Mercedes C-Class Exhaust Rattle Cold — Catalytic Substrate
Mercedes-Benz
C-Class
2007
All
⚡ Quick Summary
Severity Level
Medium
Safe to Drive?
⚠️ Drive with Caution
Safety Impact
Indirect risk — worth monitoring, not urgent
Urgency Level
🟡 Monitor Closely
A rattling from the exhaust on cold startup that disappears when warm on W204 C-Class indicates a broken catalytic converter substrate. The ceramic substrate cracks and rattles until it expands and jams. P0420 may or may not be stored. Cat replacement costs £200-500.
Repair / Solution
No confirmed fixes yet. Share yours below.
⚠️ Wrong Diagnosis?
No commonly reported misdiagnoses for this fault yet. If you have replaced a part that did not fix this Mercedes-Benz C-Class 2007 problem, submit a wrong diagnosis report — it helps other drivers avoid the same costly mistake.
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