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Technical Description of OBD-II Trouble Code
High Circuit Voltage in Sensor Reference “C”
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
Based on my experience, when encountering a stored P0699 trouble code, I understand that the powertrain control module (PCM) has detected a high reference voltage condition in a specific sensor labeled as “C”. I recall that this sensor is typically associated with the automatic transmission, transfer case, or front differential.
An additional sensor code will likely provide more specific information about the malfunction, with the P0699 indicating that the reference circuit voltage for sensor “C” is too high. To determine the location and function of the sensor in relation to the vehicle in question, I would consult a reliable vehicle information source like All Data DIY. If the P0699 code is stored alone, it could indicate a PCM programming error. I always prioritize diagnosing and repairing any other sensor codes before addressing the P0699, keeping in mind the higher than normal reference voltage condition, as it usually disappears once other more specific sensor codes are resolved.
I understand that the sensor in question is typically supplied with a reference voltage signal (usually five volts) through a switched circuit that is energized with the key on, as well as a ground signal. Based on my familiarity, I know that the sensor is likely of the variable resistance or electromagnetic type, and it completes the circuit in question. As a general rule, the sensor’s resistance should decrease as pressure, temperature, or speed increases, and vice versa. The PCM recognizes the voltage variations as changes in pressure, temperature, or speed. If the input voltage signal received by the PCM exceeds a programmed limit, a P0699 code will be stored and the malfunction indicator lamp (MIL) may illuminate. In some models, multiple drive cycles with a failure may be required for the MIL to illuminate. I consider it a successful repair when the PCM enters readiness mode after performing the necessary repairs. I clear the code and drive the vehicle normally before returning it to the customer. If the PCM enters readiness mode, it indicates a successful repair. If the code is reset and the PCM does not enter readiness mode, it indicates that a malfunction is still present.
Severity & Symptoms
The severity of a stored P0699 code depends on which sensor circuit is experiencing the high reference voltage condition. The accompanying codes must be taken into account before determining the degree of severity.
Symptoms of a P0699 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
Before starting the diagnosis for a P0699 code, it is recommended to have a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source like All Data DIY. A portable oscilloscope can also be useful in this diagnosis.
I would begin by consulting the vehicle information source to determine the location and function of the sensor in relation to the specific vehicle. I would then visually inspect the wiring harnesses and connectors related to the sensor circuit. Any damaged or burned wiring, connectors, or components should be repaired or replaced as necessary.
Next, I would connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes and freeze frame data. I would write down the codes, along with the order in which they were stored, and any related freeze frame data, as this information may be helpful if the code is intermittent. After that, I would proceed to clear the codes and test drive the vehicle to see if the code is reset.
If the code is immediately reset, I would use the DVOM to test the reference voltage and ground signals at the sensor in question. I would expect to find five volts and a ground at the sensor connector.
If the voltage and ground signals are present at the sensor connector, I would likely continue by testing the sensor’s resistance and continuity levels. I would refer to the specifications provided by the vehicle information source and compare my actual findings to them. Sensors that do not comply with these specifications will need to be replaced.
Before testing the resistance with the DVOM, I always disconnect all related controllers from the system circuits to avoid potential PCM damage. If the reference voltage is high at the sensor, I would use the DVOM to check the circuit resistance and continuity between the sensor and the PCM. Any shorted circuits should be replaced as necessary.
If the sensor in question is electromagnetic and has a reciprocating signal, I would use the oscilloscope to monitor live data, paying attention to spikes, glitches, and maxed out circuits.
Additional diagnostic notes:
Professional Service
While we always recommend seeking professional mechanical assistance to resolve this issue, if for some reason that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to be addressed. If you are interested in this option, please upload your ECU file to our portal.
