U3003 indicates that the vehicle’s control module has detected an abnormal battery voltage condition. It is a communication code used by many manufacturers to flag that the system voltage is outside the normal operating range.
A battery that cannot hold charge will cause the system voltage to drop below the module’s minimum threshold.
Poor connection increases resistance and can produce voltage fluctuations that trigger the code.
If the alternator does not maintain proper charging voltage, the system voltage can swing low or high enough to set U3003.
A broken wire, chafed harness, or bad ground can introduce voltage drops under load.
A rare internal fault in the PCM/ECM power circuit can misread voltage; this is much less common than external power‑source issues.
In most cases no. The PCM rarely fails on its own; the code is almost always caused by battery, alternator, wiring, or grounding problems.
Yes. An under‑voltage condition can lead to secondary codes related to fuel trim, misfire, or emission sensors because the modules receive insufficient power.
Clearing the code may turn off the warning temporarily, but if the underlying voltage issue remains, the code will return quickly.
Short trips are usually possible, but prolonged driving with an under‑charging battery or alternator can lead to a dead battery and loss of power‑assisted functions.