P26CD: Engine Coolant Pump Control Circuit High

P26CD is set when the control circuit of the engine coolant pump shows a higher voltage than the commanded state allows, for example while the driver is switched off. No manufacturer documents this code in public. CARB's OBD rule asks for output components to be monitored for circuit faults, and the same pump circuit is known from its low-side partner P26CC, which Honda documents on its hybrids in bulletin 25-020. Typical high faults are a control wire touching battery voltage, a relay whose contacts weld shut so the pump keeps running, or an open ground on the pump side. Depending on design the pump then runs permanently or cannot be regulated; the engine module usually stores the code at once and lights the MIL, while warm-up may take longer.

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 lamp on
Pump running after the engine is switched off
Longer warm-up phase

Most likely causes

Pump control wire shorted to battery voltage
Pump relay contacts stuck closed
Open ground at the pump pulling the circuit high

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 P26CD means

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

Frequently asked questions

Can I keep driving with code P26CD?

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 P26CD?

The most common causes are: pump control wire shorted to battery voltage; pump relay contacts stuck closed; open ground at the pump pulling the circuit high.

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.