P1840 GMC Code - Internal Mode Switch 'S' Circuit Low Voltage
Quick Answer
The P1840 GMC diagnostic trouble code (DTC) refers to an issue with the Internal Mode Switch 'S' Circuit Low Voltage. Common causes include Faulty Internal Mode Switch (IMS), Damaged wiring or connectors in the IMS circuit, Corrosion or poor electrical connections in the 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
- P1840 GMC indicates Internal Mode Switch 'S' Circuit Low Voltage.
- Common causes
- Common causes include Faulty Internal Mode Switch (IMS), Damaged wiring or connectors in the IMS circuit, Corrosion or poor electrical connections in the 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.
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Code P1840 GMC Description
The P1840 GMC diagnostic trouble code (DTC) refers to an issue with the Internal Mode Switch 'S' Circuit Low Voltage. This code indicates that there is a problem with the circuit responsible for transmitting signals related to the gear shift position to the vehicle's engine control module (ECM). The Internal Mode Switch (IMS) is a component that detects the gear position (Park, Reverse, Neutral, Drive, etc.) selected by the driver and communicates this information to the ECM. When the voltage in the circuit is lower than the specified threshold, the P1840 code is triggered.
Common Causes of P1840 GMC
- Faulty Internal Mode Switch (IMS)
- Damaged wiring or connectors in the IMS circuit
- Corrosion or poor electrical connections in the circuit
- Issues with the ECM or transmission control module (TCM)
- Software glitches or calibration errors
Symptoms of P1840 GMC
- Incorrect gear display on the instrument cluster
- Harsh shifting or erratic transmission behavior
- Engine stalling when shifting gears
- Reduced fuel efficiency
- Illumination of the Check Engine Light
How to Fix P1840 GMC
- Begin by conducting a thorough inspection of the IMS circuit, including wiring, connectors, and the switch itself.
- Test the voltage output of the IMS to determine if it falls below the specified threshold.
- Replace the Internal Mode Switch if it is found to be faulty.
- Repair or replace any damaged wiring or connectors in the circuit.
- Clear the DTC and perform a test drive to ensure the issue has been resolved.
Cost to Fix P1840 GMC
The typical repair costs for addressing the P1840 GMC code can vary depending on the specific cause of the issue. In general, replacing the Internal Mode Switch and addressing any wiring or connector issues can range from $200 to $500, including parts and labor. However, it's essential to note that diagnosis time and labor rates at auto repair shops can vary significantly. Rates typically range between $80 and $150 per hour, but may be higher in metropolitan areas or at dealerships, and lower at independent shops. For a more accurate estimate, it is advisable to consult with local auto repair shops.
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Information for Specific GMC Models
- P1840 2014 GMC Sierra — Internal Mode Switch 'S' Circuit Low Voltage
- P1840 2015 GMC Sierra — Internal Mode Switch 'S' Circuit Low Voltage
- P1840 2016 GMC Sierra — Internal Mode Switch 'S' Circuit Low Voltage
- P1840 2017 GMC Sierra — Internal Mode Switch 'S' Circuit Low Voltage
- P1840 2018 GMC Sierra — Internal Mode Switch 'S' Circuit Low Voltage
Frequently Asked Questions about P1840 GMC Code
1. What are common symptoms of OBDII code P1840 GMC (Internal Mode Switch 'S' Circuit Low Voltage)?
- Common symptoms include issues with shifting gears, hesitation or jerking during acceleration, and the inability to shift out of park.
2. What are the possible causes of OBDII code P1840 GMC?
- The code may be triggered due to a faulty internal mode switch, damaged wiring or connectors, a defective transmission range sensor, or a problem with the transmission control module.
3. How can I diagnose the cause of OBDII code P1840 GMC?
- Diagnostic steps may include checking the internal mode switch for proper operation, inspecting wiring and connectors for damage, testing the transmission range sensor, and scanning the transmission control module for other related error codes.
4. Can I continue driving my vehicle with OBDII code P1840 GMC?
- It is not recommended to continue driving the vehicle with this code present, as it can lead to further transmission issues and potential safety hazards.
5. How can I repair OBDII code P1840 GMC?
- Repair options may include replacing the internal mode switch, repairing or replacing damaged wiring/connectors, replacing the transmission range sensor, or reprogramming the transmission control module.
6. Is it possible to clear OBDII code P1840 GMC without fixing the underlying issue?
- Clearing the code without addressing the root cause will likely result in the code reappearing once the issue is detected again during vehicle operation.
7. Are there any DIY fixes for OBDII code P1840 GMC?
- DIY fixes may be limited due to the complexity of the transmission system, but basic checks like inspecting wiring connections and ensuring the internal mode switch is functioning properly can be done by experienced DIYers.
8. How much does it typically cost to repair OBDII code P1840 GMC at a repair shop?
- Repair costs can vary depending on the specific cause of the code, but expect to pay anywhere from $200 to $500 for parts and labor at a repair shop.
9. Can a mechanic reset OBDII code P1840 GMC without making any repairs?
- While a mechanic can clear the code from the system, it is important to address the underlying issue to prevent further problems with the transmission.
10. How long does it take to repair OBDII code P1840 GMC?
- The repair time can vary based on the exact cause of the code and the availability of parts, but most repairs related to this code can typically be completed within a few hours to a day at a repair shop.
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