U0100
Lost Communication With ECM/PCM "A"
OBD-II
Wiring / network
What it means
Other modules cannot reach the engine controller — check power, grounds, and CAN wiring before suspecting the module.
Seeing U0100?
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Check your car freeRelated codes
U0001
High Speed CAN Communication Bus
Wiring / networkHigh
U0002
High Speed CAN Communication Bus Performance
Wiring / networkHigh
U0003
High Speed CAN Communication Bus (+) Open
Wiring / networkHigh
U0004
High Speed CAN Communication Bus (+) Low
Wiring / networkHigh
U0005
High Speed CAN Communication Bus (+) High
Wiring / networkHigh
U0006
High Speed CAN Communication Bus (-) Open
Wiring / networkHigh
U0007
High Speed CAN Communication Bus (-) Low
Wiring / networkHigh
U0008
High Speed CAN Communication Bus (-) High
Wiring / networkHigh
General reference only — what a code means can vary by make and model. Confirm with a qualified technician.