P0117 — Engine Coolant Temperature Circuit Low Input — 5.9 Cummins 24-Valve (VP44)
Diagnostic reference for 5.9L Cummins 24-Valve (VP44) 1998.5–2002. Focus on diagnosing the ECT circuit low-input condition without step-by-step repair of…
What it means
The ECM detects an abnormally low voltage/resistance from the engine coolant temperature sensor circuit, indicating the sensor signal is below the expected range. On the 5.9L Cummins 24-Valve (VP44) this applies to Dodge Ram 2500/3500 1998.5–2002.1
Most likely causes
- ECT sensor internal short or failed sensor pulling signal low — Sensor element or connector fault causing low voltage reading to ECM.1
- ECT wiring short to ground or chafed harness in engine bay — Wiring between sensor and ECM shorted to ground, producing low input.1
- Corroded or loose ECT connector / poor terminal contact — High resistance or intermittent connection at sensor plug biases voltage low.1
- ECM reference voltage or pull-up circuit fault — ECM internal reference issue causing low circuit voltage reading.1
How to diagnose
- Verify code and freeze frame; confirm P0117 is present and note engine temp at set.
- Inspect ECT sensor connector for corrosion, oil intrusion, loose terminals; check harness for chafing near thermostat housing and along valve cover.
- Measure ECT sensor signal voltage at ECM harness with key on engine off; compare to expected range and to sensor disconnected condition.
- Check ECT sensor resistance/voltage at sensor connector versus temperature chart; look for out-of-range low reading.
- Inspect ECM connector and related grounds for corrosion/moisture; verify reference voltage supply to sensor circuit.
- If circuit tests normal, evaluate ECM input processing for the ECT circuit.
- Document findings before clearing code and retest after repair.
- Note: Do not perform step-by-step repair of safety-critical systems. Focus on diagnosis only.
Parts and tools you may need
- Digital multimeter
- Scan tool with live data
- Wiring diagram for 1998.5–2002 Cummins 24V
- Contact cleaner
- Inspection light
Tools you’ll need
- digital multimeter — Measures ECT signal voltage at the ECM harness and sensor resistance versus temperature to confirm a low-voltage/short condition for P0117.
- OBD-II scan tool — Reads P0117, freeze frame data, and live ECT PID to verify the fault and monitor sensor behavior during KOEO and running tests.
- wiring test light — Quickly checks for shorts to ground and verifies reference voltage presence on the ECT circuit without loading the ECM pull-up.
- terminal release tool set — Allows safe inspection and reseating of the ECT and ECM connectors to address corrosion or loose terminals causing low signal.
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 |
| 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 and sensor values are correct but code persists, have a qualified diesel technician evaluate the ECM input circuit. Do not attempt high-pressure fuel or brake system work. Seek professional diagnosis for intermittent electrical faults.
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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