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Engine-Codes – GMC – P1820 GMC

P1820 GMC Code - Internal Mode Switch Circuit 'A' Low

Quick Answer

The P1820 code for GMC vehicles refers to an issue with the Internal Mode Switch Circuit 'A' being detected as low. Common causes include Faulty Internal Mode Switch, Damaged wiring or connectors in the IMS circuit, Corrosion or contamination in the IMS circuit. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P1820 GMC indicates Internal Mode Switch Circuit 'A' Low.
Common causes
Common causes include Faulty Internal Mode Switch, Damaged wiring or connectors in the IMS circuit, Corrosion or contamination in the IMS circuit.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 08, 2024
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Code P1820 GMC Description

The P1820 code for GMC vehicles refers to an issue with the Internal Mode Switch Circuit 'A' being detected as low. The Internal Mode Switch (IMS) is a component of the transmission system that communicates the gear selector position to the Powertrain Control Module (PCM). When the PCM receives a signal indicating that the IMS circuit 'A' is low, it means that there is a problem with the voltage levels in that particular circuit. This can lead to incorrect gear selection, transmission shifting issues, and potential safety hazards while driving.

OBDII Code P1820 GMC - Internal Mode Switch Circuit 'A' Low
P1820 GMC Code - Internal Mode Switch Circuit 'A' Low

Common Causes of P1820 GMC

  1. Faulty Internal Mode Switch
  2. Damaged wiring or connectors in the IMS circuit
  3. Corrosion or contamination in the IMS circuit
  4. Issues with the PCM or transmission control module
  5. Electrical problems such as short circuits or open circuits

Symptoms of P1820 GMC

  1. Incorrect gear selection on the dashboard display
  2. Delayed or harsh shifting of gears
  3. Transmission slipping or jerking during acceleration
  4. Loss of power or acceleration issues
  5. Illumination of the check engine light

How to Fix P1820 GMC

  1. Begin by diagnosing the specific cause of the P1820 code by using a scan tool to read the fault codes and perform a thorough inspection of the IMS circuit.
  2. Check the wiring and connectors for any damage, corrosion, or loose connections. Repair or replace any faulty components as needed.
  3. Test the Internal Mode Switch itself to ensure it is functioning correctly. Replace the IMS if it is found to be defective.
  4. Clear the fault codes from the PCM memory and reset the system to see if the issue has been resolved.
  5. Test drive the vehicle to confirm that the transmission is shifting smoothly and that the code does not reappear.

Cost to Fix P1820 GMC

The cost of repairing a P1820 code for GMC vehicles can vary depending on the specific cause of the issue and the extent of the repairs needed. On average, the cost of replacing an Internal Mode Switch or repairing wiring issues related to this code can range from $200 to $500, including parts and labor. However, it is essential to note that the actual cost may differ based on factors such as the location of the repair shop, the vehicle's make and model, and the technician's hourly labor rates. It is recommended to obtain a detailed quote from a reputable auto repair shop to determine the exact cost of addressing this issue for your specific vehicle.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P1820 GMC Code

1. What are the common symptoms of OBDII code P1820 GMC (Internal Mode Switch Circuit 'A' Low)?

Symptoms may include issues shifting gears, the transmission not entering the correct gear, and the vehicle going into "limp mode."

2. What can cause the OBDII code P1820 GMC to trigger?

Common causes include a faulty internal mode switch, damaged wiring or connectors in the circuit, or a problem with the transmission control module.

3. How serious is the OBDII code P1820 GMC?

This code can lead to drivability issues and potential safety concerns if not addressed promptly. It is recommended to address this issue as soon as possible.

4. Can I continue driving with the OBDII code P1820 GMC present?

It is not recommended to continue driving with this code present, as it can cause further damage to the transmission and other related components.

5. How is the OBDII code P1820 GMC diagnosed?

Diagnosis typically involves using a scan tool to read the code, checking the internal mode switch for proper operation, and inspecting the wiring and connectors for any damage.

6. What are some repair tips for fixing the OBDII code P1820 GMC?

Repair tips may include replacing the internal mode switch, repairing any damaged wiring or connectors, and ensuring proper connection to the transmission control module.

7. Can I fix the OBDII code P1820 GMC myself?

While some DIY enthusiasts may attempt to address this issue, it is recommended to seek professional help, especially when dealing with transmission-related problems.

8. How much does it cost to repair the OBDII code P1820 GMC?

The cost of repairs can vary depending on the extent of the issue, the parts needed, and the labor rates of the repair shop. It is advisable to get a few quotes from different mechanics.

9. How long does it take to fix the OBDII code P1820 GMC?

The repair time can vary depending on the exact cause of the issue and the expertise of the technician. In some cases, the repair can be completed within a few hours.

10. How can I prevent the OBDII code P1820 GMC from reoccurring?

Regular maintenance of the transmission system, including checking for any signs of wear or damage, can help prevent this code from reoccurring. It is also essential to address any related issues promptly.

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