DTC 312 — Engine Oil Temperature Signal Out of Range – High — International DT466E
DTC 312 on International DT466E (1996–2003) indicates the engine oil temperature sensor signal voltage is above its valid range. The ECM uses EOT for…
What it means
Engine oil temperature (EOT) sensor signal voltage is above its valid range. On this platform the code typically points to an open EOT sensor or circuit.1
Most likely causes
- Open EOT sensor element or internal sensor failure — An open sensor raises signal voltage out of range high. Typical on this platform for DTC 312.1
- Unplugged, corroded, or damaged EOT connector — Poor connection at the sensor raises signal voltage. Similar connector issues are noted for other temperature sensors on this platform.2
- Open or high-resistance in the EOT signal wire to ECM — A break or corrosion in the signal wire raises voltage seen by the ECM. Connector/wire faults are a common pattern for sensor out-of-range-high codes on this platform.2
- Signal wire shorted to voltage (reference/ power) — A short to a higher voltage source drives the signal above valid range. Short-to-voltage is a known cause for sensor out-of-range-high codes on this platform.3
How to diagnose
- Verify code with scan tool or flash codes; confirm DTC 312 is active and note freeze-frame conditions.
- Inspect EOT sensor connector for corrosion, moisture, or loose terminals; repair as needed.
- Check EOT sensor resistance/voltage at the sensor and at the ECM connector per service data; compare to known-good values.
- Inspect EOT signal wiring for chafing, opens, or shorts to voltage; repair wiring faults.
- Replace EOT sensor if electrical tests indicate an open element; clear code and retest.
- Confirm EOT reading is plausible with engine warm-up and that no related codes return.
Parts and tools you may need
- Digital multimeter
- Scan tool capable of Navistar three-digit codes
- Terminal cleaning supplies
- Replacement EOT sensor
Tools you’ll need
- OBD-II scan tool — Reads DTC 312 and freeze-frame data to confirm the high-voltage EOT fault and monitor live EOT readings during warm-up.
- Digital multimeter — Measures EOT sensor resistance and signal voltage at the sensor and ECM connector to detect an open element or wiring fault.
- Terminal test light — Checks for shorts to voltage on the EOT signal wire and verifies proper ECM reference/ground presence without loading the circuit.
- Inspection mirror — Allows visual inspection of the EOT sensor connector and wiring in the tight DT466E engine bay for corrosion, moisture, or chafing.
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 |
Typical US independent-shop figures; labor runs about $140–$200 per hour (dealers charge more). Confirm the diagnosis before buying parts.
When to see a pro
If wiring faults are extensive, if the code returns after sensor replacement, or if engine protection/derate symptoms appear, have a qualified diesel technician diagnose the harness and ECM inputs.
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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