DTC 331 — Injection Control Pressure Above System Working Range — International DT466E

DTC 331 on International DT466E (1996–2003) indicates the ECM has seen injection control pressure above the normal working range. The code is a Navistar…

Updated October 15, 2026

What it means

Injection control pressure is above its normal working range. On the DT466E this is a HEUI system fault monitored via the ICP sensor and controlled by the IPR valve; the ECM uses engine oil pressure to actuate unit injectors.¹

Most likely causes

1. IPR valve sticking or failing to relieve pressure — The injection pressure regulator can stick closed or respond slowly, allowing ICP to climb above the ECM’s target. Typical on this platform for DTC 331.¹
2. ICP sensor reading high / sensor drift — A biased or failing ICP sensor can report pressure higher than actual, setting an over-range condition.¹
3. ICP sensor signal circuit fault (short to voltage or wiring issue) — An electrical fault on the ICP signal circuit can drive the sensor voltage above its valid range, mimicking high pressure. Related ICP signal out-of-range behavior is documented for this platform.²
4. High-pressure oil system restriction preventing pressure bleed-off — A restriction in the high-pressure oil return or a stuck component can keep ICP elevated. High-pressure oil control issues are characteristic of HEUI faults on this engine.³

How to diagnose

1. Verify the code with a Navistar-compatible scan tool and confirm active vs. historical status; note engine conditions when set.
2. Inspect ICP sensor connector and wiring for oil intrusion, corrosion, chafing, or shorts to voltage; check sensor supply and ground circuits.
3. Monitor live ICP voltage and pressure with a scan tool during key-on/engine-off, cranking, and idle; compare to expected values and look for implausible high readings at rest.
4. Command IPR duty cycle with a scan tool and observe ICP response; a sluggish or non-responsive change suggests a sticking IPR or control circuit issue.
5. Check engine oil level, condition, and for aeration; verify correct oil viscosity and that the high-pressure oil pump inlet is unobstructed. High-pressure oil problems affect ICP control on this HEUI system.
6. Inspect high-pressure oil rails, fittings, and injector O-rings for leaks or restrictions that could alter pressure regulation; note that low ICP faults are common with leaks, while over-range can indicate a bleed-off restriction.
7. If the ICP sensor reads pressure with engine off, evaluate sensor and circuit integrity; this pattern is associated with ICP sensor faults on the DT466E.
8. Review related codes (e.g., IPR circuit/self-test, ICP signal out of range) to isolate electrical vs. mechanical causes.

Parts and tools you may need

• Navistar-compatible scan tool capable of reading three-digit flash codes and live ICP/IPR data
• Digital multimeter
• Lab scope or graphing multimeter for sensor waveform
• Basic hand tools for sensor and IPR inspection
• Clean engine oil and correct specification filter

Tools you’ll need

• Navistar-compatible scan tool — Reads and clears DTC 331 and monitors live ICP pressure/voltage and IPR duty cycle to confirm active vs historical status and test control response.
• Digital multimeter — Checks ICP sensor supply, ground, and signal circuits for shorts to voltage, wiring faults, and implausible sensor readings with engine off.
• High-pressure oil system pressure test kit — Verifies actual high-pressure oil pressure against scan data to identify IPR sticking or bleed-off restrictions causing over-range ICP.
• Borescope — Inspects high-pressure oil rails, fittings, and injector O-rings for restrictions or leaks that can affect ICP regulation without full 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 ICP remains high under commanded control, if the engine exhibits hard start, rough running, or unexpected derate, or if high-pressure oil service is required, have a qualified diesel technician perform pressure testing and component evaluation. Do not service high-pressure oil components without proper training and safety precautions.

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