P1677 — Alternative Fuel Module Communication Failure

P1677 — Alternative Fuel Module Communication Failure. P1677 can cause the powertrain controller to use a default fuel strategy, producing hesitation, misfires, or stalling.

For Ford vehicles

alternative fuel supply control module communication circuit

vehicle

Is it safe to drive?

Caution: diagnose P1677 promptly P1677 can cause the powertrain controller to use a default fuel strategy, producing hesitation, misfires, or stalling. Drive only if engine operation and fuel delivery remain normal and there is no fuel odor. Stop immediately if the engine runs roughly, stalls, or any fuel leak is suspected.

Typical symptoms

The check-engine light or malfunction indicator illuminates with P1677 stored.
A scan tool reports lost communication or an invalid signal from the alternative fuel supply control module.
Alternative-fuel sensor information is unavailable, implausible, or remains frozen.
The powertrain controller may use a default fuel strategy instead of the commanded alternative-fuel calibration.
Engine hesitation, rough idle, hard starting, misfires, or stalling may occur.
Fuel delivery may be restricted if the alternative-fuel injector, valve, or pressure-control function enters a fail-safe mode.

Common causes

Open or high-resistance power, ground, or communication wiring to the alternative fuel supply control module.
Corroded, loose, or bent connector terminals at the alternative fuel module or powertrain controller.
Failed internal communication circuitry within the alternative fuel supply control module.
A damaged module power supply, poor engine or chassis ground, or voltage drop under load.
Chafed harness wiring near moving or hot vehicle components.
Incorrect module installation, coding, or calibration after a control-module replacement.

How to diagnose with an OBD scanner

Confirm P1677 and capture data Connect an OBD scanner using ELM327 or AIScanAuto, then read stored and pending codes. Save the P1677 freeze-frame information, note any additional fuel-system codes, and check whether communication with the alternative fuel supply control module is reported as lost. Do not erase P1677 before collecting this information.
Inspect the module and wiring Locate the alternative fuel supply control module using the vehicle wiring diagram. Inspect its connector, harness routing, and nearby grounds for corrosion, heat damage, chafing, water intrusion, or terminals that are pushed back. Repair damaged wiring and reseat affected connectors before condemning the module.
Verify power and ground integrity Using the correct circuit specifications, test the module's supply and ground with a multimeter. Check for excessive voltage drop under load and confirm that the engine ground is clean and secure. Also test for short circuits to power or ground if the fuse or supply does not behave as specified.
Test the communication circuit Follow the manufacturer wiring diagram to identify the communication or reference circuit. Check continuity, shorts, and signal behavior with the appropriate meter or oscilloscope. If the vehicle uses a shared network, verify the module's bus connection and relevant termination; do not assume a connector pin is a network wire without the correct pinout.
Compare commanded and received data With the ignition commanded on and the engine running where safe, compare alternative-fuel sensor readings with the powertrain controller's commanded values. Where equipped, inspect fuel composition, pressure, temperature, injector-pulse, or valve-command data to determine whether P1677 reflects an open circuit, failed module, or missing controller command.
Repair and verification scan After repairing the wiring, connector, ground, or module, clear the stored codes with the scanner. Cycle the ignition as required, confirm that the alternative fuel module communicates and returns plausible live data, verify fuel-related adaptive values, and road-test for hesitation, misfire, or stalling.

Approximate repair cost

Rough independent-shop planning ranges are $100–$225 for electrical diagnosis and scan time, $180–$650 for connector, ground, or harness repair, and $500–$1,500 or more if the alternative fuel supply control module requires replacement and coding. These figures are estimates, not verified repair quotes, and costs vary by region, labor rate, vehicle design, and parts availability.

Common questions

What does P1677 specifically identify?

P1677 identifies a malfunction in the communication circuit used by the alternative fuel supply control module. The exact module, wires, and electrical test values depend on the vehicle's fuel-system design.

Is P1677 a serious fault?

P1677 can be serious if the powertrain controller loses alternative-fuel data and falls back to an incorrect fueling strategy. The vehicle may run roughly, hesitate, misfire, or stall even though the stored code concerns communication.

Can the vehicle be driven with P1677?

