29DA

What the Code Means

Code 29DA points to a misfire in cylinder 6. The fuel-air mixture in that cylinder isn't igniting properly, or not at all. Misfires can come from a bad spark plug, ignition coil, or injector, and in rare cases from a failed ignition driver in the engine control unit (DME).

BMW's ignition system uses individual coils per cylinder, fired by the DME. When it detects a misfire, the DME cuts fuel to the affected cylinder to protect the catalytic converter.

Symptoms

• Engine: rough idle, vibration and shaking
• Behavior: power loss, hesitation under load
• Indicators: Check Engine Light (CEL) comes on, and the CEL may flash during heavy misfires

Diagnosis and Repair

Step 1: Swap the Coil and Plug

Move the ignition coil and spark plug from cylinder 6 to another cylinder (cylinder 1, for example). If the fault follows to the other cylinder, the coil or plug is bad. If it stays on cylinder 6, the problem is in the wiring, the injector, or the DME.

Step 2: Check the DME Ignition Driver

If the swap doesn't turn up the fault, suspect a failed ignition driver for cylinder 6 in the DME. You'll need a bench test of the ECU with an oscilloscope or dedicated equipment to confirm it.

Step 3: Repair or Replace the DME

Once a bad driver is confirmed, you can repair the control unit (replace the transistors) or swap in a good DME.

Indirect Issues

Ignoring code 29DA can lead to:

• Catalytic converter damage: unburned fuel reaches the exhaust, causing overheating and converter breakdown.
• Oxygen sensor contamination: products of incomplete combustion take out the O2 sensors.
• Worse fuel economy: the DME compensates for misfires by enriching the mixture.

Running with misfires for a long time can drive repair costs up sharply, since the catalytic converter and sensors may need replacement.