U0400
Invalid Data Received
- Severity
- High
- Driving
- Drive only to a garage
A module is receiving data over the vehicle's data bus that it can tell is wrong, without naming which module sent it. The message is arriving intact but the values in it fail a plausibility check - out of range, a bad checksum, or a counter that stopped advancing. Because the source is not named, this code is a starting point rather than an answer: the module that is actually at fault will usually have stored its own code saying so.
Possible causes
- CommonA module somewhere on the bus sending values that cannot be true
- CommonLow or unstable system voltage
- CommonCorroded connector or damaged wiring corrupting messages
- PossibleA module recently replaced or updated with the wrong calibration
- PossibleAftermarket accessory spliced into the bus
What you might notice
- Warning light on for the system that depends on the data
- The affected function switching itself off
- Fault codes stored in more than one module
- Several unrelated systems behaving oddly at once
What to check, in order
- Read the codes from every module on the vehicle. This code does not name the sender, so the module that does name a fault is where to start - and there is almost always one.
- Check battery voltage and the earth points. An unstable supply is the most common reason several modules start producing values that fail plausibility checks.
- Find out what was worked on recently. This code appearing after a repair, a battery change or a module replacement usually points straight back at that work.
- Look for aftermarket wiring spliced into the bus - alarms, trackers, dash cameras, tow bar electrics. A badly-made splice corrupts messages without breaking the network.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
U00xxU01xxU02xxU03xxU04xxU05xxU06xxU07xxU08xxU09xxU0AxxU0BxxU0CxxU0DxxU0ExxU0FxxU10xxU11xxU12xxU13xxU14xxU15xxU16xxU17xxU18xxU19xxU1AxxU1BxxU1CxxU1DxxU1ExxU1FxxU20xxU21xxU22xxU23xxU24xxU25xxU26xxU27xxU28xxU29xxU2AxxU2BxxU2CxxU2DxxU2ExxU2FxxU30xxU31xxU32xxU33xxU34xxU35xxU36xxU37xxU38xxU39xxU3AxxU3BxxU3CxxU3DxxU3ExxU3Fxx