AutoCodes – Generic – P1838

P1838 Code - Internal Mode Switch 'A' Circuit High Voltage

Quick Answer

The internal mode switch indicates the Transmission Control Module (TCM) which gear position the vehicle operator has selected. Common causes include Faulty Transmission Internal Mode Switch, Transmission Internal Mode Switch harness is open or shorted, Transmission 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: P1838 indicates Internal Mode Switch 'A' Circuit High Voltage.
Common causes: Common causes include Faulty Transmission Internal Mode Switch, Transmission Internal Mode Switch harness is open or shorted, Transmission 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 15,925

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 23, 2024

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1838 Description

The internal mode switch indicates the Transmission Control Module (TCM) which gear position the vehicle operator has selected. The internal mode switch consists of 5 separate hall effect switches. Each hall effect switch is supplied with a 9 V reference circuit and a signal circuit from the TCM. Each signal circuit for each gear selector position will have either a voltage reading of 0.70–0.96 V indicating On or 1.68–2.38 V indicating Off. The voltage values on each internal mode switch circuit will change and are dependent on the position of the gear selector. The state of each internal mode switch A/B/C/P/S signal circuit is displayed on the scan tool. The Diagnostic Trouble Code (DTC) will be set when the TCM has detected the internal mode switch A signal circuit voltage is greater than 2.38 V, for 1.75 s.

OBDII Code P1838 - Internal Mode Switch 'A' Circuit High Voltage - AutoCodes.com — P1838 Code - Internal Mode Switch 'A' Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P1838?

Faulty Transmission Internal Mode Switch
Transmission Internal Mode Switch harness is open or shorted
Transmission Internal Mode Switch circuit poor electrical connection
Faulty Transmission Control Module (TCM)

How to Fix the DTC P1838?

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 P1838 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.

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Need Help with the Code?

Get the P1838 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P1838 Buick — Internal Mode Switch 'A' Circuit High Voltage
P1838 Cadillac — Internal Mode Switch 'A' Circuit High Voltage
P1838 Chevrolet — Internal Mode Switch 'A' Circuit High Voltage
P1838 Ford — Transmission Transfer Case Shift Motor Circuit Failure
P1838 GMC — Internal Mode Switch 'A' Circuit High Voltage
P1838 Lincoln — Transmission Transfer Case Shift Motor Circuit Failure
P1838 Mercury — Transmission Transfer Case Shift Motor Circuit Failure

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 P1838 Code

1. What are the common symptoms of OBDII code P1838 (Internal Mode Switch 'A' Circuit High Voltage)?

- Common symptoms include issues with shifting gears, erratic transmission behavior, and illuminated warning lights on the dashboard.

2. What are the possible causes of OBDII code P1838?

- The code P1838 can be caused by a faulty internal mode switch, damaged wiring or connectors in the circuit, or issues with the transmission control module.

3. How can I diagnose the root cause of OBDII code P1838?

- To diagnose the issue, it is recommended to perform a thorough inspection of the internal mode switch, check the circuit for any damaged wiring or connectors, and use a diagnostic scanner to read the trouble codes stored in the system.

4. Can I continue driving my vehicle with OBDII code P1838?

- It is not recommended to continue driving the vehicle with OBDII code P1838, as it can lead to further damage to the transmission system. It is best to address the issue promptly.

5. How can I repair OBDII code P1838?

- Repairing OBDII code P1838 may involve replacing the internal mode switch, repairing or replacing damaged wiring or connectors, or reprogramming the transmission control module. It is advisable to consult a professional mechanic for proper diagnosis and repair.

6. Are there any DIY tips for fixing OBDII code P1838?

- While some basic troubleshooting steps can be done at home, such as checking for loose connections and inspecting wiring for damage, it is generally recommended to seek the expertise of a qualified mechanic for accurate diagnosis and repair.

7. Can a low battery voltage trigger OBDII code P1838?

- Yes, low battery voltage or a weak electrical system can sometimes cause erratic behavior in the transmission system, leading to the triggering of OBDII code P1838. Ensuring a healthy battery and electrical system can help prevent such issues.

8. Is it necessary to reset the trouble codes after repairing OBDII code P1838?

- Yes, it is recommended to clear the trouble codes using a diagnostic scanner after repairing OBDII code P1838. This will reset the system and allow you to monitor if the issue has been successfully resolved.

9. How much does it typically cost to repair OBDII code P1838 at a mechanic's shop?

- The cost of repairing OBDII code P1838 can vary depending on the extent of the issue, the labor rates of the mechanic, and the cost of any replacement parts needed. It is best to obtain quotes from different shops for an accurate estimate.

10. Can regular maintenance help prevent OBDII code P1838 from occurring?

- Regular maintenance, such as checking and replacing transmission fluid as recommended, inspecting wiring harnesses for damage, and keeping the vehicle's electrical system in good condition, can help reduce the chances of OBDII code P1838 occurring.