Toyota’s check engine light turns on, it’s often linked to a Diagnostic Trouble Code (DTC). Understanding these codes can save time and money by identifying potential issues early. Below are some of the most common Toyota engine trouble codes and what they signify:
When a light appears on your Toyota’s dashboard, it means the engine control module (ECM) has detected an issue and recorded it as an engine trouble code. These codes can be a bit puzzling, but the list below offers a helpful starting point for understanding potential problems with your vehicle when a specific code is triggered. While it’s not an exhaustive list, it’s a great resource to begin troubleshooting.
P0100 – Mass Air Flow Circuit
This basically indicates a problem with the the MAF sensor or circuit. The MAF may be disconnected, the wiring to the MAF may be bad, or the MAF sensor could be faulty.
Possible Solutions:
Check the wiring and connection for the MAF
Unplug and reconnect the MAF wiring harness
Check the voltage of the MAF sensor
Replace/repair any faults found
P0101 – Mass Air Flow Circuit Range/Performance
This code is triggered when high or low voltage is sent to the engine control module (ECM) from the mass air flow (MAF) sensor.
Likely causes:
Faulty MAF
Dirty MAF
Air intake system leaks
MAF harness is open or shorted
MAF circuit has a poor electrical connection
P0105 – Manifold Absolute Pressure Circuit
Those code is detected when excessively low or high voltage is sent from the manifold absolute pressure sensor to the ECM.
Most common causes:
Faulty sensor
Open or short in the sensor’s harness
Poor electrical connection from the sensor
P0106 – MAP/BARO Circuit Range/Performance
When excessively high or low voltage is sent from the manifold absolute pressure sensor, this code is triggered.
Causes include:
Faulty sensor
Harness for sensor is open or shorted
The electrical connection with the sensor is poor
Leaking or damaged vacuum line
P0110 – Intake Air Temperature Circuit
Excessively high or low voltage from the intake air sensor (IAT) will trigger this code.
Possible causes:
Faulty IAT sensor
Dirty air filter
There’s a short in the IAT sensor harness
The electrical connection with the IAT sensor’s circuit is poor
P0115 – Engine Coolant Temperature Circuit
When voltage from the engine coolant temperature (ECT) sensor is very low or high, this code will be triggered. This is usually due to low coolant level or a faulty ECT sensor. Other causes include a bad thermostat or problems with the sensor’s wiring harness.
Common causes:
Low engine coolant level
Faulty ECT sensor
Faulty thermostat
Short or poor electrical connection in the ECT sensor harness
P0116 – Engine Coolant Temperature Range/Performance
When the data sent to the ECM about the coolant temperature is not within the specified range, this code will appear. In most cases, the sensor or connections to it are bad, coolant is low, or the engine thermostat is faulty. Check the coolant first, then test the voltage of the sensor to narrow down is the problem is related to the sensor or the thermostat.
P0120 – Throttle Pedal Sensor Switch “A” Circuit
This is a very common Toyota code. Try cleaning the throttle body and resetting the light, then waiting to see if it comes back before taking further action. Should it come back, you will need to replace the throttle position sensor.
P0121 – Throttle Pedal Sensor Switch “A” Circuit Range/Performance
This code is triggered when a malfunction is detected due to extremely low or high voltage from the sensor. The sensor responds to accelerator pedal movement.
Possible causes of malfunction include:
Bad throttle position sensor (TPS)
Short in the TPS
Poor electrical connection with the TPS
Problems with the ECM (very uncommon)
P0125 – Insufficient Coolant Temperature for Closed Loop Fuel Control
The ECM monitors engine coolant temperature through a sensor after start-up. If no information is coming from the sensor after the engine is warmed up, this will trigger the code P0125. Possible causes include low coolant, stuck or bad thermostat, or faulty sensor.
P0130 – Heated Oxygen Sensor Circuit – Bank 1 Sensor 1
This trouble code is usually triggered when the O2 sensor in position bank 1, sensor 1 is bad or has faulty wiring. Replacing the sensor will almost always get rid of the code.
Other causes include:
Inadequate fuel pressure
Bad fuel injectors
Leaks in the air intake
Exhaust leaks
P0133 – Heated Oxygen Sensor Circuit Slow Response Bank 1 Sensor 1
This trouble code is triggered when there is a problem with the front oxygen sensor on bank 1. This code indicated the air fuel ratio is not being adjusted once the engine is at operating temperature. Most of the time, the oxygen sensor is faulty or the wiring to the sensor is frayed – an exhaust leak may also be present.
