Symptom
Door or boot shows as open when it is shut
The car insists something is open when everything is closed — an interior light that will not go out, a warning that will not clear, a car that refuses to lock or arm its alarm. The vehicle decides this from a small switch inside each latch, and those switches live in the wettest and dirtiest part of the car and are the commonest thing to fail on it. The consequence is more than an annoyance: a car that believes a door is open often will not power down, which flattens a healthy battery over a few days and gets answered with a new one.
Also described as: door ajar warning, says door is open, boot shows open, interior light stays on, car wont lock, door open warning wont clear, door or trunk shows as open when it is shut, trunk shows open, نشان میدهد در باز است, چراغ در باز روشن میماند, avisa puerta abierta, maletero marca abierto, sensor puerta mal, cajuela marca abierta, يقول الباب مفتوح وهو مغلق, الشنطة تظهر مفتوحة, حساس الباب غلط
What this usually means
The vehicle decides this from a small switch inside each latch, and those switches live in the wettest and dirtiest part of the car and are the commonest thing to fail on it. That is the whole diagnosis for most of these, and the repair is a latch rather than anything electronic.
The consequence is more than an annoyance: a car that believes a door is open often will not power down, which flattens a healthy battery over a few days and gets answered with a new one. That connection is the reason this entry matters — a car needing a jump start after a quiet week, with an interior light that will not go out, has one fault and not two.
Which door it names is usually correct, and the interior light and the dashboard message agree. Where the car names no particular door, or names one that is plainly shut, read the live latch states on a scan tool — every door reports its own, and the odd one out identifies itself in seconds.
The boot and the bonnet are worth checking even when the message names a door, because on some vehicles they share a circuit and a message.
Water and corrosion are the mechanism, so a fault that appears in winter or after a wash and clears in dry weather is the same switch at an earlier stage. Cleaning and lubricating a latch sometimes resolves it entirely, and is worth trying before the part is ordered.
And a car that will not arm its alarm is reporting the same thing — the alarm refuses to set while it believes an opening is unsecured, which is correct behaviour rather than an alarm fault.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Interior light will not go out, one door named | That door's latch switch — the commonest failure on the car | Read live latch states; the odd one out identifies itself. The named door is usually correct. | Clean and lubricate the latch first; renew it if that does not resolve it. |
| Battery flat after standing a few days | The car will not power down while it believes something is open — one fault, two symptoms | Measure quiescent current and check latch states. A car that will not sleep is the mechanism. | Repair the latch. Fitting a battery treats the symptom and it will happen again. |
| No particular door named, or one named that is plainly shut | A switch reporting wrongly, or the boot or bonnet sharing the circuit | Read every latch state live, including boot and bonnet. Some vehicles share a message. | Repair whichever reports wrongly. |
| Appears in winter or after a wash, clears in dry weather | Water and corrosion in the latch — the same fault at an earlier stage | Correlate with weather. Intermittency by season is characteristic. | Clean, dry and lubricate the latch. It will progress to a permanent fault if left. |
| Alarm will not arm | The same belief — the alarm correctly refuses to set with an opening reported unsecured | Not an alarm fault. Read latch states rather than diagnosing the alarm. | Repair the latch switch; the alarm arms again. |
| Message appeared after work on a door or the boot | A connector not remade, or a latch disturbed and not fully seated | Retrace the work before reading anything else. | Reseat the connector or the latch. Cheapest cause and it dates itself. |
-
Interior light will not go out, one door named
- Likely cause
- That door's latch switch — the commonest failure on the car
- How to confirm it
- Read live latch states; the odd one out identifies itself. The named door is usually correct.
- What fixes it
- Clean and lubricate the latch first; renew it if that does not resolve it.
-
Battery flat after standing a few days
- Likely cause
- The car will not power down while it believes something is open — one fault, two symptoms
- How to confirm it
- Measure quiescent current and check latch states. A car that will not sleep is the mechanism.
- What fixes it
- Repair the latch. Fitting a battery treats the symptom and it will happen again.
-
No particular door named, or one named that is plainly shut
- Likely cause
- A switch reporting wrongly, or the boot or bonnet sharing the circuit
- How to confirm it
- Read every latch state live, including boot and bonnet. Some vehicles share a message.
- What fixes it
- Repair whichever reports wrongly.
-
Appears in winter or after a wash, clears in dry weather
- Likely cause
- Water and corrosion in the latch — the same fault at an earlier stage
- How to confirm it
- Correlate with weather. Intermittency by season is characteristic.
- What fixes it
- Clean, dry and lubricate the latch. It will progress to a permanent fault if left.
-
Alarm will not arm
- Likely cause
- The same belief — the alarm correctly refuses to set with an opening reported unsecured
- How to confirm it
- Not an alarm fault. Read latch states rather than diagnosing the alarm.
- What fixes it
- Repair the latch switch; the alarm arms again.
-
Message appeared after work on a door or the boot
- Likely cause
- A connector not remade, or a latch disturbed and not fully seated
- How to confirm it
- Retrace the work before reading anything else.
- What fixes it
- Reseat the connector or the latch. Cheapest cause and it dates itself.
Codes that produce this symptom (14)
Listed with the codes that most typically present this way first — the likeliest place to start.
- U0215 Lost Communication With Door Switch A Typical of this code Low
- U0216 Lost Communication With Door Switch B Typical of this code Low
- U0217 Lost Communication With Door Switch C Typical of this code Low
- U0218 Lost Communication With Door Switch D Typical of this code Low
- U0219 Lost Communication With Door Switch E Typical of this code Low
- U0220 Lost Communication With Door Switch F Typical of this code Low
- U0221 Lost Communication With Door Switch G Typical of this code Low
- U0516 Invalid Data Received From Door Switch A Typical of this code Low
- U0517 Invalid Data Received From Door Switch B Typical of this code Low
- U0518 Invalid Data Received From Door Switch C Typical of this code Low
- U0519 Invalid Data Received From Door Switch D Typical of this code Low
- U051A Invalid Data Received From Door Switch E Typical of this code Low
- U0521 Invalid Data Received From Door Switch F Typical of this code Low
- U0522 Invalid Data Received From Door Switch G Typical of this code Low
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.
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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.
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