P0699 OBD-II Trouble Code:Sensor Reference Voltage “C” Circuit High

What the P0699 code means

A P0699 code denotes a fault in the sensor reference voltage “C” circuit. The controller area network (CAN) supplies its sensors with a 5-volt reference voltage.

The CAN bus is a series of sensors that can all communicate with each other and pass on information without the need for a host computer. With a P0699 code, the powertrain control module (PCM) or possibly another control module has detected this fault. Other control modules in the system may include:

• Alternative fuel control module
• Body control module
• Anti-lock brake control module
• Instrument panel control module
• Fuel injection control module
• Turbo control module
• Anti-theft module
• Cruise control module
• Traction control module
• Proximity alert module
• Climate control module

The letter “C” narrows down diagnosis to a particular area of the circuit, but not necessarily to a specific component or wire.

What causes a P0699 code?

When a sensor reference “C” malfunction occurs, a trouble code is registered and the Malfunction Indicator Lamp (MIL) will be illuminated. Code set parameters may vary from one make/model to the next – many require several drive cycles in order for the MIL to illuminate, while others will illuminate the MIL after the initial failure.

What are the symptoms of a P0699 code?

• Stored trouble code
• Hard start/no start
• Rough running engine
• Poor fuel economy

• [Lack of power](https://www.yourmechanic.com/services/loss-of-power-inspection

• Engine misfire

How does a mechanic diagnose a P0699 code?

A suitable OBD-II scanner/code reader and digital volt/ohmmeter will be necessary for diagnosis and repair. A specialized scanner such as Autohex or Tech II may be needed to determine the general area of the malfunction. A technician will also need a memory device of some sort for backup, should the PCM and any other controllers lose their information and require reprogramming. A detailed factory wiring diagram and schematic of all the CAN processors will also be a must.

• Start your diagnosis with a careful visual inspection of the connectors and wiring. Repair/replace any damaged, disconnected, shorted or corroded wiring or connectors. Retest the system.

• If wiring, connectors and components (including fuses) appear to be in good working order, connect the scanner to the diagnostic port and record any stored codes. Freeze frame the data. This will be extremely useful in tracking down any intermittent conditions that may have been the cause of the code being stored.

• Test drive the vehicle and see if codes return. If the code does not immediately return, it could be an intermittent problem. Intermittents can be quite tricky to diagnose and may need to be allowed to worsen and return before a correct diagnosis can be made.

• Look for loose or disconnected engine or transmission ground cables, straps or wires, sometimes left disconnected after a repair job.

Common mistakes while diagnosing P0699 code

With a CAN-equipped vehicle, stored codes are a reaction to a communications failure between modules. This makes it easy to misinterpret the code and move toward replacing components that have nothing to do with the CAN itself.

How serious is a P0699 code?

A vehicle with a P0699 code can run poorly or not at all.

What repairs can fix a P0699 code?

Repair/replacement of wiring, connectors, components or sensors/processors in the CAN system.

Additional comments for consideration for P0699 code

This is a repair that is best left to a trained, qualified technician who knows the latest in CAN system technology. To disconnect and test every single pin in the CAN bus can take up to 40 hours of labor, and a single misplaced volt/ohmmeter probe can wipe out literally all the memory in the network, requiring a complete reprogramming. A specialized scanner such as Autohex can perform diagnostics by monitoring the system while the vehicle is being driven.

Need help with a P0699 code?

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