U0249: Lost Communication With Entertainment Control Module — Rear B
What to do
The car drives normally and nothing important is affected — rear screens or headphones will have stopped working.
Try a reset first. These units are computers and they do hang; locking the car and leaving it long enough to fully power down often brings them back, and many have a hard reset in the handbook. If it returns and stays, nothing was broken.
Then think about what happens to the back of your car. Screens in headrests or seat backs have wiring that crosses the seat's fold line, so rear seats folded down regularly for luggage stress that wiring in one spot — a very common cause. Kicked seat backs, screens pulled on to adjust them, and things forced into media sockets do the same.
And have the battery checked: low voltage makes these modules drop off the network exactly as a failure would.
What this code means
The second rear entertainment control module has stopped being heard from. See U0237 for the ring-network reasoning and U0245 for the front unit.
Rear entertainment is the least consequential thing on the vehicle's network and the most physically abused, and that combination is what this page is about. Screens in headrests or a roof console, headphone transmitters, media inputs and their controls — none of it affects the car in any way, and all of it is within reach of passengers, luggage and children.
The causes therefore skew mechanical rather than electronic. A headrest screen is pulled on to adjust it, a folding roof console is hung from, a seat back is kicked, a media socket has a connector forced into it. The wiring runs up seat backs or along the headlining to reach these units — through exactly the paths that get disturbed when seats are folded, removed or reclined.
Folding a rear seat is the specific thing worth asking about. On vehicles where the screens are in the headrests or the seat backs, the harness crosses the fold line, and a seat folded flat repeatedly stresses it in one place. A rear entertainment fault on a vehicle whose rear seats are folded regularly for luggage is that until shown otherwise.
And the U0245 advice about resets and battery voltage applies here too — these are computers, they hang, and they drop off the network when voltage is low. Trying a reset and testing the battery costs nothing and resolves a fair share.
Likely causes
Start here
- Damaged wiring harness · moderate
- Corroded or loose connector · easy
- Battery disconnected or module reprogrammed · easy
- Disconnected sensor connector · easy
Less common
- Damaged data bus wiring · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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