What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles. Although generic, specific repair steps may vary by make/model.
If your OBD II equipped vehicle has a stored P0698, it means the Powertrain Control Module (PCM) has detected a low reference voltage signal for a specific sensor designated “C”. The sensor in question is typically associated with automatic transmission, transfer case, or one of the differentials.
A more specific sensor code will almost always accompany this code. P0698 adds that the sensor reference circuit voltage is low. To determine the location (and function) of the sensor regarding the vehicle in question, consult a reliable vehicle information source (All Data DIY is an excellent source). Suspect a PCM programming error if P0698 is stored alone. You’ll need to diagnose and repair any other sensor codes before diagnosing and repairing P0698 – but keep the low reference voltage condition in mind.
The sensor in question receives reference voltage (typically five volts) through a switched circuit (powered with ignition on). There will also be a ground signal. The sensor will be either variable resistance or electromagnetic type and will complete the circuit. Sensor resistance should decrease as pressure, temperature, or speed increases and vice versa. When sensor resistance changes (under varying conditions), it provides the PCM with an input voltage signal.
If the input voltage signal received by the PCM is below a programmed threshold, a P0698 will be stored. A Malfunction Indicator Lamp (MIL) may also illuminate. Some vehicles require multiple drive cycles (with failure) for MIL illumination. Allow the PCM to enter readiness mode before considering repair successful. Simply clear the code after repairs and drive the vehicle normally. If the PCM enters readiness mode, the repair succeeded. If the code resets, the PCM won’t enter readiness mode and you know a malfunction still exists.
Severity and Symptoms
The severity of a stored P0698 depends on which sensor circuit is experiencing low voltage condition. Other stored codes must be considered before determining severity.
Symptoms of a P0698 code may include:
- Transmission failure to switch between sport and economy modes
- Transmission shifting malfunctions
- Delayed (or no) transmission engagement
- 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
Possible causes of this engine code include:
- Faulty sensor
- Defective or blown fuses and/or fuse links
- Faulty system power relay
- Open circuits and/or connectors
Diagnostic and Repair Procedures
A diagnostic scanner, digital volt/ohmmeter (DVOM), and reliable vehicle information source (such as All Data DIY) will be needed to diagnose a stored P0698 code. A portable oscilloscope may also prove useful in your diagnosis.
First, consult your vehicle information source to determine the location and function of the sensor in question regarding your specific vehicle. Perform visual inspection of wiring harnesses and connectors related to the sensor system. Repair or replace damaged or burned wiring, connectors, and components as needed. Second, connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes and freeze frame data. Document the codes, the order they were stored, and any associated freeze frame data, as this information may prove useful if the code proves intermittent. You may now proceed to clear the code; then test drive the vehicle to see if it immediately resets.
If the code immediately resets, use the DVOM to test reference voltage and ground signals at the sensor in question. You would normally expect to find five volts and ground at the sensor connector.
Continue by testing sensor resistance and continuity levels if voltage and ground signals are present at the sensor connector. Obtain test specifications from your vehicle information source and compare your actual results to them. Sensors not conforming to these specifications should be replaced.
Disconnect all associated controllers from system circuits before testing resistance with the DVOM. Failure to do so may result in PCM damage. If reference voltage is low (at sensor level), use the DVOM to check circuit resistance and continuity between sensor and PCM. Replace open or shorted circuits as needed. If the sensor in question is electromagnetic with alternating signal, use the oscilloscope to monitor data. Focus on completely open circuits and issues.
Additional Diagnostic Notes:
This type of code is typically provided as support for a more specific code
A stored P0698 code is normally associated with transmission