P2B73 code meaning
Coolant Heater A Control Circuit Low
What P2B73 means
P2B73 is the low case on the command circuit of coolant heater A: the commanding module reads the line at or near ground when it expects a higher level. Usual reasons are a chafed wire touching body ground, coolant or water in a connector, or an input in the heater that pulls the line down. Hyundai and Kia patent US11378000B2 shows why the line carries only a request: the heater has its own controller, which switches several sheath elements one by one and protects them. No manufacturer documents P2B73 publicly, and no thresholds are known. Under CARB rules, commanded outputs like this must be watched for circuit faults. The heater then normally stays off; an electrified car may start its engine more often for cabin heat. Open circuit is P2B72, high voltage P2B74.
P2B73 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2B73
- Coolant heater does not switch on, weak cabin heat
- Engine runs more often in the cold (hybrids)
- Fuse for the request circuit may blow repeatedly
Common causes of P2B73
- Most likelyCommand wire chafed through and shorted to ground
- PossibleCoolant or water in the heater connector
- PossibleInput of the heater electronics shorted internally
- Less likelyCommanding module cannot drive the line high
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Coolant heater aWiring harnessECM
What each part of P2B73 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. |
| 73 | The exact fault in that area. |
What to do next
- Note P2B73 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 P2B73
What does P2B73 mean?
P2B73 means "Coolant Heater A Control Circuit Low". P2B73 is the low case on the command circuit of coolant heater A: the commanding module reads the line at or near ground when it expects a higher level. It is a generic code, so it means the same on every make.
Is it safe to drive with P2B73?
P2B73 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P2B73 fail an emissions test?
P2B73 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 P2B73 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P2B73 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.