Limited driving may be possible if the engine runs normally, fuel delivery is stable, and there is no leak or fuel odor. Continued operation is not advisable if P1677 remains active or is accompanied by stalling, misfires, or abnormal fuel consumption.

Does P1677 always require module replacement?

No. A damaged connector, corroded ground, open wire, poor module supply, or incorrect installation can produce P1677. The module should be condemned only after its power, grounds, wiring, communication signals, and installation have been tested.

P1677 — ---

When your scan tool pulls code P1677, the vehicle's control module is reporting a fault in the sensor and actuator circuits. This code belongs to the manufacturer-specific portion of the OBD2 system, which means it covers components unique to certain vehicle platforms rather than a universal emissions-related issue. The control unit detects the problem by monitoring voltage, resistance, or signal patterns from the affected circuit and comparing them against factory specifications.

To trigger P1677, the module typically needs to see the abnormality persist across multiple drive cycles. Once it confirms the fault, it saves a freeze frame snapshot — capturing engine speed, load percentage, coolant temperature, and vehicle speed at the exact moment the problem occurred. Technicians use that snapshot to recreate driving conditions during testing, which dramatically speeds up the diagnosis.

The "---" designation in the code description refers to a specific circuit or component that varies by manufacturer. When the PCM detects signals outside acceptable ranges, it sets P1677 and illuminates the Check Engine Light. Whether symptoms appear immediately or develop over time depends on whether the fault is intermittent or permanent.

Symptoms of P1677

P1677 affects how your vehicle operates, though the severity varies case by case:

The related system may work intermittently or stop functioning altogether
The Check Engine Light stays illuminated on the dashboard
Fuel economy can worsen noticeably during city or highway driving
Some vehicles enter limp mode, limiting power and speed to protect drivetrain components
Acceleration may feel sluggish or unresponsive
Certain auxiliary systems — such as traction control or adaptive features — could disable
In rare cases, the engine may stall at idle or hesitate during throttle transitions

Common Causes Behind P1677

The root cause usually stems from one of these issues, listed from most to least frequent:

Corrosion, looseness, or physical damage at the electrical connector feeding the affected circuit
An open or shorted wire within the harness — often from age, heat damage, or accidental pinching
A poor ground connection at the component or control module
A blown fuse protecting that specific circuit
Failure of the sensor or actuator itself — the actual device has died or weakened
A fault within the control module's driver circuit, where the PCM cannot properly send or receive signals

Diagnosing P1677 Step by Step

Follow this structured approach to avoid misdiagnosis and unnecessary replacements:

Connect an OBD2 scanner, verify P1677 is stored, and record all freeze frame data before clearing anything — this tells you exactly what conditions triggered the fault.
Look for any related trouble codes. P-codes appearing alongside P1677 often point toward the primary problem, such as a shorted sensor causing multiple circuit faults.
Search the manufacturer's technical service bulletins using your VIN. Many P1677 occurrences have documented factory solutions, software calibrations, or known defects.
Perform a visual inspection of the wiring harness and connectors tied to the --- circuit. Look for cracked insulation, green corrosion buildup, bent pins, or wires pulled free from their terminals.
Use a multimeter to check reference voltage, ground integrity, and signal continuity at the component connector. Compare readings to factory specifications.
Conduct a wiggle test on the harness while monitoring live data — any signal dropouts indicate broken wires inside the insulation.
Clear P1677, drive through a complete cycle including the freeze frame conditions, and verify the code does not reappear.

Repair Options and What They Cost

Labor rates and part prices assume a typical independent repair shop in the United States:

Wiring harness repair or connector replacement: $80–$250
Sensor or actuator replacement: $150–$500
Control module diagnosis and repair: $300–$1,000

Always tackle the most likely culprits first. In over 80 percent of cases, P1677 stems from damaged connectors or broken wires — not from a failed control module or expensive actuator. Spending $50 on a new connector and 30 minutes of diagnostic time prevents wasting $800 on a part that wasn't actually faulty.

Can You Drive With P1677?

Most vehicles remain driveable when P1677 is active, though you may notice reduced performance, diminished fuel economy, or an inoperable auxiliary system. Treat the code as urgent if you experience stalling, failure to start, or warnings related to braking and steering assist. In those situations, have the vehicle towed to avoid further damage.