Diesel Trouble Codes

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…

Updated September 2, 2026

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

  1. ECT sensor internal short or failed sensor pulling signal low — Sensor element or connector fault causing low voltage reading to ECM.1
  2. ECT wiring short to ground or chafed harness in engine bay — Wiring between sensor and ECM shorted to ground, producing low input.1
  3. Corroded or loose ECT connector / poor terminal contact — High resistance or intermittent connection at sensor plug biases voltage low.1
  4. ECM reference voltage or pull-up circuit fault — ECM internal reference issue causing low circuit voltage reading.1

How to diagnose

  1. Verify code and freeze frame; confirm P0117 is present and note engine temp at set.
  2. Inspect ECT sensor connector for corrosion, oil intrusion, loose terminals; check harness for chafing near thermostat housing and along valve cover.
  3. Measure ECT sensor signal voltage at ECM harness with key on engine off; compare to expected range and to sensor disconnected condition.
  4. Check ECT sensor resistance/voltage at sensor connector versus temperature chart; look for out-of-range low reading.
  5. Inspect ECM connector and related grounds for corrosion/moisture; verify reference voltage supply to sensor circuit.
  6. If circuit tests normal, evaluate ECM input processing for the ECT circuit.
  7. Document findings before clearing code and retest after repair.
  8. Note: Do not perform step-by-step repair of safety-critical systems. Focus on diagnosis only.

Parts and tools you may need

Rough cost and difficulty

Parts cost varies by source; labor varies by shop. Diagnostic time is typically 0.5–1.5 h. Actual repair cost depends on whether fault is sensor, wiring, or ECM.

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.

Sources

  1. Curated DTC seed — 5.9 Cummins 24-Valve (VP44) (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