Error Code P0698 is defined as Sensor Reference Voltage C Circuit Low. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. It is related to the computer output circuit problems, including internal computer failure. In which case, the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) and another supporting control module, has detected a fault within the sensor reference voltage “C” circuit. Specifications on the definition, troubleshooting, and repairs may vary from one make and model to another.
Error Code P0698 means the PCM has detected a problem with the “C” circuit sensor reference voltage system, indicating a low reference voltage signal for the specific sensor.
The sensor in question is usually associated with the automatic transmission, transfer case, or one of the differentials. This code almost always comes with a more specific code. Thus, when diagnosing this code, it’s important to consult with a dependable vehicle information source (All Data DIY is a great choice) to determine sensor location (and function) as it relates to the vehicle in question.
If this code is stored and doesn’t come with other error codes, then you can suspect a programming error in the PCM. Other sensors must be diagnosed and repaired when dealing with this code, but the “C” circuit open issue must be kept in mind.
The reference voltage (usually 5V) is applied to the sensor in question through a switched (energized with the key on) circuit. There should also be a ground signal. And the sensor must be of either the variable resistance, or electromagnetic variety, and completes a specific circuit. As the pressure, temperature, and speed increases, the sensor resistance also decreases, and vice versa. As the resistance in the sensor changes with the conditions, it provides with the PCM and input voltage signal.
If the PCM receives an input voltage signal that is lower than expected, then Error Code P0698 will be stored.
In some cases, it may require multiple drive cycles before the Check Engine light lights up. With this, allow the PCM to enter readiness mode before considering any repairs as successful. Clear the codes after doing any repairs, and then take the vehicle for a test drive. If the PCM enters readiness mode, then the repair was successful. If the code comes back (resets), the PCM will not enter readiness mode, and the problem still persists.
The severity of symptoms for this code depends mostly with the sensor circuit experiencing the open condition. And as said earlier, this code almost always comes with other codes. Thus, it’s important to take note of those codes as well. Common symptoms for this code include:
- Transmission shifting malfunction
- Delayed (or no) engagement of the transmission
- Transmission unable to shift between sport and economy modes
- Transmission unable to shift between all-wheel and two-wheel drive modes
- Lack of from the engagement front hub
- Lack of engagement from the differential
- Inoperative or erratic speedometer/odometer
There are several problems that could lead to this code. Some of the most common causes are:
- Open circuits and connectors
- Blown or defective fuses and fusible links
- Faulty sensor power relay
- Bad sensor
How to Check
To diagnose this code, you will need a diagnostic scanner, DVOM (digital volt/ohmmeter), and a dependable vehicle information source. A portable oscilloscope can also help.
Determine the location and function of the sensors by consulting with the vehicle information source for the specific vehicle. Then, conduct a visual inspection of the sensor system, including all the connectors and harnesses. Repair or replace anything with signs of damage, such as burned wires, connectors, or various components.
Next, connect the scanner to the diagnostic connector of the vehicle and retrieve all stored codes. Write them down, along with their freeze frame data. Then, clear the code and test drive the vehicle to see if they set immediately.
If all system fuses are intact, and the code still resets immediately, then use the DVOM for test reference of the voltage and ground signal of the sensor in question. Typically, you can expect 5V and a common ground at the sensor connector.
If the voltage and ground single are present on the sensor connector, then continue testing the sensor resistance and continuity levels. Use the vehicle information source to get the right testing specs. Then, compare your findings. Sensors that are unable to comply with the specifications set by the manufacturer must be replaced.
Then, disconnect all related controllers from the system circuits before testing the resistance with the DVOM. If there are no reference voltage signals at the sensor, then disconnect all related controllers, and use the DVOM to check the circuit resistance and continuity between the sensor and the PCM. Open or shorted circuits must be replaced.
If the electromagnetic sensor is used, with a reciprocating signal, then use the oscilloscope to monitor live data. Pay attention to the glitches and completely open circuits.
How to Fix
Common repairs for this code include:
- Damaged electrical connectors, wirings, and various components must be replaced, as necessary
- Replacement of damaged or defective control modules (varies depending on which control module have detected the fault)
- Replacement of damaged (or defective) PCM
Since this code doesn’t specifically indicate how bad the voltage deficiency is, the seriousness of the problem varies from one case to another. However, since the sensor reference voltage “C” circuit is important for the operation of the engine, Error Code P0698 is an urgent concern. Thorough diagnosis and repairs must be conducted as soon as it appears.