P0698
UniversalSensor Reference Voltage C Circuit Low
Medium SeverityThis code indicates that the Powertrain Control Module (PCM) has detected a voltage reading lower than specified in the 'C' reference voltage circuit. This low voltage can impact the accuracy of various sensors connected to this circuit, potentially leading to noticeable performance issues or a no-start condition.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool down before working on any components. Disconnect the battery's negative terminal before performing any electrical diagnostics or repairs to prevent accidental short circuits or electrical shock. Use proper safety gear such as gloves and eye protection.
Common Symptoms
- Check Engine Light illuminated
- Engine may run rough or misfire
- Decreased engine performance
- Transmission shifting issues
- Engine may stall unexpectedly
- Engine may fail to start
- Other related diagnostic trouble codes (DTCs)
Common Causes
- Short to ground in the sensor reference voltage circuit
- Open circuit or high resistance in the reference voltage wiring
- Faulty sensor connected to the reference voltage C circuit pulling voltage down
- Damaged or corroded wiring or connectors
- Internal fault within the Powertrain Control Module (PCM)
Frequently reported on: General/Universal
Diagnostic Steps
- Connect an OBD-II scanner to confirm the P0698 code and check for any other related DTCs.
- Visually inspect the wiring harness and connectors associated with the 'C' reference voltage circuit for any signs of damage, fraying, corrosion, or loose connections.
- Locate the sensors that utilize the 'C' reference voltage circuit (consult a vehicle-specific wiring diagram). Disconnect one sensor at a time to see if the voltage returns to normal, which would indicate a faulty sensor.
- Using a multimeter, carefully test the reference voltage at the affected sensors and at the PCM connector to identify where the voltage drop occurs.
- Check for continuity and resistance in the reference circuit wiring to identify any shorts to ground or open circuits.
👨🔧 When to Call a Professional
If, after checking basic wiring and connectors, you cannot identify the cause of the low reference voltage, or if the problem persists, it is highly recommended to consult a professional automotive technician. Complex electrical diagnostics, especially involving the PCM, require specialized tools and expertise.
Commonly Asked Questions
What does "Sensor Reference Voltage C Circuit Low" mean?
It means the computer (PCM) detected that the 5-volt reference voltage it provides to a specific group of sensors (circuit C) is lower than it should be. This low voltage can cause sensors to send incorrect data.
Can I drive with a P0698 code?
It is not recommended. A low reference voltage can lead to inaccurate sensor readings, which can cause significant engine performance issues, potential damage to other components, or even a sudden stall, increasing safety risks.
How do I find which sensors are on "Circuit C"?
You will need a vehicle-specific repair manual or wiring diagram. These resources will show which sensors receive their 5-volt reference voltage from the PCM's "C" circuit.
Is this usually an expensive repair?
The cost varies greatly depending on the cause. A simple wiring repair might be inexpensive, while a faulty sensor or, in the worst case, a defective PCM could be quite costly. The diagnostic time for electrical issues can also add to the expense.
Could a bad sensor cause this code?
Yes, a faulty sensor on the "C" reference voltage circuit could internally short or draw excessive current, pulling the reference voltage down and triggering the P0698 code. Disconnecting sensors one by one can help identify if a specific sensor is the culprit.