P0231 on GMC: How to Diagnose & Fix
Fuel Pump Secondary Circuit - Low
6 GMC models · 6 documented issues · 2 critical · $300-$1,200 repair
P0231 on GMC by model: symptoms, diagnosis and fix
The GMC Savana (and Chevrolet Express) fuel pump module is known for premature failure between 80,000-140,000 miles, often stranding drivers without warning. The in-tank electric fuel pump motor burns out or the sending unit becomes erratic. Running the tank consistently below 1/4 generates heat that shortens pump life. Commercial use Savanas that frequently run low on fuel — common in fleet operations — see pump failures well before 80,000 miles. The fuel pump is a demanding repair requiring tank removal on the Savana.
Common Symptoms
- Hard start or extended cranking before engine fires
- Engine stalls at idle and won't restart when hot
- Fuel pressure below specification (should be 55-60 psi)
- Engine stumbles and hesitates under load
- No-start condition with no fuel pressure
- Fuel gauge erratic or reads wrong
How to Fix
Replace fuel pump module (ACDelco MU1374 for 6.0L Savana, MU1373 for 4.8L). Keep fuel tank above 1/4 full at all times. For fleet vehicles, replace pump proactively at 100,000 miles. Aftermarket Walbro or Delphi pumps are common alternatives.
Sources for this issue (2)
Gasoline C/K 3500 models use an in-tank electric fuel pump that fails prematurely, often at 80,000-120,000 miles (diesel models use a separate lift pump). The truck's large fuel tank (up to 42 gallons) means the pump works harder to maintain pressure over a longer fuel column. Running the tank below 1/4 regularly accelerates failure because the fuel cools and lubricates the pump — low fuel means less cooling. The dual-tank models are particularly problematic as the fuel switching valve can fail and starve one pump.
Common Symptoms
- Engine stalling or dying at idle
- Hard starting, especially when hot
- Whining noise from fuel tank area
- Engine sputtering under load or going uphill
- Loss of power at high RPM
How to Fix
Replace the fuel pump assembly (includes pump, strainer, and sending unit). Use an AC Delco or Delphi pump for reliability. On dual-tank models, replace the tank selector valve and check valve at the same time. Replace the fuel filter (external, frame-mounted) during the repair. Consider adding a supplemental fuel pressure gauge to monitor pump health.
Sources for this issue (2)
The in-tank fuel pump can fail from heat and debris, the same failure seen on the Chevrolet S-10.
Common Symptoms
- Stalling
- Hard starting
- Loss of power at speed
How to Fix
Confirm low fuel pressure before replacing parts by checking pressure at the Schrader valve on the fuel rail; 1996-and-later 4.3L Vortec trucks typically need about 60-66 psi key-on (1992-1995 4.3L CPI trucks about 55-61 psi) to start and run correctly, while weak pressure, intermittent drop-out, or excessive current draw points to a failing in-tank pump. Inspect the fuel pump relay, fuse, ground at the frame, and the pump electrical connector for heat damage, then replace the complete in-tank fuel pump module/strainer and install a new fuel filter at the same time; on many Sonomas the tank must be lowered, though removing the bed can also improve access on some configurations. Use a quality Delco or Delphi module rather than a pump-only repair, and clean out any tank debris to prevent repeat failure. Typical repair cost is about $400-$800 parts and labor depending on engine, cab/bed configuration, and whether the sending unit harness also needs replacement.
Sources for this issue (2)
A common GMT800 Sierra problem is failure of the in-tank fuel pump module, often from worn pump motors or failed level-sender/module electronics. Owners report long crank, hard starting, loss of power under load, or sudden stall/no-start conditions, especially as mileage climbs. This issue is widely documented in owner forums and complaint databases across 4.3L, 4.8L, 5.3L, and 6.0L trucks.
Common Symptoms
- long crank before starting
- intermittent no-start
- engine stalls while driving
- loss of power on acceleration
- fuel gauge may act erratically if sender/module is failing
- whining noise from fuel tank
How to Fix
Diagnosis usually starts with checking fuel pressure at the rail and verifying pump prime at key-on. Low or unstable pressure, especially after sitting, points to a weak pump or failing module. Repair is replacement of the complete fuel pump module and, ideally, the fuel filter on applicable years; corroded electrical connectors at the tank should also be inspected and replaced if heat-damaged.
