U0240 code meaning
Lost Communication With Entrapment Control Module B
What U0240 means
U0240 flags the second anti-trap unit, entrapment control module B, as missing on the network. Where a vehicle has more than one automatically closing panel, for example a sunroof plus a power sliding door, each may carry its own reversal electronics, and B denotes one of them as assigned by the maker; no manufacturer documents U0240 publicly. The protection itself is defined by FMVSS 118, which limits the squeezing force and requires reversal before a test rod is trapped, and by the reversal logic in anti-pinch modules that compare motor current with a learned profile. GM's lost communication logic still applies: a periodic status message stays away with supply at 9-16 V. Pair with U0239 for module A. Automatic closing may be disabled; no MIL.
U0240 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0240
- Automatic close function of a panel disabled
- Panel only moves while the switch is held
Common causes of U0240
- Most likelyModule B without power or ground
- PossibleWiring broken in a moving harness (sliding door, roof frame)
- Less likelyEntrapment control module B faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Entrapment module bCAN bus
What each part of U0240 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 40 | The exact fault in that area. |
What to do next
- Note U0240 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0240
What does U0240 mean?
U0240 means "Lost Communication With Entrapment Control Module B". U0240 flags the second anti-trap unit, entrapment control module B, as missing on the network. It is a generic code, so it means the same on every make.
Is it safe to drive with U0240?
U0240 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0240 fail an emissions test?
U0240 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0240 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0240 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.