P2B79 code meaning
Coolant Heater B Control Circuit Performance
What P2B79 means
P2B79 says that coolant heater B is wired correctly but does not do what it is told: after a request the expected warming, current or status feedback fails to appear. In layouts with several stages, as in Hyundai and Kia patent US11378000B2, the controller switches the stages individually and shuts them down when outlet or housing surface temperature runs too high – a stage disabled by that protection can look like a performance fault from outside. No manufacturer documents P2B79 publicly. CARB 13 CCR 1968.2 (e)(15.2.2) demands functional checks on output components. Low coolant, trapped air, a weak heating element or an internal fault in the heater electronics are typical causes; the over-temperature code of heater A is P2DA6.
P2B79 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P2B79
- Heating power lower than expected
- Heater outlet temperature rises slowly in live data
- Fault may only appear at low outside temperatures
Common causes of P2B79
- Most likelyLow coolant or trapped air, so protection shuts the stage down
- PossibleHeating element of stage B weak or open
- PossibleInternal fault in the heater electronics for stage B
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Coolant heater bWiring harnessECM
What each part of P2B79 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| B | Area: hybrid propulsion. |
| 79 | The exact fault in that area. |
What to do next
- Note P2B79 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2B79
What does P2B79 mean?
P2B79 means "Coolant Heater B Control Circuit Performance". P2B79 says that coolant heater B is wired correctly but does not do what it is told: after a request the expected warming, current or status feedback fails to appear. It is a generic code, so it means the same on every make.
Is it safe to drive with P2B79?
P2B79 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P2B79 fail an emissions test?
P2B79 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P2B79 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P2B79 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.