P0135 – Heated Oxygen Sensor Circuit – Bank 1 Sensor 1
This code indicates a problem with the front oxygen sensor on bank 1. When this code is triggered, the O2 heater element resistance is high. To repair the problem, you must repair the damage i the wiring harness, harness connectors, or replace the oxygen sensor.
P0136 – Heated Oxygen Sensor Circuit – Bank 1 Sensor 2
This code indicates a problem with the rear oxygen sensor on bank 1. When this code is triggered, the O2 heater element resistance is high. To repair the problem, you must repair the damage i the wiring harness, harness connectors, or replace the oxygen sensor.
P0153 – Heated Oxygen Sensor Circuit Slow Response – Bank 2 Sensor 1
This trouble code is triggered when there is a problem with the rear oxygen sensor on bank 1. This code indicated the air fuel ratio is not being adjusted once the engine is at operating temperature. Most of the time, the oxygen sensor is faulty or the wiring to the sensor is frayed – an exhaust leak may also be present.
P0170 – Fuel Trim Malfunction
When the fuel system is not operating properly, or the fuel in the mixture ratio is not correct, this code with be triggered. The most common causes are a dirty air filter, dirty MAF or air filter housing, or faulty MAF.
P0171 – System Too Lean Fault
This is one of the most common trouble codes in V-6 and larger engines. P0171 is a “System Too Lean (Bank 1),” which is triggered by the first exhaust oxygen (02) sensor (aka upstream 02 sensor) on the “Bank 1” side of the engine (designated as whichever side has cylinder number one).
P0401 – EGR Flow Insufficient
When your Toyota gives you a P0401 code, the technical issue is insufficient EGR flow. Like most engine trouble codes, the root cause may or may not be obvious.
The exhaust gas recirculation (EGR) system is part of your Toyota’s emissions system. It helps to reduce combustion temperatures. When a P0401 code occurs, you’ll likely notice a pinging or knocking when the vehicle is at higher speeds or when the engine is under load.
P0420 – Catalyst System Efficiency Below Threshold Error
Error code P0420 – or Catalyst System Efficiency Below Threshold (Bank 1) – is one of several trouble codes that fall into the general exhaust system code block. All P042X codes (where “X” can be any number) refer to the catalytic converter and exhaust system. P0420 refers to the catalytic converter or – more specifically – the oxygen (O2) sensors before and after it on the bank 1 side of the exhaust system.
Likely causes:
Leaded fuel in an unleaded system will nearly always trigger this, given the differing properties of leaded fuel combustion and exhaust.
Failed O2 sensors or connections are also possible culprits.
A failed catalytic converter.
Other less likely problems: an issue with the coolant temperature sensor, an exhaust manifold leak, a spark timing issue, leaking fuel injectors, misfires, or fuel oil contamination.
P0440 – EVAP Control System Malfunction
OBD-II code P0440 represents a general fault in the Evaporative Emission Control (EVAP) System.
Basically, this code means that something in the EVAP system is broken. Another code will typically accompany P0440, often in the P044X chain (where “X” represents any number). This code is most often triggered by:
A faulty or leaking gas cap.
A failed purge solenoid.
A plugged canister.
P0441 – Evaporative Emission Control (EVAP) System Fault
The P0441 OBD-II code is relatively rare (at least for Toyotas). It indicates an Evaporative Emission Control System Incorrect Purge Flow.
It usually indicates a bad vacuum switch or a leak in the EVAP system that is preventing fuel vapors from reaching the canister. The P0441 code can also indicate a faulty or “stuck” PCV, a short circuit in the feed circuit, or a faulty purge solenoid.
Check the wiring and connection for the MAF
Unplug and reconnect the MAF wiring harness
Check the voltage of the MAF sensor
Replace/repair any faults found
P0442 – Small EVAP System Leak Detected
Probably the most common Evaporative Emission Control System (EVAP) related code on a Toyota, P0442 signifies that a small leak has been detected.
Most likely, the engine control module has found detected a fuel vapor leak in the EVAP control system that’s so small it’s not likely an indication of a major failure. A pinhole leak somewhere before the purge control valve (PCV) that causes a loss of vacuum pressure can be enough to trigger a P0442.
P0446 – EVAP System Control Circuit Malfunction
The P0446 OBD-II code often triggers with other related EVAP codes (like P0441), and the specific combination of codes can give your mechanic a better idea of where the actual problem lies.
