P0697: Sensor Reference Voltage C Circuit Open (Meaning, Causes, Fixes)
What P0697 means
The powertrain control module (PCM) sends a reference voltage, typically 5 volts, to many sensors through a switched circuit that is powered with the key on. Each sensor changes that signal based on what it measures (pressure, temperature or speed) and sends it back. OBD-Codes.com explains that if the PCM doesn't receive the expected input voltage from a sensor on circuit "C", it considers the circuit open and stores P0697. RepairPal says the PCM sends the 5 volt reference to all applicable engine sensors and sets P0697 when it detects an issue with that signal. Which sensors share circuit "C" depends on the vehicle, and the manufacturer's repair information lists them. The sources differ on which sensors are usually involved: OBD-Codes.com says the sensor is typically tied to the automatic transmission, transfer case or a differential, that P0697 almost always appears with a more specific sensor code, and that if it is stored alone a PCM programming error is likely. RepairPal describes it as the reference for engine sensors and lists only "engine may not start" as a symptom. Related codes are P0698 (reference voltage C circuit low) and P0699 (reference voltage C circuit high), and P0641 is the same fault on reference circuit "A".
Severity: can I keep driving?
Drive with caution, fix soon
Get it diagnosed within a reasonable time. RepairPal rates P0697 Moderate, meaning it may not threaten safety or drivability right away, but it lists "engine may not start" as the symptom. OBD-Codes.com says how serious it is depends on which sensor circuit is open and what other codes are stored with it. If the transmission shifts badly or won't engage, 4WD won't switch, or the speedometer stops working, drive gently and get it checked before relying on the car.
Common symptoms
- Check engine light on, though some vehicles need several failed drive cycles before it lights (OBD-Codes.com)
- Engine may not start (RepairPal)
- Transmission shifting problems, including failure to switch between sport and economy modes (OBD-Codes.com)
- Delayed or no transmission engagement (OBD-Codes.com)
- 4WD or AWD that won't switch modes, a transfer case that won't shift between low and high, or front differential or hubs that won't engage (OBD-Codes.com)
- Erratic or dead speedometer or odometer (OBD-Codes.com)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Open circuit or bad connector in the sensor reference wiring (OBD-Codes.com; RepairPal lists a wiring issue)
- Blown fuse or fusible link (OBD-Codes.com)
- Faulty system power relay (OBD-Codes.com)
- Bad sensor on the reference circuit (OBD-Codes.com; RepairPal lists engine sensor failure)
- PCM failure, or a PCM programming error if P0697 is stored with no other sensor codes (RepairPal lists PCM failure; OBD-Codes.com suggests a programming error)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Read all stored codes and write them down with any freeze frame data. Fix any more specific sensor codes first, since P0697 usually appears alongside them (OBD-Codes.com).
- Check the related fuses and fusible links. OBD-Codes.com notes a fuse can look fine with little load and fail under full load, and a blown fuse usually points to a short somewhere.
- Inspect the sensor wiring harnesses and connectors for damage or burning (OBD-Codes.com).
- After any repair, clear the code and drive normally. OBD-Codes.com says if the PCM enters readiness mode the repair worked; if the code returns, the problem is still there.
Typical fixes
- Replace a blown fuse or fusible link, and find the short that blew it (OBD-Codes.com)
- Repair an open or damaged wire or connector between the sensor and the PCM (OBD-Codes.com, RepairPal)
- Replace a faulty system power relay (OBD-Codes.com)
- Replace a sensor that fails the manufacturer's resistance or continuity specs (OBD-Codes.com, RepairPal)
- Reprogram or replace the PCM only after the wiring and sensors test good (OBD-Codes.com, RepairPal)
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- Testing means checking for 5 volts and a good ground at the sensor connector, then circuit resistance and continuity back to the PCM with the related controllers disconnected; OBD-Codes.com says an oscilloscope can help with electromagnetic sensors
- The car won't start, or the transmission or 4WD isn't engaging properly
- P0697 is the only code stored, which OBD-Codes.com says points to a possible PCM programming error
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0697 serious?
RepairPal rates it Moderate but lists "engine may not start" as a symptom. OBD-Codes.com says it depends on which sensor circuit is affected and what other codes are stored, and lists shifting and 4WD engagement problems as possible symptoms.
Can I drive with P0697?
Often, if the car starts and drives normally, but get it diagnosed soon. If shifting, gear or 4WD engagement, or the speedometer is affected, limit driving until it's checked.
Which sensor causes P0697?
It depends on the vehicle; the manufacturer's repair information lists which sensors share reference circuit C. OBD-Codes.com says it's usually a transmission, transfer case or differential sensor, while RepairPal describes it as an engine sensor reference.
How much does it cost to fix P0697?
Neither source gives a repair cost. It can range from a fuse, wire or connector repair to a new sensor or relay, or rarely PCM work, so get a diagnosis and a written estimate first.
Sources
Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.