P1660 — Output Circuit Check Signal High — 7.3 Power Stroke
P1660 is a Ford-enhanced code: the IDM output circuit check (OCC) signal to the PCM is reading high on the 1999–2003 7.3L Power Stroke.
What it means
P1660 is a Ford enhanced code: the output circuit check (OCC) signal between the injector driver module (IDM) and the PCM is reading high. On the 7.3L Power Stroke the IDM is the module that drives the HEUI injectors. The engine uses HEUI injection with a high-pressure oil pump; there is no common rail or high-pressure fuel pump.12
Most likely causes
- IDM power/ground or internal IDM failure — The IDM is mounted on the driver-side fender and powers the eight HEUI injectors. Loss of power, ground, or internal failure can set P1660. Typical on this platform: 7.3L Power Stroke — HEUI, IDM/output-circuit faults P1660, P1662, P1663.1
- Chafed or corroded IDM wiring/harness — Wiring between the PCM and IDM, or the IDM connectors, can be damaged by heat/vibration.1
- Under-Valve-Cover Harness (UVCH) degradation affecting injector circuits — Oil-soaked, chafed UVCHs are a known failure point and can cause injector and glow-plug circuit codes. While P1660 is an IDM/output fault, degraded UVCHs contribute to injector circuit issues on this platform.1
- PCM power/ground or internal PCM fault — PCM internal KAM/ROM errors are common on this platform and often relate to PCM power/ground issues. P0603/P0605 are typical PCM internal faults.1
How to diagnose
- Verify code and freeze-frame; confirm P1660 is present and note accompanying codes such as P1662/P1663 or injector circuit codes.
- Inspect IDM power and ground circuits and connectors for corrosion, loose pins, or heat damage; check IDM fuse/relay per wiring diagram.
- Perform a visual and wiggle test of the PCM-to-IDM harness for chafing, oil contamination, or damaged insulation.
- Check IDM connector pin tension and clean as needed; measure IDM supply voltage with key on.
- Inspect both Under-Valve-Cover Harnesses for oil saturation, chafing, and connector integrity; look for signs of injector circuit faults.
- Review recent repairs or moisture exposure that could affect PCM/IDM grounds.
- If no wiring faults are found, consider IDM functionality and PCM communication integrity; compare with known-good values.
- Clear codes, test drive, and re-scan to confirm P1660 returns.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| Battery and charging voltage | 12.6–12.7 V at rest when fully charged; about 13.5 V running | Engine off, then running with loads on | DieselHub |
Parts and tools you may need
- Digital multimeter
- Scan tool capable of Ford enhanced codes
- Wiring diagram for 1999–2003 7.3L Power Stroke
- Contact cleaner and dielectric grease
- Inspection light
Tools you’ll need
- digital multimeter — Measures IDM supply voltage, ground continuity, and pin-to-pin resistance to isolate power/ground or harness faults causing P1660.
- OBD-II scan tool — Reads and clears P1660 and related injector/IDM codes and freeze-frame data to confirm the fault and monitor recurrence after repairs.
- inspection mirror — Allows visual inspection of the IDM and PCM-to-IDM harness routing in tight engine-bay areas for chafing, oil contamination, or heat damage.
- terminal release tool set — Safely releases and reseats IDM and UVCH connector terminals to check pin tension and corrosion without damaging the connectors.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| Injector wiring harness / under-valve-cover harness | $50–$300 | 2–5 hrs | Shop |
| IDM (injector driver module), reman | $330–$600 | 1–2 hrs | DIY with tools and a manual |
| ECM/PCM replacement (programmed) | $600–$2,000 | 1–3 hrs | Shop |
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 IDM or PCM needs replacement or programming, or if high-pressure oil system work is required, have a qualified diesel technician perform the work. Do not attempt repairs to safety-critical high-pressure systems without proper training and tools.
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
Repair videos: P1660 on the 7.3 Power Stroke
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 7.3 Power Stroke? This goes straight to the editor — it is not published.