P28F8Exhaust Pressure Too High Bank 2
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Check engine light on
- Loss of power, possibly with uneven running between banks
- Increased fuel consumption
- Likely causes
- LikelyExhaust flap or throttle on bank 2 stuck closed
- PossibleRestriction downstream on bank 2, for example a blocked catalyst or filter section
- RareVariable turbine of the bank 2 turbocharger stuck in a closed position
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.