Powertrain, generic (extended)

P28F7 Exhaust Pressure Too High Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28F7 reports that the pressure in the exhaust of bank 1 is higher than the engine model allows. GM documents it in its 2025 diesel ECM tables (25OBDG04B): the monitor looks at the low-pressure EGR differential pressure and fails above 80 kPa while torque demand exceeds a speed-dependent minimum (around 520 Nm at low engine speed, falling to 20 Nm at high speed), counting 480 failures in 600 samples; it is Type A, MIL on the first trip. GM names the cause as an exhaust throttle valve in the wrong position, for example with the link between its upper and lower shafts broken so the plate can stay shut although the actuated shaft has moved. GM bulletin 21-NA-149 lists P28F7 for the 3.0 L LM2 Duramax. Excess back pressure costs power and fuel and stresses the turbocharger.

Likely causes

Exhaust throttle valve stuck closed or its shaft linkage broken
Exhaust restricted downstream, for example by a heavily loaded particulate filter or damaged pipe
Chafed engine harness disturbing valve control (GM 21-NA-149)
Pressure sensor reading too high without a separate sensor code

Symptoms

  • Check engine light on
  • Reduced engine power
  • Higher fuel consumption and more frequent filter regenerations

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–2,000
Time1–6 h

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

Parts involved

exhaust pressure control valve aexhaust pressure sensor b1particulate filterexhaust system

Related codes

P28F8P28F9P048AP0476P2383P2463

References: gsi.ext.gm.com, static.nhtsa.gov, dieselnet.com, law.cornell.edu.