P1665 — Injection Pump Control Module Communication Loss

P1665 — Injection Pump Control Module Communication Loss. Loss of communication with the injection pump control module can cause poor engine operation, unexpected stalling, or failure to restart.

For Ford vehicles

injection pump control module comunications

vehicle

Is it safe to drive?

Do not drive with active P1665 Loss of communication with the injection pump control module can cause poor engine operation, unexpected stalling, or failure to restart. Stop driving until the fault is repaired and P1665 no longer returns.

Typical symptoms

The check-engine light may illuminate with P1665 stored in the controller
The engine may crank but fail to start when injection pump control module communication is lost
The engine may stall unexpectedly or fail to restart after being shut off
Engine operation may become rough, hesitant, or unusually noisy
Engine power may decrease or enter a fail-safe operating mode
A fuel-pressure or pump-related warning may appear on supported vehicles

Common causes

An open, short, or damaged wire in the injection pump control module communication circuit
A loose, corroded, or water-contaminated connector between the injection pump control module and the vehicle controller
Insufficient battery voltage or a poor power or ground connection at the injection pump control module
A defective injection pump control module that no longer communicates with the powertrain controller
A communication-circuit or controller fault on the powertrain control module side of the link
A CAN network, termination, or wiring fault where the injection pump control module uses a vehicle network

How to diagnose with an OBD scanner

Capture P1665 with an OBD2 scanner Connect an OBD2 scanner such as ELM327 with AIScanAuto or a similar tool. Read stored and current DTCs, freeze-frame data, and any available communication-status information. Record whether P1665 appears during cranking, startup, idle, or stalling before clearing it.
Inspect the module wiring and connectors With the battery disconnected using the vehicle service procedure, inspect the harness between the injection pump control module and the powertrain controller. Look for chafing, broken conductors, corrosion, water intrusion, bent terminals, and improperly seated connectors.
Verify module power and grounds Check the injection pump control module supply, ground, and wake circuits with a multimeter. Compare the readings with the manufacturer wiring diagram and service specifications. Repair excessive voltage drop, poor grounds, or damaged power feeds before condemning the module.
Test the communication circuit Use the service wiring diagram to determine whether the link is a dedicated circuit or a network connection. Confirm that command and response signals reach the injection pump control module where applicable. A missing response can indicate wiring, controller, or module failure.
Isolate the suspected module After power, ground, and wiring have been verified, isolate the injection pump control module using approved diagnostic procedures. If communication remains absent and the controller side is confirmed good, the module becomes a likely cause of P1665.
Repair and confirm the P1665 repair Repair the damaged wiring or connector, replace a confirmed faulty module, or address the powertrain controller fault as testing indicates. Program or calibrate a replacement module when required, then clear P1665 and verify communication, starting, idle operation, and fuel delivery.

Approximate repair cost

A rough independent-shop estimate is $300-$2,000 USD for troubleshooting and repair, depending on whether the fault is wiring, a connector, or the injection pump control module itself. These figures are estimates only, not verified quotes, and vary by region, vehicle, and labor rates.

Common questions

What does P1665 specifically identify?

P1665 identifies a communication failure between the vehicle controller and the injection pump control module, preventing normal confirmation or control of fuel-delivery functions.

Can the vehicle be driven with P1665?

An active P1665 should not be ignored because loss of module communication may cause stalling, poor power, or failure to restart, especially during normal traffic.

Does P1665 prove the injection pump control module is defective?

No. P1665 can also result from damaged wiring, a bad connector, inadequate power or ground, a network fault, or a failure on the controller side of the communication link.

What should be checked before replacing the module?

First capture the code with an OBD2 scanner, then inspect the harness and connectors and verify module power and ground. Module replacement should follow those checks when the communication fault remains.

P1665 — ---

The engine control module logs trouble code P1665 when it spots an electrical problem somewhere in the sensor and actuator network. Put simply, the module is telling you that one or more circuits responsible for reading conditions or commanding action are not behaving as expected. P1665 falls into the generic OBD2 code family, which means any make or model equipped with the standardized on-board diagnostics system can store this code.

The control module does not trigger the warning light after a single bad reading. It watches the problem repeat across multiple drive cycles and under specific temperature, load, and speed conditions before it considers the fault confirmed. When P1665 is set, the freeze frame data recorded at the same time becomes your roadmap — it pinpoints the exact engine load, rpm, coolant temperature, and vehicle speed present when the failure occurred. Recreating those conditions on a test drive lets you observe the fault firsthand.

Symptoms of P1665 typically include a steady or flashing Check Engine Light, reduced fuel economy in some vehicles, and either intermittent operation or complete failure of whatever system the faulty circuit controls. Depending on which component is affected, the car may drop into limp-home mode, which limits speed and power to protect the drivetrain until the problem is addressed.

Symptoms

Check Engine Light illuminated on the dashboard
Noticeable increase in fuel consumption
The affected sensor or actuator works only intermittently, or stops working entirely
Vehicle may enter limp mode, restricting acceleration and top speed
In rare cases, related systems such as traction control or emission controls become unavailable
Stored freeze frame data points to abnormal readings at the moment of failure

Causes

The most frequent culprit behind P1665 is a weak or failed driver circuit inside the engine control module itself. When the module cannot properly switch a circuit on or off, it interprets the result as a fault. Beyond the module, degraded ground connections rank high on the list — a loose or corroded ground prevents circuits from functioning correctly under load. Damaged connectors with bent pins, moisture intrusion, or corrosion also generate this code regularly. A blown fuse that feeds the affected circuit will obviously shut down operation and trigger the fault. Finally, wiring insulation that has chafed through or been chewed by rodents creates open circuits or short-to-ground conditions that the module flags as P1665.

How to Diagnose

Pinpointing the root cause of P1665 requires a systematic approach rather than guesswork:

Connect an OBD2 scanner, retrieve code P1665, and record all freeze frame data before clearing anything — this snapshot tells you exactly what was happening in the engine when the fault appeared.
Look for any related trouble codes stored alongside P1665. Codes in the same system often point to the real problem faster than chasing the symptom code alone. Check manufacturer TSB databases for known fixes or software updates that apply to your vehicle.
Perform a hands-on inspection of the wiring harness and connectors associated with the suspect circuit. Pull back protective looms, look for broken insulation, corroded terminals, and any signs of overheating or melted plastic.
With a multimeter, verify that reference voltage, ground integrity, and signal wires all read correctly at the component connector. Compare your findings against factory specifications.
Conduct a wiggle test on the harness while monitoring live data — any signal dropout or irregular reading while physically stressing the wiring confirms an intermittent break.
Clear the code, drive the vehicle through the conditions captured in the freeze frame, and recheck for P1665. If it returns, you have confirmed the fault and can proceed to repair with confidence.

Repair Options

Repair costs for P1665 vary widely depending on which part actually failed:

Wiring harness repair or connector replacement: $80–$250
Faulty sensor or actuator replacement: $150–$500
Engine control module diagnosis or repair: $300–$1,000

The total cost to fix P1665 typically falls between $80 and $1,000. Always start with visual inspection and electrical testing before committing to expensive part replacements. In the majority of cases, cleaning a corroded connector, splicing a broken wire, or replacing a blown fuse resolves the issue for under $250.

Can You Drive with P1665?

Most vehicles remain drivable when P1665 is stored, though you may notice sluggish acceleration, higher fuel usage, or a disabled auxiliary system depending on which circuit is affected. If the car exhibits stalling, hard-starting, or warnings related to braking and steering assist, treat the situation as urgent and have the vehicle towed to a repair facility immediately.