Powertrain, generic (extended)

P2B99 Exhaust Pressure Control Valve A Driver Current/Temperature Too High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Valve motor with internal fault such as shorted windings
Flap binding from soot or corrosion so the motor stalls
Short in the actuator wiring (GM 21-NA-149)
Defective driver stage in the control module

Symptoms

  • Check engine light after one drive
  • Exhaust flap no longer controlled
  • Possibly reduced power or longer warm-up

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,800
Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

exhaust pressure control valve aecm

Related codes

P2B98P2B97P0475P0478

References: gsi.ext.gm.com, static.nhtsa.gov.