What it means
The 5-volt sensor reference rail C is open — the module supplies no voltage on this circuit. Every sensor powered from reference C loses its supply and reads invalid, so the ECU substitutes default values and may limit engine operation. Causes: a broken reference wire, a disconnected connector, or an internal open in the module's voltage regulator for rail C.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine controller supplies a shared sensor reference rail called circuit C and monitors whether that reference is available. P0697 sets when the circuit C reference is open, so sensors powered from that rail may lose their supply and produce invalid readings; the cause may be wiring, a connector, or the controller's rail C supply.
Common causes
Most likely first.
- Open in shared reference rail
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
How to diagnose it
- Record freeze-frame data and scan for other sensor reference or signal codes that may identify which sensors share circuit C.
- Use the vehicle wiring diagram to identify circuit C sensors, then inspect their connectors and the shared reference wiring for disconnections, corrosion, or pushed-back pins.
- Check live data from the circuit C sensors for readings that are implausible or drop out together, which can point to a shared supply fault.
- Test for an open in the shared circuit C reference wire and its connector terminals using the manufacturer's procedure.
- If the harness and shared connections pass inspection, test the controller's circuit C reference output only as specified by the manufacturer.
Common fixes
- Reconnect a disconnected circuit C sensor or shared connector.
- Repair a pushed-back or corroded terminal in the circuit C reference path.
- Repair an open in the shared sensor reference wiring.
- Repair an internal module fault only after wiring and connected sensors have been checked by the specified procedure.
Can I keep driving?
Driving may be unreliable if circuit C sensors provide invalid data; the engine may run poorly, enter a limited operating mode, or fail to start. Avoid long trips if it runs abnormally, and stop if it stalls or cannot be controlled safely.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.