Volvo Repair Questions? Ask a Mechanic for Answers ASAP
There may be a few different failures here, but it may be a one fix all. The code to start with is P0234 - engine overboost. This is a turbo related code. What can happen is too much pressure will build up and cause the MAF (mass airflow sensor) to read incorrectly. This incorrect reading can cause the rich/lean codes.
- hoses between the turbo and turbo control valve (may be damaged or restricted)
- failed turbo control valve
- failed boost pressure control valve/servo - check for no contamination/not stuck
- hoses between the intake manifold, pressure control, and turbo may be restricted/damaged
- check the maf sensor for corroded/poor connection
- if you have a multimeter, check the resistance in the turbo control valve terminals 1 and 2 - there should be about 30 Ohms; if not then replace.