Code Details
| Display code | SPN 1569 FMI 31 |
|---|---|
| SPN | 1569 |
| FMI | 31 |
| OEM code | None listed |
| Manufacturer | Isuzu |
| System | Engine protection / aftertreatment |
| Component | ECM engine protection strategy |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-11 |
Plain-English Meaning
Isuzu's ECM reduces engine power when a critical threshold is crossed to prevent damage or emissions violations. SPN 1569 FMI 31 confirms a protection derate is active on the 4HK1 or 6HK1. The underlying reason is identified by companion codes. Resolve the companion fault to clear the derate. On Isuzu NPR, NQR, and NRR trucks, the SCR inducement system follows the same EPA-mandated counter and derate structure as other J1939-compliant engines. Isuzu IDSS displays the active inducement faults, counter distance, and aftertreatment system status. For fleet operators managing Isuzu medium-duty trucks in parcel delivery service, maintaining a DEF top-off schedule that prevents the tank from falling below 10% significantly reduces the likelihood of inducement events from DEF dosing interruption.
SPN 1569 FMI 31 is the Engine Protection Torque Derate indicator in J1939. On Isuzu 4HK1 and 6HK1 engines equipped with SCR aftertreatment (2010+ emission models), common triggers include SCR inducement from DEF depletion or quality failure, DPF critical soot loading, high coolant temperature, and oil system faults. Isuzu IDSS provides the complete active and inactive code list along with live parameter data to identify the trigger.
Common Symptoms
- Noticeable reduction in engine torque output
- Check engine or warning lamp active on the instrument cluster
- DEF or aftertreatment warning if SCR-related
- Companion codes present in IDSS
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- SCR inducement from DEF depletion or quality failure
- DPF critical soot load from repeated regeneration failures
- High coolant temperature from a cooling system fault
- Low oil pressure from a lubrication system fault
- Multiple simultaneous faults triggering the protection strategy
First Checks
- Connect Isuzu IDSS and read all active codes
- Check DEF tank level and quality
- Check coolant level and oil level immediately
- Resolve the companion code trigger before clearing SPN 1569 FMI 31
- Connect Isuzu IDSS and review the active inducement faults and counter status
- After resolving the root cause, use Isuzu IDSS to reset the SCR inducement counter
Can I Keep Driving?
With the derate active, the truck is operating with reduced power. If the trigger is a cooling or oil system fault, stop immediately. If aftertreatment-related, address the root cause before the derate deepens.
Related Codes
Related Lookup Pages
Sources
- Isuzu Commercial Trucks Service Support Isuzu Commercial Truck of America · oem · accessed 2026-06-11 · confidence medium
Source: Isuzu Commercial Truck of America, Isuzu Commercial Trucks Service Support. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Does the Isuzu NPR / NQR with the 4HK1 engine use the same inducement strategy as larger commercial trucks?
Yes. EPA 2010 and later Isuzu medium-duty trucks with the 4HK1 and 6HK1 engines use a progressive SCR inducement strategy that mirrors the approach used on Class 7 and Class 8 trucks. DEF depletion or persistent quality failure will trigger a derate, eventually limiting speed to a very low value if unaddressed.
What is the difference between the 4HK1 and 6HK1 in terms of SPN 1569 FMI 31 diagnosis?
The 4HK1 is a 5.2L four-cylinder engine and the 6HK1 is a 7.8L six-cylinder engine. The engine protection strategy and J1939 fault code architecture are the same for both. The companion codes and their resolution will vary depending on what triggered the derate, but the SPN 1569 FMI 31 diagnosis process is identical.
Can the Isuzu IDSS tool initiate a parked DPF regen on the 4HK1 or 6HK1?
Yes. Isuzu IDSS includes a forced DPF regeneration function that can initiate a parked regen when DPF soot loading is the cause of the protection derate. IDSS monitors DPF differential pressure during the regen and confirms completion.