U0147: Lost Communication With Serial Data Gateway Module B
What to do
Expect the connected features to stop — the phone app, live traffic, online services, hands-free calling — while the car itself drives normally.
That combination is deliberate. On many modern cars this second gateway is a barrier between the parts of the car that can be reached from outside — telematics, keyless entry, phone and media — and the parts that steer, brake and drive it. When it stops passing messages, the connected features go and the car keeps working. That is the design doing its job.
One thing worth treating as more than an inconvenience: the automatic emergency call may have gone with it. On many cars that system sits behind this gateway, and there is no symptom at all to tell you — see U0198.
And the question that usually finds the fault is what has been added rather than what has broken. A tracker, insurance box, dashcam, or plug-in dongle gets wired in exactly here, because it is where the useful data crosses. Mention anything of that kind, including anything a previous owner had fitted — a poor installation is a common cause of both this fault and a battery that goes flat over a weekend.
What this code means
A second gateway module has stopped being heard from. See U0146 for what a silent gateway does to everything behind it, and U0448 for why a vehicle carries more than one — increasingly as a deliberate security boundary between the modules that can be reached from outside the vehicle and the ones that steer, brake and drive it.
That boundary explains the symptom pattern, and it is a good outcome rather than a bad one. A silent gateway on the outward-facing side takes out connected services, the phone app, live traffic and hands-free calling while the vehicle drives entirely normally — which is exactly what the separation was built to achieve.
Two things are worth raising anyway.
The emergency call may have gone with it. On many vehicles the telematics module sits behind this gateway, so the automatic post-crash call is unavailable and nothing about driving says so — see U0198.
And this is the gateway an aftermarket device is most often spliced into, because it is where the useful data crosses. A tracker, insurance box, dashcam or fleet terminal wired in here is a common cause of both this code and a battery that flattens over a weekend, since a device that keeps reading the network stops the vehicle sleeping.
So the question that finds it is what has been added rather than what has broken, and it should be asked about work a previous owner had done as well.
Likely causes
Start here
- Poor wiring splice in an aftermarket installation · moderate
- Blown fuse or failed supply · easy
- Corroded or loose connector · easy
- Failed power or earth supply to the module · moderate
Less common
- Damaged data bus wiring · moderate
- Faulty gateway module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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