Powertrain, generic (extended)

P233B Fuel Pressure Regulator C Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Insulation of the control wire worn through against engine or bracket
Moisture or corrosion bridging pins in the valve connector
Metering valve winding shorted to its housing
Low-side driver in the engine control module damaged

Symptoms

  • Check engine light on immediately
  • Rail pressure too high or unstable, rough running
  • Reduced engine power possible

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–3 h

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

Parts involved

fuel pressure regulator chigh pressure fuel pumpwiring harness

Related codes

P233AP233CP2C00P0091P2295

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