P0402 – Excessive EGR Flow Malfunction
P0402 is the “Exhaust Gas Recirculation Flow Excessive Flow Detected” code, and it’s basically the opposite of a P0401 code. Whereas a P0401 means there is too little exhaust gas recirculation (EGR) happening. A P0402 means there is too much. This results in an overly-rich mixture of oxygen in the fuel/air mix and – as a result – higher engine temperatures.
Check the wiring and connection for the MAF
Unplug and reconnect the MAF wiring harness
Check the voltage of the MAF sensor
Replace/repair any faults found
P1135 – Air/Fuel Sensor Heater Circuit Response – Bank 1, Sensor 1
When the ECM detects that there is a heated oxygen sensor heater circuit that has malfunctioned, it will send out a P1135 code.
Most likely causes include:
The air/fuel ratio sensor bank 1 sensor 1 may be faulty.
There may be an open harness or a short on the air/fuel sensor bank 1 sensor 1.
There may be a poor electrical connection in the circuit to the air/fuel sensor bank 1 sensor 1.
The ECM may be faulty.
P1155 – Air/Fuel Sensor Heater Circuit – Bank 2, Sensor 1
OBD-II code P1155 represents a malfunction in the air/fuel sensor heater circuit for bank 2, sensor 1. Most often this code is a result of these problems:
Faulty air/fuel ratio sensor in bank 2, sensor 1.
Air/fuel sensor harness for bank 2, sensor 1 has a short or isn’t properly connected.
Air/fuel sensor for bank 2, sensor 1 has a poor electrical connection.
The ECM is faulty.
P1200 – Fuel Pump Relay/ECU Circuit Malfunction
Possible causes:
Faulty fuel pump relay.
Fuel pump relay sensor harness is open or shorted.
Fuel pump relay circuit poor has electrical connection.
Consider visually inspecting the wiring harness and the associated connectors, checking for damaged components, and looking for broken, bent, pushed, or corroded connector pins.
P1226 – Closed Throttle Position Learning Performance Problem
OBD-II code P1226 represents a problem with the closed throttle position learning performance of your vehicle. The electronic throttle control actuator is made up of the throttle control motor, throttle position sensor, and other components in this system. The throttle position sensor, or TPS, is meant to respond to movement in the throttle valve.
Possible causes of the P1226 code include:
Faulty electric throttle control actuator, throttle position sensor 2.
Faulty throttle control actuator harness is open or shorted, throttle position sensor 2.
Electric throttle control actuator circuit has a poor electrical connection, throttle position sensor 2.
P1228 – Fuel Pump Malfunction
This code is triggered when there is a problem with the function of your vehicle’s fuel pump. When P1228 is present in your vehicle’s ECM, it will prompt the illumination of your SES or check engine light.
The most common causes of this code are:
Faulty fuel pump
Unplug and reconnect the MAF wiring harness
Faulty fuel pump wiring harness
Faulty suction control valve, or SCV
Clogged fuel injectors
P1229 – Fuel System Over Pressure Fault
When there is a problem with pressure in the system, a trouble code from the vehicle’s ECM is stored; when the problem is too much pressure, the dashboard will illuminate the SES or check engine light to indicate that code P1229 has been stored in your vehicle’s ECM.
P1250 – Turbocharger System Malfunction
OBD-II code P1250 indicates a problem with the turbocharger system on your vehicle. On vehicles equipped with turbocharger systems, this code can indicate a problem within the system that is causing it to not function as it should.
Common causes of this code include:
Faulty vacuum sensing valve
Stuck turbo wastegate actuator
Faulty SCV valve
Wiring leading to the system
P1251 – Turbocharger Engine Boost Condition Fault
More times than not, the problem that throws this code is with the turbo solenoid valve. Mounted on the driver’s side of the engine near the top, it is a small cylinder-shaped plastic unit. This valve also has two vacuum hoses and an electrical connector. This valve operates the waste gate for the turbo and when faulty, it will cause the turbo to over or undercharge.
P1300 – Igniter Circuit Malfunction
The P1300 code is a diagnostic trouble code that refers to a problem with the igniter circuit.
There are several possible causes for this code, and the most common ones are damage to the wiring or connectors, a defective ignition coil, or a broken lighter.
P1310 – Igniter Circuit Malfunction
This code refers to a malfunction in the ignition system, with the malfunction being the lack of an IGF (Ignition Feedback) signal between the igniter (also known as an “ignition module”), and the PCM (Powertrain Control Module).
P1335 – Crankshaft Position Sensor Circuit Fault
A common cause of code P1335 is the failure of P1335 Crankshaft Position Sensor, but there are several other possible causes as well, such as:
Faulty crankshaft position sensor.
