P0E7B: Coolant Bypass Valve B Control Circuit/Open
What to do
Expect reduced power under sustained load, or in cold weather a car that feels flat until it has been driven a long way. It is drivable. Say whether the symptoms are worse hot or cold — that single detail points at which position the valve is stuck in and saves real diagnostic time.
What this code means
One of the coolant bypass valves is faulty.
A bypass valve does not route coolant to a different place — it routes coolant past one, and that distinction is what makes this family worth reading carefully.
An electric car's thermal system has several heat exchangers: a radiator to reject heat to the air, a chiller that borrows the air conditioning circuit to cool the battery harder than air can, and a heater for warming it. A bypass valve decides whether coolant flows through one of those or around it.
Which means the failure is usually about efficiency and warm-up rather than about overheating. A bypass stuck open sends coolant round the radiator permanently, so the pack and the electronics never shed heat properly — and that shows up as reduced power on a long climb rather than as a temperature warning. A bypass stuck closed forces coolant through a radiator that is not wanted, so in winter the pack never warms, which is the P0E12 pattern: reduced range, weak regeneration and slow rapid charging on a car whose cooling works perfectly.
Note this family runs six variants, which is the widest in the corpus — four circuit codes plus two mechanical ones. The two mechanical variants are the reason the family exists: a valve fails by sticking, and no electrical test can see that. Stuck/Open and Stuck Closed are the codes that catch it.
The control circuit is open — no drive reaching the valve.
Likely causes
Start here
- Faulty battery pack coolant control valve · specialist
- Corroded or loose connector · specialist
Less common
- Open circuit in control wiring · specialist
- Control module driver failure · specialist
- Faulty inverter coolant pump · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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