2002 MERCEDES-BENZ C-CLASS

Typical onset: 70,000-120,000 mi

Symptoms: Loud rattling or knocking from low in the engine at idle and low RPM, Metal shavings in oil, sometimes glitter-like particles on dipstick, Check engine light with camshaft position correlation codes, Sudden catastrophic failure—engine seizes or timing jumps

Fix: Balance shaft module grenades and sends metal through the entire oiling system. Only real fix is complete engine rebuild or replacement—new pistons, bearings, crank polishing, head work, the whole nine yards. We're talking 25-35 labor hours for a proper rebuild, or 12-16 hours for a used engine swap if you can find a good low-mileage donor.

Estimated cost: $4,500-8,000

Typical onset: 90,000-150,000 mi

Symptoms: Harsh or delayed shifts, especially 2-3 and 3-4 upshifts, Limp mode (stuck in 2nd gear) with transmission codes, Slipping between gears or no movement in drive or reverse, Erratic shifting when transmission is cold, may improve when hot

Fix: The 13-pin connector on the conductor plate corrodes and the circuit board cracks from heat cycling. Trans has to come out or you drop the pan and valve body—either way it's 6-8 hours. Replace conductor plate, 13-pin connector, valve body gaskets, filter, and fluid. Some shops can get away with pan-drop method, but full removal gives you better access to inspect everything.

Estimated cost: $1,800-3,200

Typical onset: 60,000-130,000 mi

Symptoms: Random no-start conditions, especially when engine is hot, Stalling at idle or while driving, restarts after cooling, Extended cranking before engine fires, Check engine light with P0335 (crank sensor) or P0340 (cam sensor) codes

Fix: These sensors fail from heat exposure on the Kompressor engines more than the V6s. Crank sensor is behind the starter on most models—1.5-2 hours. Cam sensors are up top, easier access at 0.8-1.2 hours each. Always replace both when one fails because the second usually follows within 10,000 miles.

Estimated cost: $350-650

Typical onset: 80,000-140,000 mi

Symptoms: Red ATF puddles under engine bay, usually driver's side, Transmission slipping or harsh shifts after fluid loss, Low transmission fluid level on dipstick, Visible fluid seeping from cooler line connections at radiator

Fix: The rubber sections of the hard lines crack and the crimp connections at the radiator fail. You need OEM lines—aftermarket ones leak within a year. Replace both feed and return lines as a set, flush cooler, refill and relearn adaptation. About 2.5-3.5 hours including fluid service.

Estimated cost: $450-750

Typical onset: 70,000-110,000 mi

Symptoms: Clunk or thud when shifting from park to drive or reverse, Excessive vibration at idle, especially with A/C on, Engine rocks visibly when revving in park, Transmission shifter feels notchy or loose

Fix: The hydraulic engine mounts collapse and the transmission mount tears. Front engine mount is 2-2.5 hours, trans mount is 1.5-2 hours. Do them together—if one is shot, the others are stressed. You'll need to support the engine and trans from above or below. Use OEM or Lemforder—cheap mounts fail in 20k miles.

Estimated cost: $650-1,100

Typical onset: 90,000-150,000 mi

Symptoms: Intermittent stumbling or hesitation under acceleration, No-start with whining or silent fuel pump, Fuel gauge reads empty when tank is full, or erratic readings, Engine cuts out at highway speed then restarts

Fix: The in-tank pump assembly wears out and the level sender float arms crack. Tank has to come down—3.5-4.5 hours. Replace the entire pump module, not just the pump, because the sender will fail next. Fuel system needs depressurizing and you'll want to do this when tank is under half full to save your back.

Estimated cost: $800-1,300

Typical onset: 60,000-100,000 mi

Symptoms: Rough idle, surging at steady throttle, Poor fuel economy, running rich (black exhaust), Hesitation or flat spot during acceleration, Check engine light with fuel trim or MAF range codes

Fix: Oil vapors from the PCV system coat the hot-wire elements. Clean it first with MAF-specific cleaner (not carb cleaner)—0.3 hours. If that doesn't fix it, replacement is 0.5 hours. Use OEM Bosch sensors only; pattern parts throw false codes. Also inspect air filter housing for oil contamination and check PCV valve.

Estimated cost: $150-400