Powertrain, generic (extended)

P2B98 Exhaust Pressure Control Valve A Supply Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2B98 says the motor of exhaust pressure control valve A is not getting enough supply voltage. On GM's 3.0-litre Duramax, whose 2025 table 25OBDG04B documents the code, the H-bridge that drives the exhaust flap reports undervoltage below 6 V; 240 failed out of 300 samples taken every 12.5 ms set it, outside cranking and with the powertrain relay delivering more than 11 V. Type A, MIL after one trip. Because the main relay is fine in that case, the loss lies further on: a fuse, the feed wire, the connector or a weak ground of the driver. GM bulletin 21-NA-149 lists P2B98 among codes that chafed engine harnesses and blown fuses caused on 2019–2021 trucks, the 3.0 l LM2 included. Without power the flap stays put, so warm-up and back-pressure control suffer. P2B99 is the overheating driver.

Likely causes

Blown fuse or interrupted feed to the valve actuator
Engine harness chafed and shorted (GM 21-NA-149)
Corroded connector or poor ground at the actuator
Weak battery or charging fault causing voltage dips

Symptoms

  • Check engine light after one drive
  • Exhaust flap without function, slower warm-up
  • Further codes for the same fuse or harness

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€30–600
Time0.5–3 h

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

Parts involved

exhaust pressure control valve awiring harness

Related codes

P2B97P2B99P0475P0477

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