P0117 — Engine Coolant Temperature Circuit Low Input — 7.3 Power Stroke
Diagnostic reference for 7.3L Power Stroke (1999-2003 Super Duty/Excursion).
What it means
The PCM detects abnormally low voltage/resistance from the engine coolant temperature sensor circuit, indicating the ECT signal is below the expected range.1
Most likely causes
- ECT sensor internal short or failed thermistor — Sensor reads out of range low; typical failure mode for P0117 on this platform.1
- ECT sensor connector damaged, corroded, or oil/coolant contaminated — Poor terminal contact or contamination pulls signal low.1
- Wiring harness chafed/shorted to ground between ECT sensor and PCM — Short to ground forces low voltage on the signal wire.1
- PCM reference voltage or ground fault affecting ECT circuit — Abnormal supply/ground to the sensor circuit can cause low input reading.1
How to diagnose
- Verify code and freeze frame; confirm P0117 is present and not accompanied by other ECT-related codes.
- Inspect ECT sensor connector and wiring for corrosion, coolant intrusion, or chafing; repair wiring faults before replacing parts.
- Measure ECT sensor resistance/voltage at the sensor and at the PCM connector to isolate sensor vs harness fault.
- Check PCM reference voltage and ground circuits for the ECT input; confirm integrity of the signal return path.
- If sensor and wiring test normal, evaluate PCM input for internal fault.
- Clear codes, road test, and confirm monitor readiness.
Parts and tools you may need
- Digital multimeter
- Wiring diagram for 7.3L Power Stroke ECT circuit
- ECT sensor (OEM spec)
- Dielectric grease
- Terminal repair kit
Tools you’ll need
- digital multimeter — Measures ECT sensor resistance and reference voltage at the sensor and PCM connector to isolate sensor vs harness fault.
- OBD-II scan tool — Reads P0117, freeze frame, and live ECT data to confirm the low signal and monitor changes after repairs.
- wiring repair kit — Allows repair of chafed, corroded, or coolant-contaminated ECT wiring and connector terminals found during inspection.
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 |
| Temperature or pressure sensor (coolant, intake air, oil, fuel temp) | $30–$150 | 0.3–1.5 hrs | Easy DIY |
| Engine wiring harness section | $100–$500 | 2–5 hrs | Shop |
| 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 wiring tests normal but code returns, or if PCM input is suspect, have a qualified diesel technician perform PCM circuit testing and, if needed, PCM evaluation. Do not attempt high-pressure oil or safety-critical repairs 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
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