AutoCodes – GMC – P1820 GMC

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

Quick Answer

With the engine runtime over 5 seconds, system voltage from 8-18v, Fuel Cutoff inactive, engine torque from 30-148 ft-lb (40-200 Nm), the Powertrain Control Module (PCM) detects that the Internal Mode Switch (IMS) signal indicated PARK for 2 seconds and then the IMS indicated a transitional state between D4 and D3, conditions met for 5 seconds. Common causes include Faulty Internal Mode Switch, Internal Mode Switch harness is open or shorted, Internal Mode Switch circuit poor electrical connection. 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, Internal Mode Switch harness is open or shorted, Internal Mode Switch circuit poor electrical connection.
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.

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Code Popularity 2,122

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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Table of contents Created and updated by William Orellana on Sep 21, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1820 GMC Description

OBDII Code P1820 GMC - Internal Mode Switch Circuit 'A' Low - AutoCodes.com — P1820 GMC Code - Internal Mode Switch Circuit 'A' Low

What does this mean?

What are the Possible Causes of the DTC P1820 GMC?

Faulty Internal Mode Switch
Internal Mode Switch harness is open or shorted
Internal Mode Switch circuit poor electrical connection

How to Fix the DTC P1820 GMC?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1820 GMC code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P1820 GMC code?

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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.