Mercedes-Benz A-Klasse W168
Weaknesses, engine ratings and buying advice
Generations
Engine Overview
The Mercedes-Benz A-Klasse W168 is available with 6 engine variants — from 60 to 140 hp.
First Mercedes passenger car diesel with common rail injection. Modest power but economical. Typical weakness: injectors and glow plug system.
- !! Injectors Leaking — Copper Sealing Ring Failed from 120,000 km
The copper sealing ring between injector and cylinder head fails and allows combustion gases to escape. A tarry black sludge forms around the injectors. If ignored the injector will break on removal.
Symptoms: Diesel smell inside the vehicle, rough idle, black tar-like deposits on the engine block around the injectors, three-cylinder running - !! Seized Injectors on Removal from 150,000 km
Corrosion and tar deposits can cause injectors to seize in the cylinder head. If an injector breaks during removal, extensive cylinder head work is required. Special tools and experience are essential.
Symptoms: Seized injectors discovered during workshop inspection — no driver indication beforehand, only apparent during repair - !! Timing Chain Stretches — Engine Damage Possible from 150,000 km
The K9K-based OM668 in the Citan is prone to premature timing chain stretch. Multiple cases of chain failure and total engine loss documented. Clicking on cold start is an early warning signal.
Symptoms: Clicking or rattling on cold start, noise from front of engine, CEL, in extreme cases engine stall
+ 3 more engine weaknesses + vehicle weaknesses
First Mercedes passenger car diesel with common rail injection. Modest power but economical. Typical weakness: injectors and glow plug system.
- !! Injectors Leaking — Copper Sealing Ring Failed from 120,000 km
The copper sealing ring between injector and cylinder head fails and allows combustion gases to escape. A tarry black sludge forms around the injectors. If ignored the injector will break on removal.
Symptoms: Diesel smell inside the vehicle, rough idle, black tar-like deposits on the engine block around the injectors, three-cylinder running - !! Seized Injectors on Removal from 150,000 km
Corrosion and tar deposits can cause injectors to seize in the cylinder head. If an injector breaks during removal, extensive cylinder head work is required. Special tools and experience are essential.
Symptoms: Seized injectors discovered during workshop inspection — no driver indication beforehand, only apparent during repair - !! Timing Chain Stretches — Engine Damage Possible from 150,000 km
The K9K-based OM668 in the Citan is prone to premature timing chain stretch. Multiple cases of chain failure and total engine loss documented. Clicking on cold start is an early warning signal.
Symptoms: Clicking or rattling on cold start, noise from front of engine, CEL, in extreme cases engine stall
+ 3 more engine weaknesses + vehicle weaknesses
Sandwich construction with the engine mounted below the floor. Robust with proper maintenance but sensitive to oil starvation. A-Class-specific, no successors.
- !! Timing Chain Wears Prematurely from 90,000 km
The single-row roller chain on the M166 can stretch from as early as 80,000–100,000 km. In the worst case the chain breaks and causes severe engine damage. Rattling on cold start is the first warning sign.
Symptoms: Rattling on cold start, rough engine running from altered timing, in extreme cases chain break with total engine damage - !! Oil Creeping in Wiring Harness Damages ECU from 150,000 km
Oil migrates by capillary action into the wiring harness and reaches the engine control unit over years. The ECU corrodes and eventually fails — a typical late failure on high-mileage W168.
Symptoms: Engine misfires, starting problems, fault codes without clear cause, ECU no longer responds to diagnosis - !! Crankshaft Sensor Fails — Engine Dies Suddenly from 130,000 km
The crankshaft position sensor on the M166 in the W168 fails due to oil crust and ageing. Without a signal from the sensor, engine start is impossible. Failure often occurs suddenly.
Symptoms: Engine dies suddenly while driving, starts briefly and dies again, crankshaft sensor fault code, CEL
+ 4 more engine weaknesses + vehicle weaknesses
Sandwich construction with the engine mounted below the floor. Robust with proper maintenance but sensitive to oil starvation. A-Class-specific, no successors.
- !! Timing Chain Wears Prematurely from 90,000 km
The single-row roller chain on the M166 can stretch from as early as 80,000–100,000 km. In the worst case the chain breaks and causes severe engine damage. Rattling on cold start is the first warning sign.
Symptoms: Rattling on cold start, rough engine running from altered timing, in extreme cases chain break with total engine damage - !! Oil Creeping in Wiring Harness Damages ECU from 150,000 km
Oil migrates by capillary action into the wiring harness and reaches the engine control unit over years. The ECU corrodes and eventually fails — a typical late failure on high-mileage W168.
Symptoms: Engine misfires, starting problems, fault codes without clear cause, ECU no longer responds to diagnosis - !! Crankshaft Sensor Fails — Engine Dies Suddenly from 130,000 km
The crankshaft position sensor on the M166 in the W168 fails due to oil crust and ageing. Without a signal from the sensor, engine start is impossible. Failure often occurs suddenly.
Symptoms: Engine dies suddenly while driving, starts briefly and dies again, crankshaft sensor fault code, CEL
+ 4 more engine weaknesses + vehicle weaknesses
Sandwich construction with the engine mounted below the floor. Robust with proper maintenance but sensitive to oil starvation. A-Class-specific, no successors.
- !! Timing Chain Wears Prematurely from 90,000 km
The single-row roller chain on the M166 can stretch from as early as 80,000–100,000 km. In the worst case the chain breaks and causes severe engine damage. Rattling on cold start is the first warning sign.
