P2B99 code meaning
Exhaust Pressure Control Valve A Driver Current/Temperature Too High
Powertrain system Generic code P2Bxx codes Check engine light
What P2B99 means
P2B99 reports that the output stage driving exhaust pressure control valve A is running too hot or carrying too much current. In GM's 2025 diesel table 25OBDG04B for the 3.0-litre Duramax, the H-bridge driver temperature has to exceed 170 °C in 240 of 300 samples at 12.5 ms intervals, outside cranking and with more than 11 V on the powertrain relay; Type A, one trip. GM names internal faults of the valve motor as a typical cause, for example shorted windings or a flap that binds so the motor stalls under load. A harness short can overload the driver as well; bulletin 21-NA-149 lists P2B99 on 2019–2021 trucks with the 3.0 l LM2 and chafed engine wiring. The driver then usually shuts down to protect itself and the flap is left uncontrolled. P2B98 is the supply fault, P2B97 the learn fault.
P2B99 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2B99
- Check engine light after one drive
- Exhaust flap no longer controlled
- Possibly reduced power or longer warm-up
Common causes of P2B99
- Most likelyValve motor with internal fault such as shorted windings
- PossibleFlap binding from soot or corrosion so the motor stalls
- PossibleShort in the actuator wiring (GM 21-NA-149)
- Less likelyDefective driver stage in the control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Exhaust pressure control valve aECM
What each part of P2B99 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. |
| 99 | The exact fault in that area. |
What to do next
- Note P2B99 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 P2B99
What does P2B99 mean?
P2B99 means "Exhaust Pressure Control Valve A Driver Current/Temperature Too High". P2B99 reports that the output stage driving exhaust pressure control valve A is running too hot or carrying too much current. It is a generic code, so it means the same on every make.
Is it safe to drive with P2B99?
Drive gently and only to a workshop. With P2B99 the car can go into limp mode (reduced power) to protect itself.
Will P2B99 fail an emissions test?
Yes, it can. P2B99 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2B99 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P2B99 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.