P0642 OBD-II Trouble Code: Sensor Reference Voltage “A” Circuit Low

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0642 code

P0642 is a diagnostic trouble code (DTC) for "Sensor Reference Voltage “A” Circuit Low". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0642 DIAGNOSTIC Get a fair and transparent estimate upfront

P0642 code definition

The P0642 code indicates that the sensor reference voltage “A” circuit is too low compared to the manufacturer’s specifications, as detected by the powertrain control module, or PCM.

What the P0642 code means

The PCM or one of the supporting control modules has detected that there is a voltage reading that is too low in a particular area of the circuit related to one of many vehicle components, including climate control, proximity alert, traction control, turbo control, cruise control, anti-theft features, fuel injection control, antilock brake control, and others.

What causes the P0642 code?

Most of the time, the P0642 code is caused by shorted or open wiring or connectors between the supporting control modules, or from the control modules to the PCM. Other causes may include:

  • Faulty engine control module (ECM)
  • Open or shorted electrical components from the engine sensors
  • Open or shorted ECM harness
  • Shorted sensor on 5-volt circuit
  • Loose or disconnected ground wires in the PCM input circuitry
  • Internal malfunctions in the PCM

What are the symptoms of the P0642 code?

In addition to the presence of the P0642 code in the PCM memory, the vehicle may not be able to start. Starting may be difficult, and the engine may run roughly. Fuel efficiently may decrease, the engine may misfire, and the driver may notice an overall decrease in engine power. The Check Engine Light will be illuminated, but it may take several drive cycles to do so.

How does a mechanic diagnose the P0642 code?

After an OBD-II scanner verifies the P0642 code, a technician should visually inspect all the wiring, connectors, and other components related to the PCM and the supporting control modules. Any damaged elements should be replaced, reconnected, or repaired as necessary. The technician should clear the code from the PCM after ensuring that all electrical components are working properly, and perform a test drive. If the code returns, the issue requires more in-depth repair.

Common mistakes when diagnosing the P0642 code

In many cases when the issue is related to communication between control modules, other codes will appear in the PCM. These are typically a result of the faulty connection causing the P0642 code, and do not actually require repair. However, it is common for these issues to be diagnosed and repaired first, which does not solve the underlying issue.

How serious is the P0642 code?

If an OBD-II scanner detects the P0642 code, it is important to have the vehicle inspected and repaired right away. A miscommunication between control modules will affect the drivability of the vehicle, and decrease the overall engine performance. In order to ensure that the vehicle remains operational, it’s important to address the issue causing the P0642 code right away.

What repairs can fix the P0642 code?

In many cases, the cause of the P0642 code will be repaired during the initial diagnosis, because the electrical components are the most likely issue when this code is stored. However, there are other repairs that may need to be made to solve the root issue present. These include:

  • Replacing faulty engine control module (ECM).
  • Replacing or repairing open or shorted ECM harness.
  • Replacing shorted sensor on 5-volt circuit.
  • Replacing a PCM that shows signs of internal malfunctions.
  • Replacing any control modules that are malfunctioning.

When replacing any control modules, the new modules will have to be reprogrammed. If the mechanic skips this step, it is likely that many codes will be stored over the next few drive cycles. A PCM that is not properly programmed can make the vehicle enter a no start condition.

It is also important that the P0642 code be cleared and the system be retested after every possible repair. This process narrows down the root cause of the issue until the correct repair is found and performed.

Need help with a P0642 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
P0642
Check Engine Light

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0642 code.

SCHEDULE P0642 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating

(6,144)

Rating Summary
5,685
221
51
35
152
5,685
221
51
35
152

Chris

11 years of experience
13 reviews
Chris
11 years of experience
Ford F-150 - Check Engine Light is on - North Salt Lake, Utah
We were having problems with our check engine light, and Chris was exceptionally thorough until he found the problem and could help resolve the situation. We appreciate having someone who cares enough to get the job done right, not just done. We will definitely use Chris' services in the future. Thanks Chris.

Leng

21 years of experience
2 reviews
Leng
21 years of experience
Mazda MPV - Check Engine Light is on - Seattle, Washington
Leng arrived on time and explained the issue that my van is having. I will make a follow up appointment for the fix. Friendly, easy to talk to, and professional - thank you very much!

Okela

13 years of experience
11 reviews
Okela
13 years of experience
Land Rover LR4 - Check Engine Light is on - Brooklyn, New York
Okela was incredible! He is super thorough and took time to walk us through the issues with our LR4. Couldn’t recommend more! Thank you Okela!!

Robert

37 years of experience
188 reviews
Robert
37 years of experience
Land Rover LR2 - Check Engine Light is on - Atlanta, Georgia
Robert arrived on time. Did a diagnostic check quickly. He was friendly, and gave great service. He knows how to work on a Land Rover.


Related questions

Whats wrong , engine codes p0605,p0842,p0642, and p0401 thrown twice , light front end damage wothout airbag deployment

Hello, thank you for writing in. If the vehicle was in a wreck, the issues are likely independent from each other. One issue seems to be a powertrain control module electrical malfunction. This could be an issue with an input...

More related articles

P0538 OBD-II Trouble Code: A/C Evaporator Temperature Sensor Circuit High
P0538 means that voltage readings from the A/C evaporator temperature sensor that are irregular due to a faulty temperature sensor or wiring.
P2779 OBD-II Trouble Code: Downshift Switch Circuit Range/Performance
P2779 means a problem with the downshift switch circuit usually caused by liquid that has spilled on the switch or other electrical issues.
P0921 OBD-II Trouble Code: Gear Shift Forward Actuator Circuit Range/Performance
P0921 means there is a problem with the gear shift forward actuator circuit, likely due to a faulty actuator or bad wiring.

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com