P1671 — Secondary Fuel Pump Relay Control Fault

P1671 — Secondary Fuel Pump Relay Control Fault. P1671 can leave the secondary fuel-pump function unavailable and may reduce fuel-system redundancy.

For Ford vehicles

secondary fuel pump relay

vehicle

Is it safe to drive?

Drive cautiously while the fault is present P1671 can leave the secondary fuel-pump function unavailable and may reduce fuel-system redundancy. Avoid extended travel until the relay circuit is repaired, and stop driving if the engine stalls, fuel pressure becomes abnormal, or a fuel-pump warning appears.

Typical symptoms

The check-engine light or a fuel-system warning remains on
The engine may hesitate, surge, or stall under fuel-demand conditions
The secondary fuel pump may not be heard during the key-on test
Fuel pressure may become inconsistent if the affected pump is required
The relay may remain inactive when commanded by the control module
P1671 may be stored without any noticeable drivability symptom

Common causes

A failed secondary fuel pump relay
An open or high-resistance wire in the relay coil or control circuit
A blown fuse or defective power feed supplying the relay
Corroded relay-socket contacts or a poor relay-side ground
A failed powertrain control module relay-control driver
An incorrect relay or excessive current draw from the secondary fuel pump circuit

How to diagnose with an OBD scanner

Confirm P1671 and capture related data Connect an OBD scanner, ELM327 adapter, or AIScanAuto-compatible tool and read stored, pending, and permanent codes. Save the freeze-frame data, especially engine speed, battery voltage, and operating conditions recorded when P1671 appeared.
Check the relay and its power source Use the vehicle wiring diagram to locate the secondary fuel pump relay. Inspect the relay, socket, connector, and associated fuse for damage, heat, corrosion, or looseness, then confirm that the specified power and ground are present.
Test the relay control circuit With the wiring diagram and service information as guides, measure voltage at the relay coil or control terminal while P1671 is active. Compare the measurement with the specified command state and check for an open circuit, short to power or ground, or excessive voltage drop.
Verify relay operation Test the relay for continuity with a multimeter or substitute a known-good relay of the correct type and pin configuration. If the relay cannot be commanded, note that basic ELM327 and AIScanAuto interfaces generally cannot perform bidirectional relay tests.
Inspect downstream pump wiring carefully Check the secondary pump power and ground paths for damaged insulation, pinched wiring, connector corrosion, and voltage drop under load. Avoid disconnecting pressurized fuel lines; relieve fuel pressure according to the manufacturer procedure first.
Clear and verify the repair Clear the codes with the scanner, operate the vehicle through several load cycles, and confirm that P1671 does not return. If the relay is commanded but the fault remains, test the control-module driver and related ground circuits before replacing the module.

Approximate repair cost

A rough independent-shop estimate is USD 150-650, depending on relay accessibility, whether wiring or a control-module driver is faulty, and regional labor rates. These figures are estimates only, not verified quotes, and costs vary by region, vehicle, and parts availability.

Common questions

What does P1671 specifically identify?

P1671 identifies a fault involving the secondary fuel pump relay or its control circuit. It does not by itself confirm that the relay, wiring, fuse, or control module is the failed part.

Can the vehicle still run with P1671 stored?

Yes, because some vehicles can operate using the primary fuel pump even when the secondary relay circuit has failed. The remaining pump may still lose support during heavy demand, so repair should be prompt.

Will an ELM327 or AIScanAuto tool test the relay?

Most ELM327 and AIScanAuto-compatible tools can read P1671 and related freeze-frame data but cannot command the relay or measure its coil and contact circuits. Those checks generally require wiring information and a multimeter.

Should the relay or the control module be replaced first?

Test the relay, fuse, connectors, power, ground, and control wiring before condemning the module. Replacing the control module without those checks can leave P1671 present and create an unnecessary expense.

