U0078: Barramento de comunicação dos módulos de controle F — desligado
O que fazer
If this has been "fixed" before and keeps coming back, read this — because it may never have been fixed at all.
One of your car's computers deliberately stopped talking to the network to protect it — see U0073.
Here is the trap. On many cars, that computer rejoins the moment the fault codes are cleared. So the warning lights go out, everything works, and the car drives away.
That looks exactly like a repair and it is not one. The wiring fault is untouched, and the computer will withdraw again as soon as enough errors build up — which might be minutes or might be weeks.
So the question worth asking is not what was done, but what was found. "We cleared the codes and it was fine" is not a diagnosis, and a fault that has come back three times has probably never actually been investigated.
Ask what was measured, and what the result was.
One thing that genuinely helps: ask for the codes to be read and recorded before they are cleared, and then cleared once deliberately. That way the next occurrence is a clean record rather than a mixture of old and new faults, which makes it far easier to find.
O que este código significa
A module has taken itself off communication bus F. See U0073 for what bus off means and U0080 for what a sixth lettered network usually implies about the vehicle.
One point belongs here and it is about what a repair actually is: clearing the code is not one.
U0073 explains that recovery differs between designs — some modules rejoin automatically, some after an ignition cycle, some only when the fault memory is cleared. So on a good many vehicles, clearing the codes brings everything back to life.
And that is genuinely misleading, because it looks exactly like a repair. The module rejoins, the warning lamps go out, the vehicle drives away, and the underlying wiring fault is untouched. It returns as soon as enough errors accumulate again — which may be minutes or weeks depending on how marginal the fault is.
Which produces a pattern worth naming: a vehicle that has been "fixed" several times by having its codes cleared. Each visit ended with everything working. None of them changed anything.
So the instruction is to establish what was found rather than what was done. "The codes were cleared and it drove away fine" is not a diagnosis, and a fault that has come back three times has never actually been looked at.
And it is worth clearing the codes deliberately once, after reading them, precisely so that the next occurrence is a fresh record rather than a mixture of old and new — see U0064.
Causas prováveis
Comece aqui
- Fiação do barramento de dados danificada · moderado
- Conector corroído ou frouxo · fácil
- Falha intermitente na fiação · moderado
- Emenda de fiação malfeita em instalação de terceiros · moderado
Menos comum
- Outro módulo mantendo o barramento em nível baixo · especializado
- Resistor de terminação do barramento inoperante · especializado
Sintomas
Componentes envolvidos
Informação, não instrução
O CarGeek é uma referência, não um manual de serviço. Suas páginas são escritas a partir de fontes públicas e do que outras pessoas constataram, nunca a partir da documentação de serviço do fabricante, de modo que podem estar erradas ou incompletas para o seu veículo específico. Parte do que descrevem envolve risco real: alta tensão, combustível sob pressão, energia acumulada e peças quentes ou em movimento.
Antes de agir com base em qualquer orientação, peça a verificação de uma pessoa com formação técnica, seguindo o procedimento do próprio fabricante para o seu veículo. Nada aqui substitui esse procedimento.
Experiência da comunidade
Seja o primeiro a documentar isto
Ainda não há publicações sobre isto. Vale a pena anotar tudo o que você descobriu — até um beco sem saída poupa a mesma tarde de outra pessoa.
O que faz valer a leitura:
- O carro — marca, modelo, ano e motor. A mesma falha se comporta de forma diferente em cada um.
- O que você mediu, não só o que trocou.
- O que realmente resolveu — ou que nada resolveu, o que também vale saber.
Entrar ou criar uma conta para adicionar o que você descobriu sobre U0078.