Fix P0001: Mechanic’s Solutions That WORKED!

OBD2 code P0001 refers to a “Fuel Volume Regulator Control Circuit/Open,” indicating an issue in the fuel volume control system. This code signals that the vehicle’s computer (ECU) has detected an abnormal voltage reading from the fuel volume regulator control circuit, potentially affecting fuel efficiency and engine performance.

P0001 quick overview

Meaning	P0001: Fuel Volume Regulator Control Circuit/Open
Is it serious?	Yes, it can affect the vehicle’s fuel efficiency and overall performance.
Possible causes	– Faulty fuel volume regulator – Wiring issues in the fuel volume control circuit – Poor electrical connections – Faulty Engine Control Module (ECM)
How to diagnose?	Inspect the fuel volume regulator for any physical damage or failure Check the wiring and connectors for damage or poor connections in the fuel volume control circuit Test the electrical parameters of the fuel volume regulator circuit to identify any abnormalities Evaluate the ECM for any signs of malfunction or miscommunication with the fuel volume control system Perform a hard reset of the vehicle’s computer system to see if the code recurs Use diagnostic tools to monitor live data and pinpoint irregularities

How to fix P0001 – learn from mechanics

I looked into P0001 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: Saab P0001

Vehicle information 1996 Saab 900 SE Turbo 2.0L

Issue + repair history

• MIL light on with stored codes P0001, P0171, P0300B, P1171
• Dealer replaced front O2 sensor and reset light, but issue recurred
• Smoke machine test for vacuum leaks yielded no results
• Grounds at intake manifold cleaned and tightened; NGK spark plugs installed
• Purge valve replaced based on research in Iatn archives
• STFT went up to 25% twice at idle, while O2 sensors stayed fixed at 0.5 volts, setting P0171
• Misfire code has not returned, but P0171 and P1171 persist

Other OBD2 Codes + Test Results

• P0001
• P0171: STFT 25%
• P0300B: Random Misfire
• P1171: Lambda control lean

Mechanic suggestions

• Consider replacing the air mass meter due to high LTFT and no vacuum leaks
• Try unplugging the EGR valve to see its effect on other codes
• Suggests soldering junctions for O2 sensor operation in the harness

Final fix Cut open the harness and soldered the junctions for O2 sensor operation, solving the issue.

Case #2: Mercedes P0001

Vehicle information 1996 Mercedes-Benz SL320 3.2L

Issue + repair history

• Intermittent cut out resembling switching ignition off and on
• One-time OBD code P0001 (not recurrent)
• Voltage on base module fuses and injectors remains stable during cut out
• Replaced plugs, wires, crank sensor, fuel pump relay, and throttle body control

Other OBD2 Codes + Test Results

• No codes found upon inspection

Mechanic suggestions

• Check the condition of the engine wiring harness, especially if it’s biodegradable
• Consider issues with the MAS control unit, fuel pump relay, and overvoltage relay
• Use a genuine MB crank sensor, as aftermarket ones may cause faults without flagging codes
• Crank the engine for an extended period during a no-start condition to potentially reveal a CKP code
• Verify engine speed reading on the scan tool and perform a fuel pressure test to ensure it’s at about 50 psi

Final fix Installed a new mass airflow sensor, which resolved the problem.

Case #3: Ford P0001

Vehicle information 2012 Ford Focus SE 2.0L

Issue + repair history

• Vehicle involved in a front-end collision, followed by body and front-end repairs
• Electric steering inoperative
• Stored OBD codes: P0001, U0300, C102D, U3003, P0715, P0718, P2832
• Repairs include replacing plugs, wires, crank sensor, fuel pump relay, and throttle body control

Other OBD2 Codes + Test Results

• No power steering assist
• Several unrelated OBD codes stored in memory

Mechanic suggestions

• Disconnect battery again to observe which codes return
• Check maxi fuses, power feeds, and grounds, ensuring they’re intact and properly connected
• Inspect the wiring harness for damage, especially around the transmission area
• Perform a hard reset on the computer to evaluate code recurrence
• Examine steering components for internal damage post-collision
• Perform on-demand test of the PSCM and attempt re-calibration of torque angle sensor
• Check fusible links within the positive battery cable for integrity
• Diagnose and repair U0300 DTC before proceeding with power steering system diagnostics
• Ensure proper programming of replaced components, especially the steering gear/PSCM

Final fix Replacing fuel pump relay one more time resolved the issue with P0001.

Diagnostic Step	Brief Explanation
Inspect the fuel volume regulator	Checks for damage or malfunction in the regulator
Check wiring and connectors	Looks for damaged wires or loose connections that could interrupt circuit communication
Test electrical parameters	Measures voltage and resistance to identify issues within the control circuit
Evaluate the Engine Control Module (ECM)	Diagnoses potential ECM problems that could be misinterpreting or sending wrong signals
Perform a computer system reset	Resets the vehicle’s computer to clear transient errors and check if the code returns
Use diagnostic tools for live data monitoring	Helps in pinpointing irregularities by observing the system’s behavior in real-time

In dealing with P0001, a thorough approach is needed to ensure that the root cause is correctly identified and addressed. This may involve detailed inspection and testing of the fuel volume control system and its electrical connections, sometimes requiring specialized diagnostic equipment. Given the technical nature of these tasks, consulting a professional mechanic or a dealership technician is often the best course of action to ensure proper diagnosis and repair.