P233C: Fuel Pressure Regulator C Control Circuit High

With P233C the ECM sees the control line of fuel pressure regulator C pulled towards battery voltage. GM's 2025 diesel table 25OBDG04B runs this test while the low-side driver of the second metering unit valve is switched on: if the voltage across the driver stays high, the line evidently has a path to power of less than about 0.5 Ohm. The check samples every 100 ms with system voltage above 11 V and is Type A, lighting the MIL in the first trip. Because the driver can then no longer pull current through the coil, the valve stays without power and the ECM loses part of its control over high-pressure delivery; hard starting or reduced power can follow. GM bulletin 21-NA-149 lists the code for the 3.0L LM2 diesel with chafed harnesses. P233B is the ground-short counterpart.

Medium severity. Can I keep driving?Avoid long trips and hard acceleration. If you smell fuel or the car stalls, do not continue.

Symptoms

Check engine light on immediately
Long cranking or no start
Reduced power, sometimes stalling

Most likely causes

Control wire chafed against a battery-fed wire in the harness
Damaged valve connector with pins touching
Shorted turns in the metering valve coil
Low-side driver in the engine control module faulty

What to check, in order

Start with the simplest. You can tick off each step.

Check the pump's fuse, relay, and connector
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Replace the filter if it is due for maintenance
Compare commanded and actual pressure in live data
Measure the pressure with a suitable gauge
Check the sensor and regulator before replacing the pump

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P233C means

P: Powertrain: engine and transmission
2: Generic code: same on every make
3: Ignition and misfires
3C: Specific fault in that system

Frequently asked questions

Can I keep driving with code P233C?

Avoid long trips and hard acceleration. If you smell fuel or the car stalls, do not continue.

What causes code P233C?

The most common causes are: control wire chafed against a battery-fed wire in the harness; damaged valve connector with pins touching; shorted turns in the metering valve coil.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.