P233BFuel Pressure Regulator C Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P233B points to the ground side of fuel pressure regulator C: the line between valve and low-side driver has contact with ground. In GM's 2025 diesel table 25OBDG04B, regulator C is the second fuel metering unit valve, and the ECM checks this line while the driver is switched off. If the voltage there is too low, meaning less than about 0.5 Ohm towards ground, the sample counts as failed; sampling runs at 100 ms with more than 11 V supply and the engine not cranking, and the code is Type A with the MIL in the first trip. A grounded low-side line can energise the valve permanently, so pump delivery no longer follows the command. GM bulletin 21-NA-149 names P233B for the 3.0L LM2 diesel after harness chafing. The open-circuit test is P233A, the opposite short P233C.
- What you may notice
- Check engine light on immediately
- Rail pressure too high or unstable, rough running
- Reduced engine power possible
- Likely causes
- LikelyInsulation of the control wire worn through against engine or bracket
- PossibleMoisture or corrosion bridging pins in the valve connector
- PossibleMetering valve winding shorted to its housing
- RareLow-side driver in the engine control module damaged
- 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: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.