Fix P0231: Mechanic’s solutions that WORKED

The OBD2 code P0231, which signifies “Fuel Pump Secondary Circuit Low,” indicates a problem in the electrical circuit associated with the fuel pump’s secondary control circuit. This can lead to issues such as no-start conditions, stalling, and inconsistent fuel delivery, impacting the vehicle’s performance and reliability.

P0231 quick overview

Meaning	P0231: Fuel Pump Secondary Circuit Low
Is it serious?	Yes, as it can prevent the engine from starting or cause it to stall unexpectedly.
Possible causes	– Faulty fuel pump relay or fuse – Wiring issues in the fuel pump circuit – Faulty fuel pump control module – Poor connections or corroded terminals in the circuit
How to diagnose?	Inspect the fuel pump relay and fuse for damage or failure. Check the wiring for shorts, breaks, or corrosion. Evaluate the fuel pump control module for proper operation. Test the fuel pump to ensure it’s receiving power and functioning correctly.

How to fix P0231 – learn from mechanics

I looked into P0231 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Cadillac

Vehicle information 1996 Cadillac Seville SLS 4.6L

Issue + repair history

• Came in as a no-start condition.
• Replaced ignition lock cylinder assembly.
• Engine cranks but does not fire.
• Dash displays “Service Fuel System” message.
• OBD2 code: P0231 (Short in fuel wiring).
• Found small pink wire to the ignition 1 relay rubbed through, resulting in power loss on fuse.

Other OBD2 Codes + Test Results

• P0231: Short in fuel wiring.

Mechanic suggestions

• Check if new keys were coded; dealer may need to do this.
• Corrosion in the relay and fuse block center on the left strut tower could be a potential issue.
• Ensure correct VATS (Vehicle Anti-Theft System) key values are used; wrong keys may result in a security message and no crank.
• If using old keys, check wiring from lock cylinder to the base of the column.
• P0231 indicates a fuel pump relay, fuse, or wiring problem, not a VATS issue.
• Check the fuse and relay; if okay, check for power at the gray wire going to the PCM (Powertrain Control Module); if okay, consider replacing the PCM.

Final fix

• Found small pink wire to the ignition 1 relay rubbed through, causing power loss on fuse.

Case #2: Ford

Vehicle information 2003 Ford F-250 Super Duty XL 5.4L

Issue + repair history

• Came from another shop after fuel pump replacement.
• Problem occurs while cruising; engine stalls, customer pulls over, shuts off the key, and the truck restarts.
• Symptoms include intermittent stalling.
• OBD2 code: P0231 (Fuel pump secondary circuit low) stored.
• No other symptoms observed.
• Wiggled wiring and tapped on the central junction box with no effect.

Other OBD2 Codes + Test Results

• P0231: Fuel pump secondary circuit low.

Mechanic suggestions

• Replace the fuel pump relay, as it could be original and prone to failure.
• Check the inertia switch connector for melting or overheating.
• If the inertia switch connector is okay, replace the fuel pump relay, considering the intermittent nature of the problem.
• Also, check the pump harness for any issues.

Final fix

• Replaced the central junction box (CJB), and the problem seems to be resolved.
• The truck was known for going months before acting up, so long-term observation is necessary.

Case #3: Chevrolet

Vehicle information 2008 Chevrolet Silverado 1500 LT 5.3L

Issue + repair history

• Came in as a no-start condition with no fuel pressure.
• Customer started the truck, put it in reverse, and it died.
• OBD2 code: P0231 (Fuel pump secondary circuit low) stored.
• No fuel pump fuse or relay found in their respective spots.
• Attempted to command the fuel pump on using a Tech2 scanner, but it only allowed increase or decrease, then kicked out because the engine wasn’t running.
• Inspected the flow control module, which appeared okay.
• Removed the driveshaft to access the fuel tank, disconnected electrical, and tested power and ground circuits, which tested good.
• Removed the fuel pump and found that it worked on the bench but wouldn’t put out any fuel.

Other OBD2 Codes + Test Results

• P0231: Fuel pump secondary circuit low
• P069E: Fuel pump control module request MIL
• P0446: Evap vent code
• P1174: Fuel trim cyl balance
• P0573: Brake switch circuit 1 high voltage

Mechanic suggestions

• Check for water intrusion in the fuel pump control module (FPCM), located above the spare tire.
• Follow the diagnostic flowchart for code P0231.
• Check for codes in the FPCM and inspect fuses related to it.
• Investigate corrosion or water damage in the area above the spare tire.
• Check fuses related to the ECM and FSCM in the underhood fuse block.
• Verify injector noid and spark, and replace the fuel pump if necessary.
• Follow diagnostics for code P0231; likely a faulty fuel pump driver module.
• Replace and program a new fuel pump control module if needed.

Final fix

• Replaced the fuel pump, and the truck started working normally.
• The new fuel pump was unusually quiet compared to the old one.

Diagnostic Step	Explanation
Inspect fuel pump relay and fuse	Look for signs of wear or failure that could interrupt power to the pump.
Check wiring	Examine for any damage or corrosion that could impair circuit integrity.
Evaluate fuel pump control module	Ensure it’s operating correctly and hasn’t been damaged by water or wear.
Test fuel pump operation	Confirm the pump is receiving power and is capable of pumping fuel.

Through these service cases, we see a range of solutions from repairing damaged wires to replacing key components like the fuel pump itself or the central junction box. Each fix was guided by thorough diagnostics, highlighting the importance of checking the entire circuit from relays and fuses to the pump and its control module to resolve the underlying cause of P0231 effectively.