What are the common causes of P2B79?

A coolant heater B that does not reach commanded current. A weak coolant heater B element. High resistance in the coolant heater B power or ground circuit. A control module pulse width fault on the coolant heater B output.

Scan all modules and compare the coolant heater B command to actual current. Inspect the coolant heater B power and ground connections. Test the coolant heater B circuit for added resistance. Measure the coolant heater B element resistance against spec. Replace coolant heater B if it cannot reach commanded current. Clear the code and retest.

P2B79

Coolant Heater B Control Circuit Performance

System: Powertrain control (P code)
Lamp: Check Engine Light
Category: Powertrain - Hybrid Propulsion

What it means

P2B79 means Coolant Heater B Control Circuit Performance.

Check these first

A coolant heater B that does not reach commanded current
A weak coolant heater B element
High resistance in the coolant heater B power or ground circuit
A control module pulse width fault on the coolant heater B output

What to do next

Scan all modules and compare the coolant heater B command to actual current
Inspect the coolant heater B power and ground connections
Test the coolant heater B circuit for added resistance
Measure the coolant heater B element resistance against spec
Replace coolant heater B if it cannot reach commanded current
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.