P0698: Reference voltage C is low, but the code does not name the attached sensor

P0698 identifies a low sensor-reference voltage C circuit in Ford's five-volt reference check. The channel letter identifies the monitored supply group, not a universal component location or a single named sensor.

A supply fault changes interpretation of sensor data

Ford's documented low criterion is reference voltage below 4.75 volts, with ignition on and a five-second monitoring duration. This is distinct from an individual sensor's signal voltage being low. If a reference supply is outside range, dependent readings require evaluation in that electrical context.

The summary does not list every sensor connected to reference C for every engine. Do not select a component merely because another vehicle uses the same channel letter for it; the circuit diagram must establish the actual connections.

Identify the controller's reference strategy

The page also describes a Bosch Tricore range/performance check with a different code and timing. That alternative does not replace P0698's published low-circuit criterion on all applications.

Preserve the complete DTC set and verify the reference at the points and under the conditions specified by the exact service procedure. The source labels the low condition as a short-to-ground category, but the code alone does not locate the short or prove the PCM has failed. Successful verification should establish a stable valid reference and then reassess any dependent sensor faults rather than replacing multiple sensors from their low readings alone.

Source and applicability

This explanation covers the cited Ford monitor variants, not every vehicle displaying this code. Match the engine, sensor architecture and calibration before applying numerical limits.

Ford OBD summary, PDF page 129, Ford OBD summary, PDF page 130.