U0156–U0157 Lost Communication With Information Center A

Which code is which

Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.

The definition

U0156: Lost Communication With Information Center A.

U0156 is a network code (communication between control modules), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.

What to check first

Cheapest and fastest checks first:

1. Check power and earth at the module first - a module with no supply cannot answer.
2. Check the two data-bus wires for continuity and for a short between them.
3. Scan the other modules: if several report the same module missing, the fault is at that module rather than on the bus.

What actually causes this on a VAG

A module has stopped hearing from the car's display or information unit. Which unit that actually is depends on the model - it can be the central screen and head unit, or the driver's information display in the instrument cluster. Those live in different places and are wired differently, so the scan has to tell you which module reported the fault and which one has gone missing before the diagnosis means anything. Symptoms range from a blank or frozen screen to no sound, no phone and no navigation all at once. How the infotainment units are joined together matters here, and it changed between generations. Through the MMI and RNS era, Audi and VW linked the infotainment components in a fibre-optic ring - VAG's own diagnostics call it the optical data bus. A ring only works if every unit in it is present, powered and awake, so one missing or unplugged unit takes the whole loop down. Newer infotainment systems are joined by ordinary copper networks instead, where losing one unit does not take the rest with it. Establish which kind your car has before you start reasoning about it: advice written for the fibre-optic cars is actively misleading on the newer ones.

Most likely causes, in order

1. Aftermarket work or a removed module. On a fibre-optic car, unplugging or removing any unit in the loop - an amplifier, a phone module, a tuner, a changer - breaks the whole ring unless a proper bypass is fitted in its place. On a copper-networked car it won't kill the lot, but the same job can still leave a plug off or a wire pinched. Either way, if a stereo, amp, DAB or phone kit has recently been fitted or taken out, that work is the first thing to revisit.
2. Low voltage, a flat battery or a jump start. Infotainment modules are sensitive to supply drops and frequently log communication faults after a battery has gone flat or been disconnected. If the car has had starting trouble or has been standing, have the battery tested and the code cleared before chasing anything else.
3. A loose or damaged connector, or a damaged fibre. Plugs behind the dash get disturbed during trim, dash or windscreen work. Fibre-optic leads in particular do not tolerate being kinked, pinched or pulled tight - and on these cars a crushed fibre has its own signature, because VAG stores a fault for the optical bus attenuation being too high. A damaged lead otherwise looks exactly like a failed module.
4. A failed unit in the loop or on the network. Genuine failures do happen, most often to a unit that lives somewhere warm or damp. Which one it is has to be established by tracing the network with a proper diagnostic tool, not by guessing at the most visible part.

Worth knowing: The dead screen in front of you is very often the innocent party. On these networked systems the real fault frequently sits at the other end - an amplifier or module in the boot, or a bypass that was never fitted when something was removed. Have a full scan done and note every infotainment module that has gone missing. If several disappear together, the problem is the network, not the display. And on the fibre-optic cars the diagnosis is less guesswork than it looks: the car stores faults naming the individual units on the optical bus, so ask for those to be read out rather than accepting a quote for the screen.

Common questions

What does U0156 mean?

U0156 means Lost Communication With Information Center A. This module has stopped talking on the car's data network, so nothing else can hear it.

Can I drive with U0156?

The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.

Related reading

• Several warning lights on at once: usually one cause, not many
• Do you actually need a VAG-specific scan tool?
• Key not recognised or car won't unlock: VW and Audi
• Why the same fault code has completely different causes