P26F6: Coolant Pump C Control Circuit High

P26F6 is stored when the control line of coolant pump C carries a higher voltage than the commanded state allows. In practice that means the wire touches a live circuit, the pump has lost its ground so the line floats up, or the line is open between driver and pump in a way the output stage reads as high. No public service document covers P26F6 itself. The low-side sister P26F5 is documented by Bentley for the auxiliary heater pump of its VW-group V8 models, where internal corrosion and pump self-diagnosis were the causes; CARB requires electric parts serving emission control or other monitors to be checked for such circuit faults. A pump held permanently on may keep running after the engine is switched off and drain the battery; one that cannot start leaves its loop without flow.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

Check engine light on
Pump runs on after switch-off or does not run at all
Weak heater output with the engine idling

Most likely causes

Control wire shorted to battery voltage
Missing or corroded ground at pump C
Internal electronics of the pump failed

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P26F6 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
6: Control modules and outputs
F6: Specific fault in that system

Frequently asked questions

Can I keep driving with code P26F6?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P26F6?

The most common causes are: control wire shorted to battery voltage; missing or corroded ground at pump C; internal electronics of the pump failed.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.