Need any ideas 2018 Sierra 6.2.

Brett Boyd · December 29, 2021

This past Friday morning went and started my truck to get warm came back about 5-10 minutes later with the truck off lights still on and it’s throwing engine reduced power and p0641 code. Truck won’t turn over at all. Any ideas or tips? Thank you in advance

Edited December 29, 2021 by Brett Boyd
Added tags

Brett Boyd · December 29, 2021

Bump

JimCost2014 · December 30, 2021

56 minutes ago, Brett Boyd said:

Bump

Could be a few different things:

What Does the P0641 Code Mean?

Diagnostic trouble code (DTC) P0641 stands for “Sensor Reference Voltage “A” Circuit/Open.” It is logged whenever the PCM detects voltage that does not match manufacturer specifications on the 5-volt reference circuit.

If the 5 volts feeding the three-wire sensors is shorted to ground, it pulls all the three-wire sensor voltages to zero, and on some vehicles (like Fords), it will put the PCM to sleep so that there is no spark, fuel injection, or communication with the scan tool; thus there is no DTC for a shorted 5 volt rail on a system where the ECM/PCM has just one 5 volt rail because the ECM/PCM can’t communicate anyway.

If, however, there are multiple 5 volt rails, a short on just one of the rails won’t disable the engine. On a Ford, if any three-wire sensor shorts out, it kills the whole system. On a system with multiple rails, only one system goes down, but the engine will still run, albeit in limp mode (usually).

A 2016 Chevy Silverado, for example, has five different 5 volt rails. A short on any of these five rails will cause a different code to be set for each rail. The 5 volt rails on the Silverado each feed a different set of sensors.

Electric transmission control module designed for automatic transmission

P0641 code is logged whenever the PCM detects voltage that does not match manufacturer specifications on the 5-volt reference circuit.

Rail 1 feeds the Engine Oil Pressure Sensor, the Fuel Rail Pressure Sensor, the A/C refrigerant pressure sensor, the Exhaust Pressure Differential sensor, the Camshaft Position Sensor. A short on this rail will set code P0641.

The other four 5 volt rails set different codes.

Rail 2 feeds Accelerator Pedal Sensor 2, the MAP sensor, and the Brake Pedal Position Sensor. That rail will set a P0651 if it shorts out.

Rail 3 feeds Accelerator Pedal Sensor 1 and the Intake Air Valve Position Sensor. That rail sets a DTC P0697.

Rail 4 feeds the EGR position sensor. That rail sets a DTC DTC P06A3.

Rail 5 feeds the Crank Position Sensor, The Cooling Fan Speed Sensor, the DEF fluid pressure sensor, and the Turbocharger Vane Position Sensor. That rail sets a DTC P06D2.

For an advanced, technical discussion of two-wire vs three-wire sensors and reference voltage, you can read our explanation here.

Note: The definition of code P0641 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Possible Causes of the P0641 Code?

engine control unit or ECU of a car with multicolored wires plug at foreground

Wiring or connection issues can cause the P0641 code.

The code P0641 can be triggered by various issues, including:

Malfunctioning sensor
Wiring or connection issues
PCM problems

What are the Common Symptoms of the P0641 Code?

Keep an eye out for these warning signs if you are dealing with a P0641 code:

Check Engine Light is illuminated
Sensor-related performance issues

How to Diagnose the P0641 Code

Identifying the underlying cause of the P0641 code can be difficult, especially if you’re not confident with your automotive knowledge. In most cases, it would be best to bring your vehicle to an auto repair shop and seek the help of a professional for an accurate diagnosis.

Here is a video that can help give you a better idea of how this trouble code might be diagnosed:

How to Fix the P0641 Code

The P0641 code is a generic trouble code that may apply to various makes and models. While vehicles from different manufacturers may share common symptoms, that doesn’t mean that they also share repair processes. For example, the steps for diagnosis and repair for a P0641 Chevy code may differ from those required by a P0641 Hyundai code.

If you’re an advanced DIYer who’d like to fix this code on your own, it will be helpful to refer to your repair manual or get factory vehicle repair information from an online subscription service.