Sources for this issue (2)
The in-tank fuel pump in the Suburban's large fuel tank (42 gallons) fails prematurely. Owner and technician reports point to the pump/sender electrical connector inside the tank overheating and arcing, which kills the pump and cuts engine power.
Common Symptoms
- Loss of power at highway speed
- Extended cranking to start
- Engine cuts out under acceleration
- Whining from rear of vehicle
How to Fix
Replace fuel pump module assembly (Delphi FG0100). The large tank makes this job more involved - support the tank properly during removal. Replace the fuel filter (frame-mounted) at the same time.
Sources for this issue (2)
The Safari's electric fuel pump sits inside the gas tank. Owner references say the stock pump is known to fail after about 100,000 miles. It usually doesn't quit all at once. Instead it gets too weak to start or run the van, so you get hard starts, stalling or loss of power under load, even though you can still hear the pump running. Pumps on the later port-injected vans have a harder job: those systems run at about 55-66 psi, far more than throttle-body injection, and enthusiast references say higher system pressure wears the pump out faster. On older vans, ethanol in the fuel can eat away the fuel pulsator (damper) until it leaks. The same reference says 1996 appears to be the last year that used it. Not every no-start or slow start is the pump. On vans through 1998, the pump circuit also runs through the 3-prong oil pressure switch. A bad switch, fuel pump relay or connection can cause long cold-start cranking or no pump prime at key-on.
Common Symptoms
- Hard starting or long cranking
- Stalling
- Loss of power under load
- No fuel pump prime sound at key-on
- Low fuel pressure even though the pump can be heard running
How to Fix
1. Check fuel pressure at the rail with a gauge before replacing any parts. The spec depends on the injection system: - Throttle-body (TBI) vans: about 9-14 psi with the engine running. - 1996-2001 central port (SCPI) vans: 60-66 psi, key on and engine off. - 2002-2005 multiport (MPFI) vans: 55-62 psi, key on and engine off. 2. A weak pump can still be heard running, so the pressure reading is the real test. 3. If the pump doesn't prime at key-on or the van cranks a long time, first check the fuel pump relay, the fuse and the wiring at the tank connector. On 1998 and earlier vans, also check the oil pressure switch (3-prong sender) and its connector, because the pump circuit runs through it. Any of these can mimic a bad pump. 4. If pressure is low and the pump has good power and ground, replace the in-tank pump. - The tank has to be lowered. Run it as low as you can first: a full 27-gallon tank holds about 165 lb of fuel. - Owners recommend ACDelco/Delphi pumps over the parts-store brands. Watch for listings that show ACDelco/Delphi part numbers but sell a lower-quality pump. - Also replace the filter sock on the bottom of the pump and the inline fuel filter, which is under the driver's seat near the frame rail. 5. After installing the pump, confirm both the prime pressure and the running pressure. Cost: an Astro/Safari owner reference says a dealer charges about $900 for the replacement, while a DIY pump replacement costs less than $350.
Sources for this issue (4)
P0231 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0231 mean on a GMC?
P0231 stands for "Fuel Pump Secondary Circuit - Low." This code indicates the engine computer detected a low-voltage condition in the fuel pump's secondary (driver/output) control circuit. Many vehicles control the fuel pump through a relay or a dedicated driver module, and the computer monitors the voltage on that circuit to confirm the pump is being powered correctly. When the feedback voltage stays lower than expected, P0231 sets. Because the fuel pump supplies pressurized fuel to the injectors, this fault can cause hard starting, stalling, or no-start conditions. On GMC it is documented across 6 models: Savana, C/K 3500, Sonoma, Sierra 1500, Suburban, Safari.
What are the most common causes of P0231?
The most common causes of P0231 are: Faulty fuel pump relay, Corroded or loose connector at the pump or relay, Damaged or shorted wiring in the pump power circuit, Poor ground for the fuel pump circuit, Failing fuel pump drawing abnormal current, Faulty fuel pump driver module, PCM/ECM internal driver fault (rare). The specific cause varies by vehicle.
How much does it cost to fix P0231 on a GMC?
Published repair estimates on GMC range from $300 to $1,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.