BMW fault 2DDA - No message from CAS
P3211 · U1131 · P3212 · U111E · U111F
Description
2DDA is logged by the DME when it stops receiving valid CAN messages from the CAS (Car Access System) module. CAS manages authorization, terminal status (ignition power states), and anti-theft authentication, and shares a rolling code with the DME to authorize engine start. When CAS communication is lost the DME typically cannot authenticate and the engine will not start, or will stall shortly after starting.
This code has 3 variants with different causes and fixes. Pick the one your scanner reported.
2DDA / P3211, U1131 Timeout
The DME expects cyclic CAS messages including terminal status and authorization data. After approximately 400 ms with no messages once bus activity is active, this variant sets. This is the "CAS is offline" variant, often accompanied by a no-start condition because CAS authorization is a prerequisite for engine operation.
Symptoms (4)
- Crank-no-start or no-crank-no-start, depending on how severely CAS has failed.
- Key may not be recognized.
- Dashboard may show reduced function with limited instrument cluster wake.
- Comfort Access may fail, with doors unresponsive or push-button-start not working.
Common Causes (5)
- Low battery or recent deep discharge. CAS is particularly sensitive to voltage events and many 2DDA complaints trace to battery condition.
- Water damage to the CAS module. The module is located near the steering column and has a known history of water ingress.
- Blown CAS fuse.
- CAS module internal failure after an overvoltage event (jump-start without correct procedure, alternator surge).
- CAN wiring fault between CAS and the rest of the bus.
Diagnosis Steps (5)
- Test the battery first. Measure resting voltage, loaded voltage during cranking, and charging voltage. CAS is more voltage-sensitive than most modules. Replace or charge a suspect battery before further diagnostics.
- Attempt CAS communication in ISTA or INPA. If CAS does not respond, treat as an offline module.
- Check CAS fuses and power supply per the wiring diagram. Verify B+ and relevant switched supplies at the CAS connector.
- Physically inspect the CAS module for water damage. Remove trim as needed to access the module, check for corrosion or moisture at the connector and housing.
- Measure CAN termination at the OBD port with the network asleep: approximately 60 ohms on a healthy bus.
Resolution
Correct the power, wiring, or module problem identified. For battery replacement, register the new battery via ISTA or a capable aftermarket tool. CAS replacement is not a simple swap: the CAS, DME, and at least one key must be synchronized, which requires specialist equipment. For CAS programming, use ISTA with the correct dataset. Clear all fault memory and verify a complete start cycle multiple times after repair.
2DDA / P3212, U111E Plausibility / signal error
The DME receives CAS messages but either the terminal status message is missing from the expected set, or the data content is outside the plausible range. The detection window is approximately 500 ms. CAS is generally online but its messaging is incomplete or inconsistent.
Symptoms (4)
- Engine may start and run, then stall after a short period.
- Intermittent no-start.
- Warning lights or drivetrain/immobilizer messages.
- Key recognition may work but start authorization fails.
Common Causes (4)
- CAS module partial failure after a voltage event. Certain internal functions degraded but the module still communicates.
- CAS to DME synchronization lost after a DME, CAS, or key replacement without correct pairing.
- Terminal-status signal path issue: KL50 (start) or KL15 (ignition) wiring or relay problems.
- CAS software fault from an interrupted coding or programming session.
Diagnosis Steps (4)
- Read CAS fault memory. Look for terminal-status, ELV (electric steering lock), immobilizer, or internal CAS codes pointing to the specific subsystem.
- Check for recent key, DME, or CAS work. A synchronization mismatch produces plausibility-type faults. Run the CAS-DME synchronization procedure in ISTA if applicable.
- Verify battery and charging: marginal voltage events cause CAS partial failures.
- Review any aftermarket electrical modifications that tap into ignition-switched wiring (alarms, remote starters, dashcams), as these can corrupt terminal-status signaling.
Resolution
Re-synchronize CAS and DME if keys or modules have been changed. Replace a failing relay, correct aftermarket wiring issues, or replace a partially failed CAS module via qualified repair or ISTA programming. For CAS-DME synchronization, follow the ISTA service function exactly: partial or aborted procedures can leave the vehicle in a worse state. Clear codes on DME and CAS and verify multiple successful start cycles.
2DDA / U111F Alive counter / checksum error
The DME receives the CAS terminal-status message but the embedded alive counter or checksum is invalid. The detection window is approximately 200 ms, tighter than the plausibility check because terminal-status integrity is critical for engine authorization. Indicates bus-level corruption or a CAS transmitter-side integrity fault.
Symptoms (4)
- Intermittent start issues.
- Warning lights cycling on and off.
- Often accompanied by other modules reporting integrity errors if the cause is bus-level.
- Can worsen with electrical load or temperature.
Common Causes (4)
- Bus-level corruption from damaged CAN wiring or a bad ground reference on CAS or DME.
- CAS internal transmitter fault from partial electronics failure.
- Poor connection at CAS or DME connector.
- Interference from aftermarket electrical modifications.
Diagnosis Steps (4)
- Check whether other modules log checksum or alive-counter errors referencing CAS. Bus-level corruption usually produces multiple integrity faults across multiple receiving modules.
- Measure CAN termination and inspect wiring: approximately 60 ohms at the OBD port with the network asleep. Inspect for damage.
- Check CAS and DME ground paths. A bad ground on either end is a classic cause of checksum errors.
- Audit aftermarket electrical installs that may be injecting noise onto the bus. Inspect the CAS connector for pushed pins, corrosion, or water damage.
Resolution
Repair the wiring, grounding, or connector fault identified. If the issue is clearly inside the CAS module (no bus-level cause found, no other modules affected), the CAS needs repair or replacement, which requires CAS-DME synchronization and proper programming. Clear codes after repair and verify over multiple drive cycles and electrical loads.