P1812 DTC Code: Causes, Symptoms, and Solutions


In the world of automobiles, DTC codes are an essential diagnostic tool used to identify specific issues with a vehicle. One common DTC code that many car owners encounter is the P1812 code. In this article, we will dive deep into the intricacies of the P1812 DTC code, including its causes, symptoms, and possible solutions. So, if you’re a car owner, mechanic, or simply someone interested in learning more about automotive diagnostics, keep reading!

What is the P1812 DTC Code?

The P1812 DTC code stands for “Transmission 4-Wheel Drive Mode Select Circuit Failure.” It indicates that there is a problem with the circuit responsible for selecting the 4-wheel drive mode in your vehicle’s transmission system. This code is commonly found in vehicles equipped with 4-wheel drive or all-wheel drive capabilities.

Common Causes of the P1812 DTC Code

There can be several underlying causes behind the P1812 DTC code. Let’s explore some of the most common ones:

  1. Faulty Mode Select Switch: A malfunctioning mode select switch can trigger the P1812 code. The switch might not be able to properly communicate with the transmission, resulting in a circuit failure.

  2. Electrical Issues: Problems with the wiring, connectors, or other electrical components involved in the 4-wheel drive mode select circuit can lead to the P1812 DTC code. Loose connections or damaged wires can interrupt the flow of signals, causing the circuit to fail.

  3. Software or Control Module Malfunction: In some cases, the P1812 code can be a result of issues with the vehicle’s software or control module. Corrupted software or a faulty control module can prevent the proper operation of the 4-wheel drive mode select circuit.

Symptoms of a P1812 DTC Code

When the P1812 DTC code is present, you may experience one or more of the following symptoms:

  1. Illuminated Malfunction Indicator Lamp (MIL): The MIL, also known as the “Check Engine Light,” will likely illuminate on your vehicle’s dashboard when the P1812 code is detected. This serves as an early warning indication that there is an issue with your transmission’s 4-wheel drive mode select circuit.

  2. Inability to Change Drive Mode: If the P1812 DTC code is triggered, you may find that your vehicle is stuck in one specific drive mode and cannot switch to another. This can be particularly problematic if you frequently need to alternate between different driving modes based on the road conditions.

  3. Strange Transmission Behavior: Another common symptom associated with the P1812 code is unusual transmission behavior. This can include rough shifting, delayed engagement, or even complete transmission failure in severe cases. These abnormal behaviors can be a result of the circuit failure affecting the transmission’s ability to function properly.

How to Diagnose and Fix a P1812 DTC Code

Diagnosing and fixing a P1812 DTC code usually involves the following steps:

  1. Use an OBD-II Scanner: To begin the diagnosis process, connect an OBD-II scanner to your vehicle’s diagnostic port. This will allow you to retrieve the fault codes stored in the vehicle’s computer system, including the P1812 code.

  2. Inspect the Mode Select Switch: Start by examining the mode select switch for any signs of damage or loose connections. If any issues are found, replace the switch or repair the wiring as necessary.

  3. Check the Circuit Connections: Inspect the wiring harness, connectors, and other electrical components associated with the 4-wheel drive mode select circuit. Ensure that all connections are secure and free from corrosion or damage. Repair or replace any faulty components as required.

  4. Test the Control Module: If the issue persists, it might be necessary to test or replace the control module responsible for the 4-wheel drive mode selection. This requires specialized diagnostic tools and technical expertise, so consulting a professional mechanic is advisable.

  5. Clear the Codes and Test Drive: After making any repairs or replacements, clear the fault codes from the vehicle’s computer system using the OBD-II scanner. Take the vehicle for a test drive to ensure that the P1812 code no longer appears and that the transmission is functioning correctly.

Frequently Asked Questions (FAQs)

1. Can I continue driving my vehicle with a P1812 DTC code?

Driving with a P1812 DTC code is not recommended. While the severity of the issue may vary, it is crucial to address the problem promptly to prevent further damage to your vehicle’s transmission system.

2. How much does it cost to fix a P1812 DTC code?

The cost of fixing a P1812 DTC code can vary depending on the underlying cause and the specific vehicle model. It is recommended to consult a professional mechanic for an accurate diagnosis and cost estimate.

3. Can a P1812 DTC code be prevented?

Preventing the P1812 DTC code involves regular maintenance of your vehicle’s transmission system. Ensure that the mode select switch, wiring, and connectors are inspected periodically to catch any potential issues before they escalate.

In conclusion, the P1812 DTC code indicates a failure in the transmission 4-wheel drive mode select circuit. Understanding its causes, symptoms, and potential solutions can help you address the issue effectively. Remember to consult a professional mechanic for a thorough diagnosis and repair to ensure the proper functioning of your vehicle’s transmission system.

About author


Meet Sam Mitchell, your experienced and reliable guide in the complex world of car fault codes. With a robust career spanning over 15 years as a professional car mechanic, John has the skills, knowledge, and practical experience to help you navigate car fault issues with confidence.


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