DTC codes / P23xx · Ignition system and misfire / P23CB
P23CB indicates that the powertrain control module (PCM) has detected a low-voltage condition on the control circuit for the fuel rail heater, which is used on some diesel engines to warm the fuel in the rail for better cold-start performance and combustion stability. The PCM commands the heater on and monitors the circuit; when the voltage on the control wire stays below the expected threshold, it sets this code.
Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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