P1671 — ---

When your scan tool displays P1671, it tells you that a control unit has detected a signal from a sensor or actuator falling outside its factory-calibrated operating range. The specific fault description reads "---," placing this code in the broader category of vehicle electronics faults. Essentially, a circuit that should behave predictably is now behaving erratically — either sending no signal, the wrong signal, or a signal that swings wildly when it should be steady.

Modern vehicles rely on a network of control modules that constantly compare sensor inputs against expected values. Each module continuously watches its assigned circuits, and if a reading strays beyond acceptable limits for longer than the programmed threshold, it logs P1671 and illuminates the Check Engine Light. What makes this code diagnostic-friendly is the freeze frame data that accompanies it. Think of freeze frame as a snapshot — it records engine speed, load, temperature, and vehicle speed at the precise instant the fault occurred. That snapshot becomes your roadmap for recreating the failure condition during testing.

P1671 typically surfaces alongside other codes rather than appearing alone. It signals an electrical problem in a subsystem — not necessarily a failed component, but often a wiring issue, a bad connection, or a blown fuse disrupting the circuit. Identifying which specific circuit triggered the code requires pulling related codes and using the freeze frame data as a guide.

Symptoms of P1671

The Check Engine Light remains illuminated after the fault is detected
The affected component operates inconsistently or stops working entirely
Fuel economy may climb noticeably in some vehicles
Performance degradation occurs if the faulty circuit controls a critical system
Limp-home mode activates on certain makes, restricting power to protect components
Unusual behavior from auxiliary systems — cooling fans, emissions controls, or similar — depending on which circuit is affected

What triggers P1671?

A blown fuse protecting the affected circuit — the most straightforward and cheapest cause
An internal driver fault within the control module itself, where the module can no longer properly toggle the circuit
Wiring that has opened, shorted, or chafed through from age, heat, or physical damage
Connectors compromised by corrosion, looseness, or bent pins preventing solid electrical contact
A deteriorated ground connection starving the circuit of proper reference voltage

Diagnosing P1671

Systematic diagnosis prevents unnecessary part replacements. Follow these steps:

Connect your OBD2 scanner, retrieve all stored codes, and capture the freeze frame data associated with P1671. Note the driving conditions recorded — you'll use these to trigger the fault again during testing.
Cross-reference any additional codes stored alongside P1671. Secondary codes often point directly to the failing component. Also search for TSBs (Technical Service Bulletins) for your specific make, model, and year — manufacturers frequently publish software updates or known fixes for P0xxx code patterns.
Perform a thorough visual inspection of the wiring harness and connectors tied to the affected circuit. Look for cracked insulation, melted wiring, green corrosion buildup, or connectors that are not fully seated.
Use a multimeter to check reference voltage, ground integrity, and signal continuity at the component itself. Compare your readings against manufacturer specifications.
Conduct a wiggle test on the harness while monitoring live data. Any signal dropouts or interruptions indicate a broken wire or intermittent connector failure.
Clear all codes, drive the vehicle through a complete drive cycle — including the specific conditions from your freeze frame — and verify that P1671 does not reappear.

Repair options and costs

Not every P1671 repair requires expensive parts. Work from simple to complex:

Wiring harness repair or connector replacement: $80–$250
Replacement of the faulty sensor or actuator: $150–$500
Control module repair or replacement: $300–$1,000

Labor rates vary by region, and some repairs may involve disassembly time that affects the final invoice.

The total investment to resolve P1671 typically falls between $80 and $1,000, depending entirely on which component fails. A methodical diagnosis that rules out wiring issues and connectors before purchasing a new control module or expensive sensor is the smartest approach. Most shops charge one hour of labor for electrical diagnosis, which is a worthwhile expense before committing to major repairs.

Can you drive with P1671?

Most vehicles remain drivable after P1671 sets. You may notice reduced performance, a disabled辅助 function, or slightly worse fuel economy, but the car should continue operating. However, if the fault causes stalling, prevents starting, or triggers warnings related to braking or steering systems, stop driving immediately and address it as a safety concern.