2015 Corvette P023F — Fuel Pump Diagnostic and Replacement

Corvette P023F Fuel Pump Diagnostic and Replacement

If you pulled a P023F — Fuel Pump Secondary Circuit/Open on a C7 or C8 Corvette, you are dealing with one of the more misunderstood fuel system architectures in modern GM performance vehicles. The LT1, LT2, and LT4 engines use a dual-pump, direct injection fuel system that behaves nothing like the returnless systems most techs grew up on. Before you throw a pump at it or start chasing your tail, you need to understand how this system is actually designed to work. That understanding is what separates a clean ticket from a comeback.

Understanding the Dual Fuel Pump System

The C7 and C8 Corvette fuel system has two pumps working together, and they serve completely different purposes.

The In-Tank Low-Pressure Pump

The in-tank pump is an electric, variable-speed pump that draws fuel from the tank and delivers it to the high-pressure pump at low pressure — typically 58 to 87 psi depending on demand. This is not a fixed-pressure system. The ECM commands the Fuel Pump Control Module (FPCM) to vary pump speed based on engine load, fuel temperature, and high-pressure pump demand. Speed is controlled through a pulse-width modulated (PWM) signal from the FPCM to the pump.

The High-Pressure Direct Injection Pump

The high-pressure pump is a cam-driven mechanical pump that takes the low-pressure supply from the in-tank pump and builds it to 2,000 to 2,900 psi for direct injection at the fuel rail. The high-pressure pump is not electrically controlled — it is mechanically driven off a dedicated lobe on the camshaft. If low-pressure supply is inadequate, the high-pressure pump cannot build proper rail pressure, and the engine will show fuel trim, power, and starting complaints alongside fuel pressure DTCs.

The Fuel Pump Control Module (FPCM)

The FPCM is the brain of the low-pressure side. It sits outside the tank, typically located at the rear of the vehicle near the fuel tank on C7 models. The ECM communicates with the FPCM over a dedicated serial data line and sends a fuel pump enable signal. The FPCM then generates the PWM output signal to vary pump speed. This two-module communication path is exactly why P023F exists as a separate code from simpler fuel pump circuit codes — the fault can be in the wiring from the ECM to the FPCM, inside the FPCM itself, or between the FPCM and the pump.

What P023F Actually Means

P023F — Fuel Pump Secondary Circuit/Open — indicates the ECM has detected a fault in the circuit between the FPCM and the low-pressure in-tank fuel pump. The word "secondary" here refers to the output side of the FPCM — the driver circuit that actually powers the pump motor. An "open" condition means the ECM or FPCM detected no current flow in a circuit that should have current present when the pump is commanded on.

This code will set when:

• The FPCM commands the pump on and detects no current draw from the pump motor
• There is an open in the wiring between the FPCM and the in-tank pump connector
• The in-tank pump motor has failed internally (open winding)
• The FPCM output driver has failed internally
• There is a connector or terminal integrity issue at the fuel sender/pump module

Related Codes to Watch For

P023F rarely shows up alone on a clean vehicle. These related codes should shape your diagnostic approach:

• P0230 — Fuel Pump Primary Circuit: Fault on the supply or enable side of the FPCM — power feed or control signal from the ECM to the FPCM.
• P0231 — Fuel Pump Secondary Circuit Low: FPCM output is low when it should be high — possible short to ground between FPCM and pump.
• P0232 — Fuel Pump Secondary Circuit High: FPCM output is high when it should be low — possible short to voltage.
• P228D — Fuel Pressure Regulator 1 Performance: High-pressure side is not meeting commanded rail pressure. If P023F is also present, low-pressure supply starvation is the likely root cause of P228D.

If you have both P023F and P228D, fix the low-pressure circuit first. Do not waste time on the high-pressure system when the supply pump is the proven fault.

Root Causes — Most Likely to Least Likely

Based on what actually fails in the field, here is the order you should work through:

1. Fuel pump relay failure: The FPCM is powered through the fuel pump relay in the underhood fuse block. A failing relay can cause intermittent no-start and P023F. Always verify relay operation and swap the relay first — it costs nothing to rule out.
2. Wiring harness damage or connector corrosion: The harness running from the FPCM to the top of the fuel tank module is exposed to road debris and moisture. Rodent damage, chafing at the tank cradle, and corroded connector terminals at the pump module are common. This is especially true on higher-mileage C7s that live in salt-belt states.
3. FPCM failure: The module itself can fail internally. Its output driver circuit is a known failure point, particularly on early C7 production years. When the FPCM fails, you will typically see P023F or P0231 with no other circuit faults and verified good power and ground at the FPCM.
4. In-tank pump module failure: Actual pump motor failure — internal open winding — is less common than the above causes but does happen. High-mileage vehicles, vehicles that have repeatedly run low on fuel, or vehicles that sat for extended periods with degraded fuel are higher risk.

Diagnostic Procedure — Step by Step

Step 1: Verify the Complaint and Pull Codes

Confirm whether the vehicle has a no-start, extended crank, stall, or power concern. Note whether P023F is current or history. A history code with no current complaint changes the diagnostic path — you are looking for an intermittent condition, and voltage drop testing under load becomes more important.

Step 2: Check Power and Ground at the FPCM

Before touching the fuel system, verify the FPCM has good power and ground. With a DVOM, check for battery voltage at the FPCM power supply circuit with the ignition on. Ground should be within 0.1V of chassis ground. A voltage drop greater than 0.5V on either the power or ground circuit is a fault that must be corrected before condemning the FPCM or pump.

Use a quality DVOM or a lab scope if you have one available. Do not skip this step — a module starved for voltage will set circuit codes that look like hardware failure.

