What Does It Mean?
This diagnostic code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
When faced with a stored P0699 fault code, I know from experience that the powertrain control module (PCM) has detected a high reference voltage condition for a specific sensor labeled “C”. I recall that the sensor in question has always been related to the automatic transmission, transfer case, or front differential.
An additional sensor code will likely point me in the specific direction of the malfunction, with P0699 adding that the reference voltage for sensor “C” circuit is too high. To determine the location (and function) of the sensor for the specific vehicle, I would consult a reliable vehicle information source like All Data DIY. If P0699 was stored alone, I would suspect a PCM programming error occurred. I always diagnose and repair any other sensor codes before addressing P0699 – keeping in mind the above-normal reference voltage condition – as it will usually disappear once other (more specific) sensor codes are fixed.
I understand that the sensor in question is normally powered by a reference voltage signal (typically five volts) through a switched circuit (powered with ignition on) and a ground signal. Experience dictates that the sensor will be either variable resistance or electromagnetic type and will complete the circuit in question. Typically, sensor resistance should decrease as pressure, temperature, or speed increases and vice versa. When the sensor’s resistance level changes (under varying conditions) and the circuit voltage responds; the PCM recognizes voltage variations as changes in pressure, temperature, or speed. If the input voltage signal received by the PCM exceeds a programmed limit, P0699 will be stored and a malfunction indicator light (MIL) may illuminate. Some models require multiple drive cycles (with failure) for the MIL to illuminate. Good things happen when I allow the PCM to enter readiness mode before considering a repair successful. I clear the code once repairs are made and drive the vehicle normally (before returning it to the customer). If the PCM enters readiness mode, the repair was successful. If the code resets, the PCM won’t enter readiness mode and I know a malfunction is still present.
Severity and Symptoms
The urgency of a stored P0699 depends on which sensor circuit is experiencing the high reference voltage condition. Accompanying codes must be considered before determining severity level.
Symptoms of a P0699 code may include:
Delayed (or no) transmission engagement
Transmission failure to switch between sport and economy modes
Transmission shifting malfunctions
Transmission failure to switch between four-wheel drive and two-wheel drive modes
Transfer case failure to shift from low to high range
Lack of front differential engagement
Lack of front hub engagement
Erratic or inoperative speedometer/odometer
Causes
Possible causes of this engine code include:
Shorted circuits and/or connectors
Faulty sensor
PCM programming error or defective PCM
Diagnostic and Repair Procedures
Before starting my diagnosis for P0699, I prefer to have a diagnostic scanner, digital volt/ohmmeter (DVOM), and reliable vehicle information source (like All Data DIY). I’ve also found that a portable oscilloscope can be helpful in this diagnosis.
I would begin by consulting my vehicle information source to determine the sensor’s location and function for the specific vehicle. I would continue by performing a visual inspection of wiring harnesses and connectors related to the sensor circuit. I would repair or replace damaged or burned wiring, connectors, and components as needed.
Next, I prefer to connect the scanner to the vehicle’s diagnostic port and retrieve all stored fault codes and freeze frame data. I write down the codes, the order in which they were stored, and any associated freeze frame data, as this information may prove useful if the code proves intermittent. Then I would proceed to clear the codes and test the vehicle to see if it resets.
If the code immediately resets, I would use the DVOM to test reference voltage and ground signals at the sensor in question. I would expect to find five volts and ground at the sensor connector.
I would probably continue by testing the sensor’s resistance and continuity levels if voltage and ground signals are present at the sensor connector. I can obtain specifications from my vehicle information source and compare my actual results with them. Sensors not meeting these specifications will need replacement.
I always disconnect all associated controllers from system circuits before testing resistance with the DVOM because I know this could cause PCM damage. If reference voltage is high (at sensor level), use the DVOM to check circuit resistance and continuity between sensor and PCM. Replace shorted circuits as needed.
If the sensor in question is electromagnetic with alternating signal, use the oscilloscope to monitor live data. Focus on spikes, glitches, and maximized circuits.
Additional Diagnostic Notes:
This type of code is usually provided as support for a more specific code
A stored P0699 code is normally associated with the transmission