AutoCodes – Buick – P0642 Buick

P0642 Buick Code - 5 Volt Reference 1 Circuit Low 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: P0642 Buick indicates 5 Volt Reference 1 Circuit Low 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 2,032

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 P0642 Buick 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 lower than the expected voltage on any of the 5 Volt reference circuits for greater than 0.5 s.

OBDII Code P0642 Buick - 5 Volt Reference 1 Circuit Low Voltage - AutoCodes.com — P0642 Buick Code - 5 Volt Reference 1 Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P0642 Buick?

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 P0642 Buick?

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 P0642 Buick 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?

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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 P0642 Buick Code

1. What are the common symptoms of OBDII code P0642 in a Buick?

- Common symptoms include poor engine performance, rough idling, stalling, and potential issues with electronic components like the fuel pump or sensors.

2. What does the OBDII code P0642 "5 Volt Reference 1 Circuit Low Voltage" mean for a Buick?

- This code indicates that the power supply voltage to one of the sensors or components in the 5-volt reference circuit is lower than the expected range.

3. What are the possible causes of OBDII code P0642 in a Buick?

- Possible causes include a faulty sensor, damaged wiring in the 5-volt reference circuit, a short circuit, or a problem with the Engine Control Module (ECM).

4. How can I diagnose the OBDII code P0642 in my Buick?

- Diagnosis typically involves inspecting the wiring and connectors in the 5-volt reference circuit, testing the sensors, checking for shorts or open circuits, and using a multimeter to measure voltage.

5. Can I continue driving my Buick with the OBDII code P0642 present?

- It is not recommended to drive your Buick with this code present, as it can lead to further damage to the engine or other components. It's best to address the issue promptly.

6. How can I repair OBDII code P0642 in my Buick?

- Repair methods may include replacing the faulty sensor, repairing damaged wiring, addressing any short circuits, or reprogramming the ECM if necessary.

7. Is it safe to clear the OBDII code P0642 in my Buick with a diagnostic tool?

- Clearing the code with a diagnostic tool may temporarily turn off the check engine light, but it is important to address the underlying issue causing the code to prevent further problems.

8. Can extreme weather conditions affect the occurrence of OBDII code P0642 in a Buick?

- Yes, extreme temperatures can sometimes cause issues with the 5-volt reference circuit, leading to the triggering of code P0642. Insulating wiring or using proper shielding may help prevent this.

9. How do I prevent OBDII code P0642 from recurring in my Buick?

- Regular maintenance, checking for loose connections, ensuring proper grounding, and using quality sensors can help prevent the recurrence of code P0642 in your Buick.

10. Will OBDII code P0642 cause my Buick to fail an emissions test?

- Yes, if the code is not addressed and the vehicle's emissions control system is affected, it may lead to a failed emissions test. It's important to resolve the issue before undergoing emissions testing.