P00B7: Engine Coolant Flow Low/Performance

What it means

The engine coolant flow is below the expected level or does not perform as expected.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The control module monitors whether coolant is circulating through the engine at the expected rate, using temperature behavior to detect inadequate flow. P00B7 sets when flow appears too low or ineffective, which can occur with a damaged water-pump impeller or a blocked coolant passage.

Common causes

Most likely first.

1. Water pump impeller broken or worn
2. Coolant passage blocked

Symptoms

• Check engine light on
• Engine may overheat
• Temperature gauge may rise or fluctuate
• Cabin heater may blow cool air

How to diagnose it

1. Check freeze-frame data and live coolant temperature for rapid rises or fluctuations that indicate poor circulation.
2. With the engine cold, check coolant level and look for leaks or signs of restricted flow; never open a hot cooling system.
3. Observe cabin-heater output and temperature behavior as the engine warms, since weak or changing heat can accompany low coolant flow.
4. Inspect the water pump for signs of failure and verify pump operation using the manufacturer's procedure.
5. If the pump is functioning, investigate coolant passages for blockage and confirm circulation before returning the vehicle to service.

Common fixes

• Correct low coolant caused by a leak and repair the leak.
• Replace a failed or damaged water pump.
• Remove a confirmed obstruction from a coolant passage.
• Refill and bleed the cooling system using the vehicle manufacturer's procedure.

Can I keep driving?

Do not continue driving if the temperature rises, the warning indicates overheating, or cabin heat suddenly goes cold; stop safely and switch off the engine. Low coolant flow can quickly cause severe engine damage and may trigger limp mode.