P261B Trouble Code

OBII trouble code P261B stands for :

Coolant Pump “B” Control Circuit Range/Performance


This can be either an electrical or mechanical failure, which regardless has an impact on your cooling system. Symptoms of a P261B code may include:

Malfunction Indicator Light On/ Check Engine


A/C system not functioning properly

Vehicle randomly idling or shutting down

This generic powertrain/engine diagnostic trouble code applies to all OBDII-equipped engines with electric coolant pumps but shows up more often in certain hybrid vehicles by Ford, Honda, Nissan, and Toyota.

In my case, it’s a 2010 Toyota Prius(hybrid vehicle). My car would just shut itself down after driving a range of 7-10 miles. With a check engine, light & yellow triangle displayed on the dash, along with a warning message “CHECK HYBRID SYSTEM“. Sounds serious I thought to myself…. what could possibly be wrong with my car? Proceeding to start the vehicle, it would not start up. A couple of hours later I went back and it started up normally, the warning message and the yellow triangle had disappeared. Check engine light stayed on. The car would then drive just as normal for another 10-mile range, then shut down in a repetitive cycle. I connected my OBDII scanner to the car, and it returned a P261B trouble code.

The Coolant Pump B can usually be found mounted to the front of the engine, or inside the wheel wells. The Coolant Pump is operated by a signal from the Powertrain Control Module (PCM).

The PCM receives inputs to determine when and how long it needs to operate the Coolant Pump. These inputs are voltage signals received from coolant temperature, intake air temperature, engine rpm, and air conditioning system pressure sensors. Once the PCM has received these inputs it can modify the signal to the Coolant Pump.

P261B might typically be set because of electrical issues on the coolant pump’s circuit.

The error code also can be caused by mechanical issues, such as a mechanically stuck impeller on the electrically driven coolant pump. Both electrical and mechanical issues cannot be overlooked in the troubleshooting stage, you are now dealing with an intermittent problem.

Causes for this code to display in your diagnostic reader.

Potential causes for P261B to pop up are:

Open in the circuit to the Coolant Pump – likely

Failed Coolant Pump – inoperative (mechanically or electrically) – likely

Failed PCM – unlikely

DIY diagnostic repair solutions can save you time and money during diagnosis.

Locate the Coolant Pump B (CP-B) on your particular vehicle. This pump is usually found mounted to the front of the engine, on top of the engine, inside the wheel wells, or against the bulkhead. Once located, A good starting point would be to visually inspect the connector and wiring. Look for scraping, rubbing, bare wires, burn spots, or melted plastic. Pull the connector apart and carefully inspect the terminals (the metal parts) inside the connector. See if they look burned or have a green tint indicating corrosion. Use an electrical contact cleaner and a bristle brush to clean off the terminals. Let components dry completely then apply electrical grease where the terminals contact.

Grab your scan tool, clear the diagnostic trouble codes from the memory bank, and see if the P261B code returns. If it does not, then the connections were most likely your problem.

For this particular code, this is the most common area of concern, as are the relays/connections to the relays, with a pump failure second.

If the code does return, we will need to test the pump and the associated circuits. Typically, there are 2 wires at each coolant pump. First, disconnect the harness going to the coolant pump. With a Digital Volt Ohm Meter (DVOM), connect one lead of the meter to one terminal of the pump. Connect the remaining meter lead to the other pump terminal. It should not be open or shorted. Verify the resistance specifications for your particular vehicle. If the pump motor is either open or shorted (infinite resistance or no resistance/0 ohms), replace the coolant pump.

If that test passes, with a DVOM, check to make sure you have 12V to the coolant pump power supply circuit (Red lead to the pump power supply circuit, and black lead to a good ground). With a scan tool that can activate the coolant pump, turn it on the coolant pump. If there are no 12 volts to the pump, repair the wiring from the PCM or relay to the pump, or possibly a bad PCM.

If that’s OK, check to make sure you have good ground at the coolant pump. Connect a test light to a 12V battery positive (red terminal) and touch the other end of the test light to the ground circuit going to the Coolant pump circuit ground. Using the scan tool to actuate the coolant pump, see if the test light comes on each time the scan tool actuates the pump. If the test light does not light up, this would indicate the problem circuit. If it does light up, wiggle the wiring harness going to the pump to see if the test light flickers, indicating an intermittent connection.

If all prior tests have passed and you continue to get a P261B, this would most likely indicate a failed coolant pump, although a failed PCM could not be ruled out until the coolant pump had been replaced. If unsure, seek assistance from a trained automotive diagnostician. PCMs must be programmed, or calibrated to the vehicle in order to be installed correctly.

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