P1663 — FDCS Circuit Failure — 7.3 Power Stroke

P1663 is a Ford-enhanced code for the 7.3L Power Stroke (1999–2003 Super Duty/Excursion). It indicates a fault in the fuel delivery command signal (FDCS)…

Updated October 15, 2026

What it means

Generic definition: Ford enhanced code: fault in the fuel delivery command signal (FDCS) circuit from the PCM to the injector driver module. On the 7.3L the FDCS tells the IDM how much fuel to deliver.¹

Most likely causes

1. Open or short in the PCM-to-IDM FDCS wiring/harness — Chafed, corroded, or oil-soaked wiring between the PCM and the IDM can interrupt the FDCS signal. Inspect the harness routing, connectors, and pins for damage, moisture, or poor contact.¹
2. IDM power or ground fault — Loss of battery power or ground to the IDM will prevent proper FDCS reception and IDM operation. Verify IDM power/ground integrity and connections at the driver-side fender module.¹²
3. Faulty injector driver module (IDM) — An internal IDM failure can cause the FDCS circuit to be reported as faulty and often sets P1660/P1662 alongside P1663.¹²
4. PCM driver or internal fault for FDCS — The PCM output driver for the FDCS line may be failed or the PCM may have a power/ground issue affecting communication to the IDM.¹²
5. Corroded or loose IDM/PCM connectors — Connector pin fretting, corrosion, or loose retention at the IDM or PCM can create intermittent FDCS faults, commonly logged with P1660/P1662.¹³²

How to diagnose

1. Verify the code and freeze-frame data; confirm P1663 is present and note any accompanying P1660/P1662.
2. Visually inspect the IDM and PCM connectors and the PCM-to-IDM harness for chafing, oil contamination, corrosion, or loose pins.
3. Check IDM power and ground circuits for correct voltage and low resistance to battery/chassis ground.
4. Perform a pin-to-pin continuity and isolation check of the FDCS wire between the PCM and IDM connector; look for opens, shorts to ground or power.
5. Inspect IDM connector terminals for spread pins, corrosion, or moisture; clean and reseat as needed.
6. If wiring and power/ground test good, monitor IDM enable and FDCS signal behavior with a scan tool while cranking to see if the PCM is commanding the IDM.
7. Swap or bench-test the IDM if available; a known-good IDM can isolate an internal module fault.
8. If the IDM tests good and wiring is intact, evaluate PCM power/ground and consider PCM internal driver fault as the remaining cause.

Specs and test values

Parts and tools you may need

• Digital multimeter
• Scan tool with Ford enhanced codes
• Wiring diagram for 7.3L Power Stroke PCM-to-IDM circuits
• Contact cleaner and dielectric grease
• Basic hand tools for connector access

Tools you’ll need

• digital multimeter — Checks IDM power/ground voltage and FDCS wire continuity/isolation between PCM and IDM.
• OBD-II scan tool — Reads P1663 and related codes and monitors IDM enable/FDCS command while cranking.
• wiring test light or logic probe — Quickly verifies FDCS signal presence from PCM to IDM during cranking without loading the circuit.
• terminal release tool set — Allows safe inspection, cleaning, and reseating of IDM/PCM connector pins for corrosion or spread terminals.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If the truck is crank-no-start, or if diagnosis points to PCM internal driver failure, have a qualified diesel technician confirm with module testing before replacing the PCM. High-pressure oil and injector circuits are safety-critical; do not attempt internal IDM or PCM repairs without proper equipment.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources