DTC 155 — Intake Air Temperature Signal Out of Range – High — International DT466E

Diagnostic reference for International DT466E (1996–2003) Navistar three-digit code 155.

Updated October 15, 2026

What it means

Intake air temperature (IAT) signal voltage is above its valid range. On the DT466E this is Navistar code 155 for the intake air temperature sensor circuit. Typical on this platform: usually an open IAT sensor or circuit.¹

Most likely causes

1. Open IAT sensor or open signal wire causing high voltage reading — The IAT sensor circuit is open, which drives the signal voltage high and sets the code.¹
2. Corroded or unplugged IAT connector increasing resistance in the signal path — Connector corrosion or a loose/unplugged IAT connector can raise signal voltage. Similar sensor faults on this platform are often due to an unplugged/corroded connector or an open signal wire.²
3. Signal wire shorted to a higher voltage source — A short to voltage on the IAT signal wire pulls the voltage above the valid range. A comparable high-voltage sensor fault on this platform is a signal wire shorted to the 5 V reference.³

How to diagnose

1. Verify the code is present with a scan tool or flash codes and record freeze-frame conditions. Navistar three-digit DTCs are read by counting flashes of the amber engine lamp or with a scan tool.
2. Inspect the IAT sensor connector for corrosion, moisture, or being unplugged; compare to typical platform faults where an unplugged/corroded connector causes high-voltage sensor codes.
3. Check the IAT wiring harness for chafing, pinching, or exposure to heat that could create an open or a short to voltage; similar high-voltage sensor faults on this platform involve a signal wire shorted to the 5 V reference.
4. With key on, engine off, use a scan tool to view live IAT data and compare to ambient temperature; an implausibly high reading supports an open or shorted-high condition. Generic definition for this code is IAT signal voltage above its valid range.
5. Inspect related engine sensors and grounds in the intake area; platform sensor faults commonly involve open sensor or circuit issues.

Parts and tools you may need

• Digital multimeter
• Scan tool capable of Navistar three-digit codes
• Contact cleaner and dielectric grease
• Basic hand tools for connector access

Tools you’ll need

• OBD-II scan tool — Reads Navistar DTC 155 and live IAT data to confirm high voltage reading and compare to ambient temperature.
• Digital multimeter — Measures IAT sensor resistance and checks for open circuit or signal wire short to higher voltage with key on, engine off.
• Terminal release tool set — Allows safe inspection and reseating of the IAT connector pins to address corrosion or unplugged conditions causing high voltage.
• Inspection mirror and LED flashlight — Provides clear view of the IAT sensor and wiring harness in the intake area for chafing, heat damage, or moisture without disassembly.

Rough cost and difficulty

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 the wiring inspection shows damaged harness, intermittent faults persist after connector service, or the code returns with normal sensor readings, have a qualified diesel technician diagnose the ECM inputs and wiring integrity. Do not perform step-by-step repair of safety-critical systems. On the DT466E, HEUI injection uses high-pressure oil; avoid servicing high-pressure oil components without proper training.

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