Fault code B1421 – solar sensor circuit (passenger side)

Fault code B1421 is called “Solar Sensor Circuit (Passenger Side)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code B1421

This diagnostic trouble code (DTC) is a generic code. Fault B1421 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code B1421 – solar sensor circuit (passenger side)

The sunshine sensor is mounted on top of the dashboard. Its function is to detect sunlight to control the AUTO mode of the air conditioning system.

The output voltage of this sensor varies according to the amount of sunlight hitting it. If the illumination increases, the output voltage increases accordingly; if the light decreases, the output voltage decreases.

The air conditioner amplifier detects all these voltage changes, to control the automatic mode of maintaining the temperature in the vehicle interior. DTC code B1421 OBDII is set because a fault is detected in the passenger side sunlight sensor circuit.

Symptoms of vehicle malfunctions

The main signal that an error B1421 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Most likely, there will be no symptoms, except for the stored fault code and illumination of the “Check engine” lamp on the instrument panel.

The fault B1421 is not a serious error, as it does not directly affect the safety of driving. At this error, automatic air conditioning system may work incorrectly, or not work at all.

Factors that can cause this error code

The error code B1421 can mean that one or more of the following problems have occurred:

  • The solar sensor may be faulty.
  • The solar sensor wiring harness is open or shorted.
  • The solar sensor circuit may have a bad connection, resulting in a short or open circuit.
  • Faulty air conditioning system amplifier.

How to fix or reset OBD-2 code B1421

Some suggested steps for troubleshooting and fix the error code B1421:

  1. Examine the maintenance bulletins (TSB). For known problems with your particular vehicle.
  2. Check the solar sensor circuit wiring for damage. If defects caused by wear or corrosion are found, make appropriate repairs.
  3. Measure the Solar Sensor wiring voltage to make sure it is not open or short-circuited. If the actual voltages differ from those indicated, make corrections.
  4. Inspect the solar sensor and air conditioner amplifier for damage. Follow the manufacturer’s recommendations to check their integrity.
  5. If damage is found to any of these components, make the necessary repairs.

Diagnose and repair of problems

The first step in the B1421 troubleshooting process is to review the Technical Service Bulletins (TSB). For known problems with a particular vehicle.

The advanced diagnostic steps are very vehicle specific. It may require, special equipment and knowledge to accurately perform the steps.

Next, wires, connectors and other electrical components of the system should be checked. If you find any defects, eliminate them. After that, you need to clear the error codes from the PCM memory again and recheck the system.

If the error code appears again, check the solar sensor itself and the air conditioner booster for damage, and if necessary, make the necessary replacements. In most cases, these actions will solve the problem B1421 which appeared on your car.

On which vehicles does this problem occur most frequently

Fault code B1421 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Lexus
  • Mitsubishi
  • Toyota (Camry, RAV4)

Fault code B1421 can sometimes be found with other errors. The most common are the following: B1424, B14A1.


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