P261B: How to Diagnose & Fix — Coolant Pump "B" Control Circuit Range/Performance
5 vehicles · 5 makes · $250-$2,200 repair
How to diagnose and fix P261B: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Toyota Prius · 2010–2015
Unlike a belt-driven pump, the 2ZR-FXE engine coolant pump is a brushless electric unit commanded by duty cycle from the ECM. The internal motor/controller degrades and the pump slows or stops, so coolant stops circulating through the engine. The ECM detects the speed feedback falling below threshold and sets P261B (or P261C), lights the check engine and hybrid warning lights, and will shut the gas engine down to protect it, leaving the car crawling on battery only. Toyota addressed it with T-SB-0143-10 and a revised pump design; it is one of the most-reported repairs on third-gen Prius, Prius v, Prius c and Lexus CT200h.
Common Symptoms
- Check engine light with hybrid system warning
- Engine temperature climbing, overheat message
- No coolant movement visible in the reservoir with engine running
- Gas engine shuts down or car enters limp mode
- Heater blows cold
How to Fix
Confirm with the code plus a visual check of coolant flow in the reservoir with the engine running. Replace the electric engine water pump with the updated Aisin/Toyota unit (do not reuse the old O-ring), refill and run the Techstream/manual air-bleed procedure - trapped air in this system will cause repeat overheat codes and can mimic a second pump failure. It is a 1-2 hour job accessible from the passenger side of the engine. Cheap no-name aftermarket pumps are a common repeat-failure complaint.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Aisin WPT-190 electric engine water pump
replace an engine coolant pump proven slow, electrically faulty or non-operational after circuit diagnosis Fitment/availability: 2010-2015 Prius 1.8L 2ZR-FXE; Aisin also catalogs the branch for 2012-2015 Prius Plug-in and 2012-2018 Prius…
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Sources for this issue (3)
Cadillac CT5 · 2020–2020
GM issued a TSB (December 2020) stating the printed circuit board inside the electric water pump on affected CT4/CT5 vehicles may have been manufactured incorrectly, potentially causing a water pump failure; when this occurs the vehicle displays warnings as coolant temperatures rise, the oil pressure gauge falsely indicates high oil pressure, a reduced power/torque message appears, and if ignored the AC is disabled and the driver is told to turn off the engine . The 2.0L LSY turbo-four (base engine in the CT5) is one of the engines susceptible to this water pump failure (the other being the 2.7L L3B, which is not used in the CT5) .
Common Symptoms
- High coolant temperature warning
- Oil pressure gauge falsely reading high
- 'Reduced engine power' message
- AC compressor cut out
- 'Turn off engine' chime/message
- No coolant flow at idle
How to Fix
Dealers inspect and, if necessary, replace the entire water pump assembly; the job takes roughly four hours and was performed at no cost to the owner under the Customer Satisfaction Program TSB . The TSB coverage window ran through December 31, 2022, so out-of-warranty owners now face out-of-pocket cost . Independent shop cost for the electric pump assembly typically runs $700–$1,400 parts plus labor. Diagnose by scanning for coolant temp DTCs and observing the false-high oil pressure indication, which is a hallmark of this specific failure mode.
Sources for this issue (1)
BMW 3 Series · 2012–2013
BMW SIB 01 13 21 identifies 2012-2013 E92/E93 335i, 335is and specified xDrive coupe/convertible vehicles with N54T or N55 engines in the electric coolant-pump settlement population. The bulletin provides a diagnosis-and-repair path when a warning or fault is present; it does not support preventive replacement for every 2012-2018 N55 3 Series.
Common Symptoms
- Engine warning lamp
- Engine-overheat warning
- Reduced-power operation may accompany overheating
How to Fix
Stop safely if an overheat warning appears and avoid continued operation until the cooling system is checked. Verify the chassis, engine and VIN, read fault memory and follow the current coolant-pump test plan before replacement. Settlement benefits were time-limited. ShowMeTheParts resolved five 2012 335i water-pump candidates, but fitment does not prove failure or remedy, so no commerce link is approved.
Sources for this issue (1)
Audi A6 · 2005–2023
Mercedes-Benz GLE · 2020–2025
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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?
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.
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?
Repair costs for P261B range from $250 to $2,200, depending on the vehicle and root cause.
Which vehicles are affected by P261B?
Au7o has documented P261B across 5 vehicle models from 5 manufacturers: Audi, BMW, Cadillac, Mercedes-Benz, Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.