Sensor Reference Voltage "C" Circuit High
P0699 indicates the sensor reference voltage 'C' circuit is reading higher than the acceptable range, typically above 5.5 volts when it should be around 5 volts. This code often appears alongside more specific sensor codes and may resolve once those primary issues are addressed. The high voltage condition suggests a wiring fault, voltage regulator failure, or sensor circuit problem.
What You Might Notice
- Check engine light illuminated
- Transmission engagement delay or failure
- Erratic transmission behavior
- Poor fuel economy
- Engine may run rough or hesitate
Most Common Causes
- 1
Wiring short to power
The sensor reference voltage circuit is shorted to battery voltage, causing the reference line to read higher than 5 volts. Check for damaged, pinched, or corroded wiring in the sensor circuit.
- 2
Faulty voltage regulator
The PCM's internal voltage regulator that supplies the 5-volt reference signal has failed or is outputting excessive voltage. This component controls the reference voltage for multiple sensors.
- 3
Defective sensor
The sensor itself may be failing and pulling excessive current or providing a high resistance value that causes the reference voltage to read high.
- 4
Ground circuit fault
A poor ground connection in the sensor circuit or loose ground terminal can cause voltage reference readings to spike abnormally.
How to Diagnose It
- 1
Check Wiring short to power — The sensor reference voltage circuit is shorted to battery voltage, causing the reference line to read higher than 5 volts. Check for damaged, pinched, or corroded wiring in the sensor circuit.
- 2
Check Faulty voltage regulator — The PCM's internal voltage regulator that supplies the 5-volt reference signal has failed or is outputting excessive voltage. This component controls the reference voltage for multiple sensors.
- 3
Check Defective sensor — The sensor itself may be failing and pulling excessive current or providing a high resistance value that causes the reference voltage to read high.
- 4
Check Ground circuit fault — A poor ground connection in the sensor circuit or loose ground terminal can cause voltage reference readings to spike abnormally.
How to Fix It
- 1
Inspect and repair wiring
Carefully inspect the sensor reference voltage 'C' circuit wiring for damage, corrosion, or short-to-power conditions. Repair or replace damaged wiring and ensure all connectors are clean and fully seated.
- 2
Check and clean ground connections
Locate the sensor ground connection and PCM ground terminals. Clean any corrosion, tighten all ground connections, and verify continuity to the battery negative terminal.
- 3
Test voltage regulator output
Use a multimeter to measure the reference voltage at the sensor connector. If voltage exceeds 5.5 volts, the PCM voltage regulator may be faulty and the PCM may require replacement or reprogramming.
- 4
Replace suspect sensor
If wiring and grounds are confirmed good and voltage is still high, the sensor itself may be defective. Replace the sensor on circuit 'C' with a factory or equivalent part.
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