Mercedes-Benz A-Class: M260 / M264 Electric Water Pump Bearing and Impeller Failure

The M260 2.0T and M264 engines use an electric auxiliary water pump in addition to the belt-driven main pump. The auxiliary pump is prone to bearing wear and impeller disintegration, causing coolant circulation to be reduced or lost. In some cases plastic impeller fragments enter the cooling circuit and block the coolant radiator or heater matrix. Mercedes-Benz issued TSB LI20.30-P-066839 acknowledging the failure mode. Overheating can result if the fault is not detected quickly, which risks head gasket damage on the 2.0T.

• Coolant temperature gauge rising above normal operating range
• High-pitched whining or grinding noise from rear of engine bay
• Low coolant warning light despite no visible external leak
• Heater output reduced or intermittent (blocked heater matrix from debris)
• EPC or engine warning light with fault codes for coolant pump circuit

1. 1

   Check coolant level and condition (milky or low coolant is a red flag).

2. 2

   With STAR Diagnosis check coolant pump motor current draw.

3. 3

   Inspect for coolant weeping at the auxiliary pump housing on the rear of the engine.

4. 4

   Listen for a high-pitched whine from the pump area on start-up.

Parts involved: Water pump.

$600 to $2,200 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the auxiliary electric water pump ever been replaced or inspected?”
• “Has the car ever shown a high temperature warning or EPC light?”
• “Has coolant ever been topped up outside of a scheduled service?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.