Damaged wiring, chafing or corrosion in the fuel demand signal circuit between the PCM and the fuel pump driver module; Poor connection or corroded terminals at the PCM, driver module or fuel pump connector; Faulty fuel pump driver or fuel pump control module; Low or unstable supply voltage or poor earth to the driver module or PCM; Water ingress or heat damage at the module, often mounted near the rear of the vehicle (location depends on model); Internal PCM driver fault or outdated PCM calibration.

P1663

Fuel Demand Command Signal Circuit Malfunction.

Mercury
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
6: AreaComputer and output circuits
63: FaultThe specific fault in that area

What it means

On Mercury (Ford group) vehicles, P1663 means the powertrain control module has detected a fault in the Fuel Demand Command Signal circuit. This is the signal used to tell the fuel pump driver or fuel pump control module how much fuel pressure or flow is wanted on vehicles with a returnless or variable-speed fuel system. The PCM set the code because the commanded signal and the circuit's expected electrical state did not agree, such as an open, short or out-of-range reading.

Symptoms

Malfunction indicator lamp on
Long cranking or hard starting
Engine cutting out or stalling, especially under load
Hesitation or loss of power when accelerating
Poor fuel economy or rough running
Fuel pump running at the wrong speed or noise from the pump

Possible causes

Damaged wiring, chafing or corrosion in the fuel demand signal circuit between the PCM and the fuel pump driver modulelikely
Poor connection or corroded terminals at the PCM, driver module or fuel pump connectorlikely
Faulty fuel pump driver or fuel pump control modulepossible
Low or unstable supply voltage or poor earth to the driver module or PCMpossible
Water ingress or heat damage at the module, often mounted near the rear of the vehicle (location depends on model)possible
Internal PCM driver fault or outdated PCM calibrationrare

How to diagnose

Read all stored and pending codes and note freeze frame data, then check for related fuel pressure, fuel pump or power supply codes.
Check for relevant technical service bulletins and calibration updates for the specific model and engine.
Visually inspect the wiring and connectors for the fuel pump driver module and fuel pump, looking for chafing, corrosion, water ingress and loose pins.
Check battery condition and charging voltage, and verify power and earth supplies to the driver module against the wiring diagram.
With a scan tool, compare the commanded fuel pump duty or fuel demand with actual fuel pressure, if the model supports this data.
Back-probe the demand signal circuit with a multimeter or oscilloscope to confirm the signal is present, clean and follows the PCM command; check for opens, shorts to earth or shorts to voltage.
Measure actual fuel pressure with a gauge and compare with the manufacturer's specification for the model.
If wiring, supplies and earths are good, test or substitute the driver module as per the manufacturer's procedure before suspecting the PCM.

How to fix

Repair or replace damaged wiring and clean or replace corroded terminals and connectors in the demand signal circuit.
Restore good power and earth connections to the driver module and PCM.
Replace the fuel pump driver or control module if it is confirmed faulty.
Fit a replacement fuel pump if it is drawing excessive current or is shown to be at fault.
Apply an updated PCM calibration only if the manufacturer lists it as a fix for this fault, and replace the PCM only after all else is ruled out.

Can I keep driving?

Medium severity

The car may run, but the fuel supply can become unreliable and cause stalling or a no-start. Limit driving and get it checked soon, avoiding situations where a sudden loss of power would be dangerous.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.