Diesel Trouble Codes

P0117 — Engine Coolant Temperature Circuit Low Input (7.3 Power Stroke)

Diagnostic reference for 7.3L Power Stroke (1999-2003 Super Duty/Excursion).

Updated September 2, 2026

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

  1. ECT sensor internal short or failed thermistor — Sensor reads out of range low; typical failure mode for P0117 on this platform.1
  2. ECT sensor connector damaged, corroded, or oil/coolant contaminated — Poor terminal contact or contamination pulls signal low.1
  3. Wiring harness chafed/shorted to ground between ECT sensor and PCM — Short to ground forces low voltage on the signal wire.1
  4. 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

  1. Verify code and freeze frame; confirm P0117 is present and not accompanied by other ECT-related codes.
  2. Inspect ECT sensor connector and wiring for corrosion, coolant intrusion, or chafing; repair wiring faults before replacing parts.
  3. Measure ECT sensor resistance/voltage at the sensor and at the PCM connector to isolate sensor vs harness fault.
  4. Check PCM reference voltage and ground circuits for the ECT input; confirm integrity of the signal return path.
  5. If sensor and wiring test normal, evaluate PCM input for internal fault.
  6. Clear codes, road test, and confirm monitor readiness.

Parts and tools you may need

Rough cost and difficulty

Parts cost varies by source and region; labor varies by shop. Estimates are indicative only.

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 fuel or safety-critical repairs without proper training and tools.

Sources

  1. Curated DTC seed — 7.3 Power Stroke (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