P261B on Mercedes-Benz: How to Diagnose & Fix
Coolant Pump "B" Control Circuit Range/Performance
1 Mercedes-Benz model · 1 documented issue · $600-$2,200 repair
P261B on Mercedes-Benz by model: symptoms, diagnosis and fix
The 3.0L M256 inline-six (GLE 450, AMG GLE 53 on the W167) is prone to oil leaks from the oil filter housing/adapter assembly, which integrates the engine oil cooler with coolant passages, making leaks both oil and coolant related. The M256 also relies on an electric coolant pump and an auxiliary electric water pump that can fail, producing erratic cooling behavior and overheating warnings. Because oil and coolant circuits share the adapter, an internal cooler leak can let coolant migrate into the oil and quickly damage the engine.
Common Symptoms
- oil spots under engine
- coolant loss
- low coolant / overheating warning
- erratic temperature gauge
- oil and coolant mixing
How to Fix
Pressure-test the cooling system and inspect the oil filter housing/adapter and integrated oil cooler for seepage; replace the housing gaskets/seals or the complete adapter as needed and refresh coolant. Test the electric coolant pump(s) and replace failing units. Investigate any coolant-in-oil immediately to prevent bearing damage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Mercedes-Benz M256 oil-filter housing A2561801500OEMMercedes-Benz A2561801500
Confirmed failed M256 oil-filter housing on the cataloged GLE450/GLE53 branch Fitment/availability: The inspected direct U.S. Confirm VIN, installed part/supersession
- Genuine Mercedes-Benz M256 main engine water pump A2562002200OEMMercedes-Benz A2562002200
Confirmed failed main coolant-pump branch on the specifically cataloged M256 GLE450/GLE53 application Fitment/availability: The inspected direct U.S. Confirm VIN, pump
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Sources for this issue (2)
P261B code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P261B mean on a Mercedes-Benz?
P261B stands for "Coolant Pump "B" Control Circuit Range/Performance." This code sets when the engine control module commands the electric (auxiliary) coolant pump "B" but the circuit's behavior or feedback does not match what is expected for the commanded state. Coolant pump "B" is typically an electric auxiliary pump that helps circulate coolant for engine, turbo, hybrid, or A/C-related cooling. A range/performance fault means the pump or its control circuit is responding sluggishly or incorrectly, which risks overheating if coolant is not moving properly. On Mercedes-Benz it is documented across 1 model: GLE.
What are the most common causes of P261B?
The most common causes of P261B are: Failing or seized electric auxiliary coolant pump, Wiring or connector fault in the pump control circuit, Corroded or loose pump connector, Low coolant level or air in the system, Faulty pump relay or power supply, Control module (ECM) driver fault (less common). The specific cause varies by vehicle.
How much does it cost to fix P261B on a Mercedes-Benz?
Published repair estimates on Mercedes-Benz range from $600 to $2,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.