Code Details
| Display code | SPN 177 FMI 0 |
|---|---|
| SPN | 177 |
| FMI | 0 |
| OEM code | None listed |
| Manufacturer | Eaton |
| System | Transmission �?fluid / thermal management |
| Component | Transmission fluid / fluid cooler / temperature sensor |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
Eaton UltraShift automated manual transmissions �?including the UltraShift PLUS series �?use oil to lubricate gears and synchronizers. When fluid temperature exceeds the operating limit, shift quality degrades and internal components are at risk. SPN 177 FMI 0 is the temperature-above-normal fault. Heavy-grade climbing, extended city driving with frequent clutch engagement cycles, or a restricted cooler circuit are the primary causes. The Eaton UltraShift fluid cooler is part of the combined transmission-engine coolant circuit on most truck applications. Restricted coolant flow to the transmission cooler — from a scale-blocked cooler or a pinched coolant hose — reduces the cooler ability to remove heat from the transmission fluid. Eaton ServiceRanger records thermal event history including peak fluid temperatures and duration above the threshold, which helps distinguish a one-time high-load event from a chronic cooling system problem.
SPN 177 FMI 0 is Transmission Fluid Temperature above normal range. Eaton ServiceRanger (the OEM diagnostic tool for Eaton transmissions) displays live fluid temperature and can access thermal event history for the UltraShift TCM. ServiceRanger is available through Eaton's authorized service network.
Common Symptoms
- Transmission temperature warning or fault indicator
- Possible shift quality degradation under high-temperature conditions
- May occur after sustained mountain grades or heavy city operation
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Restricted transmission fluid cooler
- Transmission fluid past service interval
- Extreme duty cycle �?extended grade climbing or stop-and-go with heavy loads
- Fluid temperature sensor fault
- Transmission cooler coolant supply restricted from scale or debris
First Checks
- Connect Eaton ServiceRanger and monitor live transmission fluid temperature
- Check transmission fluid level and condition �?burnt-smelling or discolored fluid should be changed
- Inspect the fluid cooler for external blockage
- Confirm coolant flow to the transmission cooler is not restricted
- Review thermal event history in Eaton ServiceRanger — check peak temperature and duration
- Inspect the transmission fluid cooler coolant supply line for restriction
Can I Keep Driving?
Reduce load and allow the transmission to cool before resuming heavy operation. Continued operation at high fluid temperature accelerates wear.
Related Codes
Related Lookup Pages
Sources
- Eaton Roadranger Technical Resources — UltraShift and Advantage AMT Service Documentation Eaton Corporation (Roadranger) · oem · accessed 2026-06-11 · confidence medium
Source: Eaton Corporation (Roadranger), Eaton Roadranger Technical Resources — UltraShift and Advantage AMT Service Documentation. 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
What fluid does the Eaton UltraShift use?
Eaton UltraShift transmissions require Eaton-approved transmission fluid, typically a 50-weight mineral gear oil meeting Eaton PS-164 or equivalent for older units, and synthetic fluid for newer PLUS-generation units. Confirm the fluid specification in the Eaton maintenance guide for the specific transmission model and generation.
Does the Eaton UltraShift have an auxiliary cooler option for vocational applications?
Yes. Eaton offers an auxiliary cooler option for UltraShift transmissions in demanding duty cycles �?heavy construction, refuse, or extreme mountain grades �?where the standard cooler circuit cannot maintain acceptable fluid temperatures. An auxiliary cooler is mounted in the air stream and supplements the engine coolant-based transmission cooler.
How does SPN 177 FMI 0 differ from FMI 16 on the Eaton UltraShift?
FMI 0 indicates temperature is above normal range �?a measurement that exceeds the normal operating spec. FMI 16 indicates an above-normal moderate-severity condition on some J1939 implementations, which may represent an earlier-stage warning threshold. In practice, both FMI values indicate the transmission is running hotter than intended and require the same diagnostic approach: investigate the cooling circuit and fluid condition.