P26FA: Coolant Pump C Overspeed/Air in System

P26FA flags a coolant pump C that turns far faster than it should – the classic sign of a pump moving air instead of liquid. GM uses the code in the engine module of its diesel calibrations for the pump of the low-temperature coolant loop: in table 20OBDG04 an actual speed of at least 4,500 rpm in 5 of 8 one-second samples sets it, in 25OBDG04A 4 of 5 samples suffice. Both list it as Type B, so the MIL comes on after two trips; the test needs at least 11 V at the powertrain relay and is skipped while the engine cranks. GM bulletin 21-NA-149 names P26FA among many codes caused by a chafed engine harness on Silverado and Escalade models. The first check is coolant level and bleeding; the sister codes P2BA0 (underspeed) and P26F8 (stuck) cover the opposite cases.

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 after two trips
Gurgling from the pump area
Higher charge air temperature and possibly reduced power

Most likely causes

Low coolant level or air left in the low-temperature loop after service
Leak in the loop drawing in air
Chafed engine harness corrupting pump signals
Impeller slipping on its shaft or broken

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 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: easy
It can trigger limp mode.
It affects emissions.

What each character of P26FA means

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

Frequently asked questions

Can I keep driving with code P26FA?

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 P26FA?

The most common causes are: low coolant level or air left in the low-temperature loop after service; leak in the loop drawing in air; chafed engine harness corrupting pump signals.

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.