Common Reasons For Check Engine Light in Toyota

Most common reasons for check engine light in Toyota cars indicated about something went wrong in to the engine, sensors signal to the onboard system to inform the driver via engine check light. These listed Check engine sensor faults not only occur to Toyota but to all vehicles.

Toyota Common Check Engine Light issues:

  • MAP (Mass/Manifold Air Flow) Sensor Fault
  • Oxygen (Upstream O2) Sensor Fault
  • Catalytic Converter (Downstream O2) Sensor Fault
  • Hybrid Motor Sensor Fault
  • Knocking Sensor Fault
  • Coolant Temperature Sensor Fault
  • ABS Sensor Fault
  • Throttle Position (TP) Sensor Fault
  1. Map Sensors:

What are the symptoms of a faulty Map Sensor?

  • Uneven distribution of Fuel and Air mixture (Lean or Rich mixture).
  • Fuel average dropped or too much fuel consumption.
  • Jerk while acceleration
  • Miss Fire or called Rough Idle

How to Fix:

Map sensor usually be fix by using carburetor cleaner to clean the map sensor, but better to replace it.

How does a map sensor work?

Map Sensors usually installed in the fuel injector technology engines in which the Map function is to provide constant air pressure to the main system (ECU) and ECU then uses the data of map sensor and to determine and calculate the exact airflow pressure an engine require to get the optimum best combustion.

  1. Oxygen (Upstream O2) Sensor Fault

What are the Symptoms of a bad oxygen Sensor?

  • Engine Pinging
  • Inefficient Fuel mileage
  • Engine Missing
  • Rough idle

How does an oxygen sensor work?

O2 sensor measure the amount of concentration level of oxygen in the exhaust gas and in the air, Rich mixture demand more oxygen this would cause a buildup of volt due to transportation ions and lean mixture demand less oxygen this would cause to low down the volt. O2 provide real time data to ECU to determine and measure the exact amount of O2 in the gas to be able to perform efficiently.

How to Fix:

Replacement is the only option.

  1. Catalytic Converter (Downstream O2) Sensor Fault:

What are the symptoms of a bad catalytic converter?

  • Engine startup problem
  • Co2 Emission increased

How does a catalytic converter work?

Catalytic converter made from number of combination (platinum, palladium and rhodium), catalytic job is to filter all gasses coming from the engine into exhaust pipe before kicking out from the exhaust pipe, and this gadget is to reduce emission gas in order to save the environment from harmful gases. Catalytic converters also work hand-in-hand with a control system. This control system controls the fuel injection system and monitors the emissions leaving the engine before they enter the catalytic converter. It also contains an oxygen sensor, which detects how much oxygen is entering the exhaust system.

How to Fix:

Replacement required

  1. Knocking Sensor Fault:

What are the Symptoms of a faulty knocking Sensor?

  • Engine makes rattling or pinging noises
  • Slow car acceleration
  • Check engine light on

How does a knocking Sensor works?

Knocking sensor sense unusual vibration/pulsation caused by ignition and detonation in the engine, any abnormality detect by knocking sensor passed to the PCM System.

How to Fix:

Knocking sensor fault arises by many reason it could be low quality fuel used, sparking plug issue and knocking sensor itself have fault. Therefore better to consult a good mechanic.

  1. Coolant Temperature Sensor Fault:

What are the symptoms of a faulty coolant temperature sensor?

  • Engine overheating
  • Uneven fuel distribution causes high consumptions
  • Constant Black smoke from exhaust
  • Unadjusted Rpm
  • Check engine light on

How to Fix:

Coolant temperature sensor fault can be arises by thermostat wall been blocked or sensor itself. In both cases replacement needed.

How does a coolant temperature sensor work?

Coolant temperature sensor measuring the engine temperature from thermostats wall and coolant water and then passed to the ECU, ECU then adjust the fuel calculation and engine timing to its optimal level. A hot engine requires less fuel and cold engine requires more fuel.

  1. ABS Sensor Fault:

What are the symptoms of a faulty ABS sensor?

  • Check engine light on

How does ABS sensor work?

ABS or called wheel sensor monitor the speed of the wheel and send this information to the main ABS module system, Abs control unit uses the data as sent to prevent the brakes from locking in case of emergency stop.

How to Fix:

Cleaning of wheel sensors could remove the sensor fault.

  1. Throttle Position (TP) Sensor Fault

What are the symptoms of bad throttle positon sensor?

  • Slow Acceleration
  • Problem with gear shift up
  • Auto high and low speed while on the road
  • Check engine light on and off
  • Engine misfire

How does a Throttle position TP sensor work?

It is located on the butterfly spindle to monitor the throttle position, in addition TP is attached to the main car ECU system, any problem in the TP would affects the car performance entirely.

How to Fix:

Calibration required

Specific Sensor issues in Toyota Brands:

Check Engine Light Toyota Corolla:

  • Map sensor fault is the basic and most common problem have been seen in the Toyota corolla.
  • Coolant sensor fault is the second after map sensor have been seen in the Toyota corolla.

Check Engine Light Toyota Camry:

  • Camry do have problems with the Speed sensor and Oxygen sensor.

Check Engine Light Toyota Prius:

  • The most common problem in Prius is the Hybrid Motor sensor fault.


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