Powertrain, generic (extended)

P28F8 Exhaust Pressure Too High Bank 2

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28F8 is the bank 2 twin of P28F7 and only appears on engines whose two cylinder banks have separately measured exhaust paths, such as V engines with one turbocharger or flap per bank. It means the exhaust pressure on that side exceeds the modelled value. No manufacturer documents P28F8 publicly; GM's 2025 diesel tables cover only the bank 1 code on an inline engine, where a stuck exhaust throttle plate caused a reading above 80 kPa under load. By analogy, a bank 2 fault would come from a flap, turbine or pipe restricted on the second side. DieselNet explains that higher back pressure raises fuel use and emissions and hurts performance. CARB requires monitoring of boost and aftertreatment systems for such faults. Comparing both banks helps: if only bank 2 is high, look downstream on that side.

Likely causes

Exhaust flap or throttle on bank 2 stuck closed
Restriction downstream on bank 2, for example a blocked catalyst or filter section
Variable turbine of the bank 2 turbocharger stuck in a closed position

Symptoms

  • Check engine light on
  • Loss of power, possibly with uneven running between banks
  • Increased fuel consumption

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–2,500
Time1–6 h

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

Parts involved

exhaust pressure control valve bexhaust pressure sensor b2particulate filterexhaust system

Related codes

P28F7P28FAP04A5P047AP2465

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