Code
P1663
LINCOLN
P — Powertrain
Fuel Demand Command Signal Circuit Malfunction
Views:
UK: 10
EN: 49
RU: 17
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the fuel demand command circuit
- Corroded, loose, or damaged connector(s) at PCM, fuel pump control module or fuel pump module
- Faulty fuel pump control module (FPCM) or fuel pump assembly
- Weak or missing power/ground to the control module or PCM
- Blown fuse or faulty relay in the fuel pump/control circuit
- Intermittent wiring fault caused by chafing, pinched harness or water intrusion
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- No-start or hard-start condition (engine cranks but fuel delivery reduced)
- Intermittent stalling or loss of power under load
- Poor acceleration or reduced engine performance
- Lower than normal fuel pressure or erratic fuel pressure readings
What to check
- Read and record freeze frame and full DTC list with a capable scan tool
- Check battery voltage and ground integrity (battery >= 12.4 V recommended during testing)
- Visually inspect fuses and fuel pump / fuel module relays related to fuel system
- Visually inspect harness and connectors at the PCM, fuel pump control module and fuel tank for corrosion, loose pins, water intrusion, or damage
- Backprobe the fuel demand command circuit and related power/ground while commanding fuel demand with a scan tool
- Wiggle the harness and connectors while monitoring signal for intermittent faults
Signal parameters
- Type: typically a PCM output to the fuel pump control module — often PWM or switched output (refer to vehicle-specific service data)
- Voltage range: 0–5 V logic expected on many systems; command high ~near battery voltage if switched power output (confirm in service manual)
- Duty cycle: 0–100% control used to command fuel demand (idle = low duty, high demand = higher duty)
- Behavior: signal should change when commanding fuel demand via scan tool; should be stable with engine running or when commanded by PCM
- Expected continuity: low resistance between PCM pin and control module pin (vehicle-specific pinouts required)
Diagnostic algorithm
- Retrieve and record DTC(s) and freeze frame data. Note conditions when DTC set (key on, engine running, load).
- Verify battery voltage and test grounds. Poor supply can cause spurious faults.
- Inspect fuses and relays for the fuel pump and fuel control circuits; replace if faulty.
- Visually inspect connector(s) and wiring between PCM, fuel pump control module (FPCM) and fuel pump for damage or corrosion. Repair any damaged wiring/connectors.
- With a scan tool, command fuel demand (or fuel pump on) and observe the command signal at the control module using a multimeter or oscilloscope. Verify voltage/duty cycle changes as commanded.
- Perform continuity and resistance checks between PCM pin and control module pin with connectors disconnected. Repair any opens/shorts.
- Wiggle test wiring and connectors while monitoring the signal to detect intermittent connectors or harness faults.
- If wiring and connectors are good but signal is incorrect or absent, bench-test or substitute the fuel pump control module (if available) and retest.
- If substituted FPCM does not correct and wiring/grounds are verified, consider PCM driver fault — verify with manufacturer procedure before replacing PCM.
- Clear codes and retest under the same conditions to confirm repair.
Likely causes
- Damaged or corroded connector at the fuel pump control module
- Open/short in the fuel demand command wiring (backprobe and wiggle test often reproduce)
- Faulty fuel pump control module or pump assembly
Fault status
Status
Fuel Demand Command Signal Circuit Malfunction — the powertrain control module detected an invalid, out-of-range, missing, or intermittent signal on the fuel demand command circuit.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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