29CC

What the Code Means

29CC logs misfires in several cylinders at once. When misfires are spread across different cylinders, the cause rarely lies in a single coil or plug: more often a shared component that controls ignition is at fault.

The telling case is when the ignition components — coils and plugs — have already been replaced and the code comes back. That points to an internal fault in the engine control unit (DME): its ignition driver circuits fail and fire the spark unevenly across cylinders.

Symptoms

• rough idle;
• engine shaking at startup;
• check engine light (EML) on;
• power loss under load;
• cylinder shutdown or limp-home mode.

Diagnosis and Repair

1. Connect ISTA and confirm the misfire codes, noting which cylinders they register on.
2. Bench-test the DME ignition outputs to verify the ignition driver circuits are faulty.
3. Replace the faulty ignition driver circuits.
4. Reinstall the DME and clear the codes. No coding is required after the repair.

The common diagnostic mistake is replacing the plugs and coils again. If the ignition components have already been changed and code 29CC persists, testing the DME is mandatory.

Secondary Problems

• unburned fuel reaches the exhaust and damages the catalytic converter;
• increased fuel consumption;
• with prolonged misfires, potential engine damage.

Don't put off the repair: the fallout hits expensive exhaust-system and engine components.