P0697 indicates the powertrain control module (PCM) has detected an open circuit in Reference Voltage 'C,' one of the 5-volt supply circuits the PCM uses to power certain sensors. The code is set when the PCM monitors its own reference voltage output and finds that the expected voltage is missing or significantly outside specification on that specific circuit. It is fundamentally a wiring or sensor issue, not an engine-performance problem in itself.
A broken wire, chafed insulation, or stretched terminal in the harness supplying 5 V to the affected sensors is the most common cause. Reference voltage wires are often near hot or moving components and are vulnerable to fatigue and abrasion.
A connector that has backed off, unseated, or has water and corrosion on the pins will produce a true open circuit. This is especially common on sensors exposed to underhood heat cycling and moisture.
If one of the sensors powered by Reference Voltage C fails internally open, it can pull the entire shared circuit down and trigger the code along with sensor-specific codes.
The PCM-side connector for the C reference circuit can develop terminal tension loss or corrosion, creating an open between the driver transistor inside the PCM and the harness.
Wiring that has been spliced, routed incorrectly, or chewed can show an open only after the insulation is disturbed, producing intermittent or hard faults.
The internal transistor that supplies Reference Voltage C can fail open. This is uncommon and should only be considered after the entire harness and every sensor on the circuit have been ruled out.
Usually the vehicle will still run, but one or more sensors on the C reference circuit may be reading incorrectly, which can affect transmission shifting, idle quality, or other drivability. It is reasonable to drive to a repair facility, but the code should not be ignored long-term.
It depends on the specific vehicle. Common sensors that share 5 V reference circuits include the throttle position sensor, manifold absolute pressure sensor, camshaft/crankshaft position sensors, and some transmission range or pressure sensors. The vehicle's wiring diagram is the only reliable way to confirm which sensors are on the C circuit.
No. In the vast majority of cases P0697 is caused by a wiring break, a bad connector, or a failed sensor on the shared 5 V reference circuit. Replacing or reprogramming the PCM without first proving the harness and sensors is almost always an unnecessary expense. The PCM should only be considered after the wiring and all sensors on the C circuit have been tested and ruled out.
Because multiple sensors typically share a single 5 V reference circuit, an open anywhere in that circuit will cause every sensor on it to read 0 V. The PCM therefore often sets P0697 along with low-voltage codes for each affected sensor, which is a useful clue during diagnosis.