OBD-II Diagnostic Trouble Code
P0231 — Fuel Pump Secondary Circuit Low
P0231 means the fuel pump secondary circuit voltage is low. The secondary circuit is the high-current feed from the relay to the pump, and low voltage typically means the pump is not receiving power, the feed is open or shorted to ground, or the pump is drawing excessive current. It applies to electric in-tank or lift pumps.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Fuel Pump Secondary Circuit Low
Code
P0231
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
What this means for truckers
P0231 (Fuel Pump Secondary Circuit Low) — secondary pump (rare configuration) circuit shorted to ground.
Before you replace parts — try this first
P0231 on the Fuel system is most often failed fuel pump or lift pump — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Crank-no-start, stalling, low power under load and hard starts. Diesels with electric lift pumps may show low fuel pressure and derate.
Common causes
- CommonFailed fuel pump or lift pump ($300–$1200)
- CommonOpen or corroded power or ground wire to the pump ($100–$400)
- OccasionalFailed fuel pump relay contacts ($30–$150)
- OccasionalBlown fuse ($20–$100)
How to fix
Check voltage and ground at the pump connector while commanded on
When to use: First step
Voltage-drop test the feed and ground
When to use: When voltage is low at the pump
Replace the fuel pump
When to use: When power and ground are good but the pump does not run or draws high current
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0200 — Injector Circuit Malfunction
- → P0201 — Injector Circuit Malfunction - Cylinder 1
- → P0202 — Injector Circuit Malfunction - Cylinder 2
- → P0203 — Injector Circuit Malfunction - Cylinder 3
- → P0204 — Injector Circuit Malfunction - Cylinder 4
Frequently Asked Questions
Can I drive with code P0231?
Drive with caution. P0231 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P0231 on a commercial truck?
Total repair cost ranges $20–$1200 depending on the root cause. The cheapest fix is usually the first one listed below — Failed fuel pump or lift pump — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0231 fail a DOT inspection?
P0231 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0231 and related codes?
P0231 is closely related to: P0200 (Injector Circuit Malfunction), P0201 (Injector Circuit Malfunction - Cylinder 1), P0202 (Injector Circuit Malfunction - Cylinder 2), P0203 (Injector Circuit Malfunction - Cylinder 3). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0231 is set without the companions, the issue is more isolated.
How do I prevent P0231 from coming back after a repair?
For P0231 (Fuel Pump Secondary Circuit Low), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.