FC 4572 — Aftertreatment DEF Tank Temperature – Abnormal Update Rate (SPN 3031 FMI 9) — Cummins ISX15

The ECM is not receiving DEF tank temperature updates at the expected rate on a Cummins ISX15 (2010–2017).

Updated October 15, 2026

What it means

The DEF tank temperature signal is not updating at the expected rate.¹

Most likely causes

1. DEF tank temperature sender (level/temperature/quality sender) internal fault or intermittent connection. — The sender assembly provides temperature data to the ECM; an internal fault or poor contact can cause an abnormal update rate.¹²
2. Wiring or connector corrosion / loose pins at the DEF tank sender or chassis harness. — Moisture, road salt or vibration can degrade the DEF tank harness connectors, leading to intermittent signal loss.¹²
3. Datalink / CAN communication issue affecting the DEF tank module signal. — A broader network fault can delay or drop messages from the DEF tank sender, producing an abnormal update rate.¹²
4. DEF tank heater circuit fault causing erratic temperature behavior. — A heater-related fault can produce temperature swings that the ECM interprets as abnormal updates.³

How to diagnose

1. Verify the fault is active and note freeze-frame conditions (ambient temperature, DEF level, recent refills).
2. Inspect DEF tank sender connector and chassis harness for corrosion, moisture, bent pins, and secure seating; repair as needed.
3. Check wiring continuity and isolation between the DEF tank sender and ECM per Cummins wiring diagrams; look for chafing near the tank and frame.
4. Use Insite to view live DEF tank temperature data; confirm the signal is updating at the expected rate and compare to ambient/engine conditions.
5. If the signal is intermittent, perform a wiggle test on the harness and connectors while monitoring live data.
6. Inspect the DEF tank sender assembly for contamination or damage; replace the sender if internal fault is suspected.
7. Clear codes and road test to confirm the fault does not return; monitor for companion DEF system codes.
8. If the issue persists, check CAN network integrity and related modules for communication faults.
9. Document findings and repairs; retest after repair.

Specs and test values

Parts and tools you may need

• Digital multimeter
• Insulation resistance tester
• Cummins Insite diagnostic software
• Wiring diagram for ISX15 CM2250/CM2350
• Dielectric grease
• Replacement DEF tank sender/level-temperature-quality assembly
• Basic hand tools and trim removal tools

Tools you’ll need

• diagnostic scan tool with Cummins Insite capability — Reads live DEF tank temperature data and freeze-frame to confirm signal update rate and active fault conditions.
• digital multimeter — Checks continuity and isolation of sender wiring and verifies power/ground at the DEF tank sender connector.
• inspection mirror and LED flashlight — Allows visual inspection of the DEF tank sender connector and harness for corrosion, moisture, and chafing in tight under-vehicle areas.
• terminal release tool set — Safely releases and reseats pins in the DEF tank sender and chassis harness connectors to correct loose or bent contacts.

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 fault returns after harness and sender checks, or if CAN/network faults are present, have a certified Cummins technician diagnose with Insite and OEM schematics. Do not attempt high-pressure fuel or aftertreatment service without proper training and safety equipment.

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