Symptoms: Rattling on cold start, rough engine running from altered timing, in extreme cases chain break with total engine damage - !! Oil Creeping in Wiring Harness Damages ECU from 150,000 km
Oil migrates by capillary action into the wiring harness and reaches the engine control unit over years. The ECU corrodes and eventually fails — a typical late failure on high-mileage W168.
Symptoms: Engine misfires, starting problems, fault codes without clear cause, ECU no longer responds to diagnosis - !! Crankshaft Sensor Fails — Engine Dies Suddenly from 130,000 km
The crankshaft position sensor on the M166 in the W168 fails due to oil crust and ageing. Without a signal from the sensor, engine start is impossible. Failure often occurs suddenly.
Symptoms: Engine dies suddenly while driving, starts briefly and dies again, crankshaft sensor fault code, CEL
+ 4 more engine weaknesses + vehicle weaknesses
Sandwich construction with the engine mounted below the floor. Robust with proper maintenance but sensitive to oil starvation. A-Class-specific, no successors.
- !! Timing Chain Wears Prematurely from 90,000 km
The single-row roller chain on the M166 can stretch from as early as 80,000–100,000 km. In the worst case the chain breaks and causes severe engine damage. Rattling on cold start is the first warning sign.
Symptoms: Rattling on cold start, rough engine running from altered timing, in extreme cases chain break with total engine damage - !! Oil Creeping in Wiring Harness Damages ECU from 150,000 km
Oil migrates by capillary action into the wiring harness and reaches the engine control unit over years. The ECU corrodes and eventually fails — a typical late failure on high-mileage W168.
Symptoms: Engine misfires, starting problems, fault codes without clear cause, ECU no longer responds to diagnosis - !! Crankshaft Sensor Fails — Engine Dies Suddenly from 130,000 km
The crankshaft position sensor on the M166 in the W168 fails due to oil crust and ageing. Without a signal from the sensor, engine start is impossible. Failure often occurs suddenly.
Symptoms: Engine dies suddenly while driving, starts briefly and dies again, crankshaft sensor fault code, CEL
+ 4 more engine weaknesses + vehicle weaknesses
Vehicle Weaknesses
| Weakness | Cost | |
|---|---|---|
| Sills and Underbody Perforated by Rust Water collects between wheel arch liner and sill, keeping it permanently damp. Extensive through-rusting of side sills including structural damage. Older examples regularly severely affected. Symptoms: Rust bubbles on outer sill surface, creaking when getting in, visible rust under rear doors from 100,000 km | Medium | |
| Rust on Rear Wheel Arches Rear wheel arches rust extensively, sometimes with risk of perforation. Door sills and tailgate also frequently affected. Vehicles over approximately 8 years without regular care are severely at risk. Symptoms: Rust bubbles at inner wheel arch edge, visible rust at door sill from 110,000 km | Medium | |
| Rust damage to door hinges Door hinges rust from the inside out and can break, causing the door to sag and requiring lifting to close properly. Particularly on vehicles without regular underbody maintenance. Symptoms: Door hangs out of alignment, can only be closed properly by lifting, visible rust on hinge from 120,000 km | Low |
Test Reports
TÜV Report 2024
The first A-Class generation shows clearly elevated fault rates in old age, above the class average.
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Known Problems and Issues +
A total of 21 weaknesses have been documented for the Mercedes-Benz A-Klasse W168 (1997–2004) — 13 engine-related and 8 vehicle-related. 2 problem engines: M166 (1.4-2.1L NA), OM668 (1.7L Diesel). Typical issues affect Rust, Gearbox, Suspension, Electronics.
A-Klasse (OM668, 1998–2001) — Stay Away!: Injectors Leaking — Copper Sealing Ring Failed, Seized Injectors on Removal, Timing Chain Stretches — Engine Damage Possible. Power: 60 PS.
A-Klasse (OM668, 1998–2001) — Stay Away!: Injectors Leaking — Copper Sealing Ring Failed, Seized Injectors on Removal, Timing Chain Stretches — Engine Damage Possible. Power: 90–95 PS.
A-Klasse (OM668, 2001–2004) — Stay Away!: Injectors Leaking — Copper Sealing Ring Failed, Seized Injectors on Removal, Timing Chain Stretches — Engine Damage Possible. Power: 75 PS.
A-Klasse (M166, 1997–2004) — Stay Away!: Timing Chain Wears Prematurely, Oil Creeping in Wiring Harness Damages ECU, Crankshaft Sensor Fails — Engine Dies Suddenly. Power: 82 PS.
A-Klasse (M166, 1997–2004) — Stay Away!: Timing Chain Wears Prematurely, Oil Creeping in Wiring Harness Damages ECU, Crankshaft Sensor Fails — Engine Dies Suddenly. Power: 102 PS.
A-Klasse (M166, 1999–2004) — Stay Away!: Timing Chain Wears Prematurely, Oil Creeping in Wiring Harness Damages ECU, Crankshaft Sensor Fails — Engine Dies Suddenly. Power: 125 PS.
A-Klasse (M166, 2001–2004) — Stay Away!: Timing Chain Wears Prematurely, Oil Creeping in Wiring Harness Damages ECU, Crankshaft Sensor Fails — Engine Dies Suddenly. Power: 136–140 PS.
What to watch out for with the Mercedes-Benz A-Klasse? See the detailed listing of all engine and vehicle weaknesses in the sections above.
Frequently Asked Questions
What problems and weaknesses does the Mercedes-Benz A-Klasse W168 have? +
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Which engine is recommended? +
Which Mercedes-Benz A-Klasse W168 engine is the most fun? +
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Last updated: February 2026 · All information without guarantee