CDA9

What the Code Means

Code CDA9 logs a CAN network communication fault tied to the A/C request message from the DME. Normally the DME sends the A/C request signal to the IHKA climate control module over the CAN bus, and the air conditioning system's operation is built on that signal.

If the signal doesn't arrive or arrives corrupted, the control module stores the code. Causes are damaged wiring, poor connections at the connectors, or a fault in the DME or IHKA module itself. Severity is classified as moderate.

Symptoms

• The air conditioning doesn't work or works intermittently.
• No communication with the climate control module.
• The Check Engine light is on.

Diagnosis and Repair

1. Read the codes and check CAN bus communication with ISTA — this is the first step, and it shows whether the A/C request message drops out completely or only intermittently.
2. Inspect the CAN wiring for damage and corrosion, especially at the connectors — a bad contact at a connection point is the most common reason for an intermittent fault.
3. Check the ground connections.
4. If CAN communication is fine but the A/C request message is still missing, replace the faulty DME or IHKA module.

A typical diagnostic mistake is replacing the climate control module without checking the wiring and ground: the code is often caused by a contact in the connectors, not by a failed module.

Secondary Problems

• If you ignore the fault, the air conditioning system can fail completely.
• Because the problem sits at the CAN bus level, communication glitches can affect other CAN-dependent systems too — that leads to multiple warning indicators and handling problems.