AutoCodes – GMC – P0643 2018 GMC Sierra

P0643 2018 GMC Sierra Code - 5 Volt Reference 1 Circuit High Voltage

Quick Answer

The Engine Control Module (ECM) has four (4) internal 5 Volt reference circuits (Some models have two (2) internal 5 Volt reference circuits). Common causes include Faulty Sensor on 5 Volt circuit, Sensor on 5 Volt circuit harness is open or shorted, Sensor on 5 Volt 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: P0643 2018 GMC Sierra indicates 5 Volt Reference 1 Circuit High Voltage.
Common causes: Common causes include Faulty Sensor on 5 Volt circuit, Sensor on 5 Volt circuit harness is open or shorted, Sensor on 5 Volt 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 229

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 Jul 17, 2022

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0643 2018 GMC Sierra Description

The Engine Control Module (ECM) has four (4) internal 5 Volt reference circuits (Some models have two (2) internal 5 Volt reference circuits). Each internal reference circuit provides external 5 Volt reference circuits for more than one sensor. A short to ground or short to voltage on one external 5 Volt reference circuit can affect all the components connected to the same internal 5 Volt reference circuit. The Diagnostic Trouble Code (DTC) will be set when the ECM detects a higher than the expected voltage on any of the 5 Volt reference circuits for greater than 0.5 s.

OBDII Code P0643 2018 GMC Sierra - 5 Volt Reference 1 Circuit High Voltage - AutoCodes.com — P0643 2018 GMC Sierra Code - 5 Volt Reference 1 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0643 2018 GMC Sierra?

Faulty Sensor on 5 Volt circuit
Sensor on 5 Volt circuit harness is open or shorted
Sensor on 5 Volt circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P0643 2018 GMC Sierra?

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 does this mean?

Code Tech Notes

Disconnecting one component at a time from the affected 5 Volt reference circuit while observing the scan tool 5 Volt Reference Circuit Status parameter may help locate the fault. The scan tool parameter will change from Malfunction to OK when the source of the fault is disconnected. If all 5 Volt reference components have been disconnected and a fault is still indicated, the fault may exist in the wiring harness.

The 5 Volt reference 1 circuit provides 5 Volt to the following sensors: (Some models may have different sensors, please consult the factory service manual for the list of sensors for your model and year)

- Air conditioning (A/C) refrigerant pressure sensor
- Camshaft position sensor
- Engine oil pressure sensor
- Fuel pressure sensor
- Fuel rail pressure sensor
- Fuel tank pressure sensor
- Multifunction intake air sensor

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0643 2018 GMC Sierra 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 P0643 2018 GMC Sierra 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 P0643 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P0643 in a 2018 GMC Sierra?

- Common symptoms include issues with the vehicle's electrical system, such as erratic gauge readings, malfunctioning sensors, or dashboard warning lights.

2. What causes the OBDII code P0643 (5 Volt Reference 1 Circuit High Voltage) in a 2018 GMC Sierra?

- The code is typically triggered by a high voltage condition in the 5-volt reference circuit, often caused by a short circuit, damaged wiring, or a faulty sensor.

3. How can I diagnose the OBDII code P0643 in my 2018 GMC Sierra?

- To diagnose the issue, you can use a scan tool to read the trouble code, inspect the wiring for any visible damage, and test the sensors connected to the 5-volt reference circuit.

4. Is it safe to continue driving my 2018 GMC Sierra with OBDII code P0643 active?

- It is not recommended to continue driving the vehicle with an active P0643 code, as it can lead to further electrical problems and potential damage to other components.

5. How can I repair OBDII code P0643 in a 2018 GMC Sierra?

- Repairing the P0643 code involves identifying and fixing the underlying cause, which may include repairing or replacing damaged wiring, sensors, or connectors in the 5-volt reference circuit.

6. Can a DIY enthusiast fix the OBDII code P0643 issue in a 2018 GMC Sierra?

- While some DIY enthusiasts may have the skills to diagnose and repair the issue causing the P0643 code, it is recommended to consult a professional mechanic for accurate diagnosis and repair.

7. Are there any recalls or technical service bulletins related to OBDII code P0643 in 2018 GMC Sierra vehicles?

- It is advisable to check with the manufacturer or authorized dealerships for any recalls or technical service bulletins related to the P0643 trouble code in the 2018 GMC Sierra.

8. Will resetting the OBDII code P0643 in my 2018 GMC Sierra make it go away permanently?

- Simply resetting the code may temporarily clear the warning light, but if the underlying issue causing the P0643 code is not addressed, it is likely to reappear.

9. How much can I expect to pay for professional repairs for OBDII code P0643 in a 2018 GMC Sierra?

- The cost of repairs for the P0643 code can vary depending on the extent of the damage and the specific components needing replacement, but it is advisable to budget for diagnostic fees and parts/labour costs.

10. Can a faulty battery or alternator cause OBDII code P0643 to appear in a 2018 GMC Sierra?

- Yes, a faulty battery or alternator can sometimes cause voltage irregularities that trigger the P0643 code, so it's essential to check these components during diagnosis.