Crankshaft position (CKP) sensor harness is open or shorted.
Crankshaft position (CKP) sensor circuit has poor electrical connection.
P1349 – Variable Valve Timing System Malfunction
OBD-II code P1349 indicates a problem with the variable valve timing system in your Toyota, which is responsible for controlling and adjusting the intake valve timing according to driving conditions.
Possible causes of trouble code P1349 include:
Low or dirty engine oil.
Incorrect valve timing.
Faulty oil control valve.
Faulty variable valve timing controlled assembly.
Faulty engine control module (ECM).
P1400 – Sub-Throttle Position Sensor Circuit Fault
OBD-II code fault code P1400 occurs after a cold start is discovered, diagnostics are run, and if the actual exhaust power model does not match the expected exhaust power model.
Engine idle speed is high during a cold start – and the spark timing is delayed, allowing the catalyst to heat up faster.
Possible symptoms include:
The check engine lamp is lit.
After a cold start, the car’s RPM drops to the point that it tries to shut down.
P1410 – EGR Valve Position Sensor Circuit Malfunction
This code is most often caused by and Exhaust Gas Recirculation (EGR) Valve Position Sensor being stuck open or closed.
Usually replacing the EGR Valve Position Sensor takes care of the problem. The sensor is located on top of the EGR valve.
P1500 – Vehicle Speed Sensor Function Intermittent
The P1500 code Indicates the Vehicle Speed Sensor (VSS) input signal was intermittent.
This P1500 code is set when a VSS concern interferes with other On-Board diagnostics (OBD) tests, such as the catalyst efficiency monitor, the EVAP monitor or the HO2S monitor.
P1520 – Intake Manifold Runner Control Circuit Fault
The P1520 code occurs when the intake manifold runner control actuator harness is open or shorted. Other possible causes include:
Faulty Intake Manifold Runner Control (IMRC) actuator.
Intake Manifold Runner Control actuator harness is open or shorted.
Intake Manifold Runner Control actuator circuit poor electrical connection.
Faulty Powertrain Control Module (PCM).
P1565 – Faulty Cruise Control Main Switch
The P1565 code occurs when the cruise control main Switch circuit has a malfunction. Some possible causes for this code are:
A faulty Cruise Control Main Switch.
The cruise control main switch harness is open or shorted.
The cruise control main switch circuit has poor electrical connection.
P1600 – ECM or Battery Circuit Fault
A P1600 code is a generic code that is set in the engine computer to tell you that there is a Hybrid system problem – most likely a ECM or battery malfunction.
P1630 – Skid Control ECU / (ECM) Harness Is Open Or Shorted
The Skid Control Electronic Control Unit (ECU) sends signals such as cruise control cancel demand signals and brake operation demand from Engine Control Module (ECM) response signals to the ECM when the cruise control system is in operation.
Possible causes include:
Skid Control ECU / Engine Control Module (ECM) harness is open or shorted
Skid Control ECU / Engine Control Module (ECM) circuit poor electrical connection
Faulty Skid Control ECU
Faulty Engine Control Module (ECM)
P1603 – TCU Communication Error
When it comes to CAN (control area network) communication, all of the information communicated is done alone control modules like the ECM and TCM using CAN lines. When there is a problem with these lines, the ECM will detect the problem and store a P1603 trouble code; the storing of the trouble code is what causes the SES or check engine light to illuminate on the dash.
Possible causes of trouble code P1603 include:
Faulty transaxle control module (TCM)
Faulty engine control module (ECM)
Harness running from the TCM to the ECM has a short
There is a poor electrical connection between the TCM and ECM
P1656 – Oil Control Valve Circuit Malfunction
Code P1656 occurs when the Oil Control Valve (OCV) circuit has poor electrical connection or faulty Engine Control Module (ECM) connection.
P1780 – Park/Neutral Position Switch Malfunction
Code P1780 occurs when there’s an error with how the Park/Neutral Position (PNP) switch detects the shift lever position and sends signals to the Engine Control Module.
P2121 – Throttle/Pedal Position Sensor Error
The accelerator pedal position sensor is located on the accelerator pedal bracket. This pedal position sensor has two sensor elements and two signal outputs which are VPA & VPA2. VPA is there to detect problems in the VPA.
P2770 – Oxygen Sensor Stuck Lean Fault
When the trouble code, P2770 is stored in your Toyota’s ECM, the reading is stuck at lean for that sensor and the ECM can no longer accurately regulate the air/fuel ration. The occurrence of the code P2270 will cause a check engine light or SES light to illuminate on your dash.