Step 3: Verify Low-Pressure Fuel Pressure with a Gauge

Connect a fuel pressure gauge to the Schrader valve on the low-pressure fuel line. On LT1 and LT2 engines, the test port is accessible without dropping the tank. Crank or start the engine and monitor low-pressure supply:

• At idle: 58 to 72 psi
• At wide-open throttle simulation (command via scan tool if equipped): 72 to 87 psi
• Key on, engine off (residual pressure hold): Should hold above 40 psi for a minimum of 5 minutes

If pressure drops immediately when the key is turned off, suspect the check valve inside the pump module. If pressure builds slowly or not at all, the pump is not operating — go back to FPCM power, ground, and command verification before assuming the pump is bad.

Step 4: Check PWM Command vs. Actual Pump Operation

Using a scan tool that supports enhanced GM data, pull the Fuel Pump Commanded Duty Cycle and compare it to actual fuel pressure behavior. The FPCM should ramp pump speed as commanded duty cycle increases. If duty cycle is being commanded but pressure does not respond, the fault is either in the FPCM output circuit or the pump itself.

A lab scope on the FPCM output wire to the pump will show whether the module is generating the PWM signal. If the PWM signal is present at the FPCM output terminal but the pump is not responding, the fault is between the FPCM and the pump — wiring, connector, or the pump motor internally.

Step 5: Voltage Drop Testing on the Pump Circuit

With the pump running, perform a voltage drop test across the pump power supply circuit and across the ground path. Anything above 0.5V total drop indicates resistance in the circuit. Check terminal integrity at the tank module connector — terminals on these connectors are known to back out or develop high resistance contact points over time. Clean, reseat, or replace terminals before replacing the pump or FPCM.

Step 6: Check Fuel Trim Data Alongside Pressure

On LT-series direct injection engines, fuel trim data does not work the same way it does on port injection engines because the ECM trims rail pressure rather than injector pulse width in some operating conditions. However, long-term fuel trim values that are consistently positive (+5% or greater) while fuel pressure is at the low end of spec suggest the engine is compensating for a lean condition driven by inadequate fuel delivery. This supports a low-pressure supply problem rather than an injector or sensor issue.

If fuel trims are normal and fuel pressure is within spec, look harder at the wiring and connector side — a marginal circuit may set P023F without causing an actual fueling complaint.

Fuel Tank Access on the C7 Corvette

Replacing the in-tank pump module on the C7 is more involved than a typical sedan. The C7 fuel tank sits low in the rear of the vehicle inside a composite cradle structure. You do not drop the entire rear subframe, but you do need to deal with the rear cradle cross-member and exhaust routing to gain clearance for tank removal.

Key Considerations Before You Start

• Depressurize the high-pressure fuel system using the scan tool fuel system depressurization function before disconnecting any lines. High-pressure DI systems hold pressure in the thousands of psi — this is not optional.
• Discharge residual low-pressure line pressure at the Schrader valve with a rag wrapped around the fitting.
• Drain as much fuel as possible from the tank before removal. A full tank on a C7 is heavy and creates a significant spill hazard in a confined space.
• The tank has a plastic top plate that holds the pump module. Use a quality spanner wrench or lock ring tool — the plastic ring is expensive to replace if you damage it with an improvised tool.

Pump Module Orientation

When installing the replacement pump module, alignment marks on the module flange and tank opening must be matched exactly. Incorrect orientation will kink the fuel strainer or position the pump inlet incorrectly, causing immediate starvation at low fuel levels and repeat failures. Confirm the alignment arrow on the module matches the index mark on the tank ring before tightening the lock ring.

Torque the lock ring to specification — typically 41 Nm (30 lb-ft) on C7 applications — in a star pattern to seat the O-ring evenly. A leaking O-ring on a freshly installed pump is an avoidable mistake that will ruin your day.

Replacement Tips That Save Callbacks

Fuel Quality and Tank Contamination

Before you button everything up, inspect the bottom of the tank through the pump opening with a light. If you see sediment, water separation, or varnish buildup, the tank needs to be flushed or replaced. Installing a new pump module into a contaminated tank will destroy the new strainer and pump motor on a short timeline. If the customer has a history of using low-quality fuel or the vehicle sat for a long period, flag this to them before they leave.

Verify FPCM Software

On some C7 model years, GM issued calibration updates for the FPCM that changed pump speed commands and fault thresholds. If you are replacing the FPCM and not the pump, verify the replacement module has current calibration or flash it after installation. A misprogrammed or outdated FPCM can set P023F even with a perfectly good circuit and pump.

Post-Repair Fuel Prime

After reassembly, cycle the ignition key on and off three to five times with a 10-second pause between cycles before cranking. This allows the FPCM to ramp the pump and build low-pressure supply before the high-pressure pump is loaded. Cranking immediately after tank work can cause a hard start and briefly operate the high-pressure pump dry — a condition that shortens its service life.

Clear Codes and Confirm with a Drive Cycle

Clear all DTCs after repair. P023F requires a specific enable condition to run the monitor — key on, engine running, FPCM commanded active. The code will confirm repair within the first drive cycle if conditions are met. Do not release the vehicle on a code clear alone. A short road test with scan tool data monitoring fuel pressure and commanded duty cycle is the only way to confirm the repair held.

Summary

P023F on a C7 or C8 Corvette is a diagnostic problem, not just a parts problem. The dual-pump, direct injection fuel system architecture means the fault can live anywhere from a relay to the FPCM to the pump motor to the wiring connecting them. Start at the relay and work your way to the pump using pressure testing, PWM command verification, and voltage drop testing. Understand the fuel trim and pressure data together — they tell a more complete story than either does alone. When you do get to the pump, respect the tank access procedure on the C7 and do not skip the orientation check on reassembly. A systematic approach on this one is what separates a one-hour clean fix from a multi-day diagnostic rabbit hole.