Code Details
| Display code | SPN 177 FMI 16 |
|---|---|
| SPN | 177 |
| FMI | 16 |
| OEM code | None listed |
| Manufacturer | Eaton |
| System | Transmission �?thermal management |
| Component | Transmission fluid / cooler / temperature sensor |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-11 |
Plain-English Meaning
Eaton automated manual transmissions generate heat during heavy load operation, particularly during launch, grade operation, or prolonged low-speed loaded driving. The transmission cooler removes this heat via the engine coolant circuit. When fluid temperature exceeds the warning threshold, the TCM logs this code and may modify shift behavior to reduce heat generation.
SPN 177 is Transmission Oil Temperature in J1939. FMI 16 indicates a moderately high reading above the warning threshold. On Eaton UltraShift and Fuller Advantage transmissions, the TCM monitors fluid temperature via a sensor in the main housing. When temperature exceeds the calibrated warning point, the TCM logs the fault and may modify clutch engagement or skip-shift logic to reduce thermal load. Eaton ServiceRanger can monitor fluid temperature live and display historical temperature profiles.
Common Symptoms
- Transmission high-temperature warning on the Eaton display or dash lamp
- Possible modification of shift patterns or clutch engagement by the TCM
- Higher-than-normal temperatures during prolonged heavy-load or low-speed operation
- Fluid may smell burned if repeated overtemperature events have occurred
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Transmission fluid cooler restricted by debris or scale buildup
- Engine coolant temperature too high, reducing cooler effectiveness
- Low transmission fluid level
- Prolonged clutch slip from heavy towing on grades or poor driving technique
- Failed transmission cooler thermostat or incorrectly plumbed cooler circuit
First Checks
- Check transmission fluid level per the Eaton service manual procedure
- Inspect the transmission cooler and coolant supply lines for blockage or restrictions
- Check engine coolant temperature �?if the engine is running hot, it cannot cool the transmission fluid effectively
- Review recent operating history for prolonged heavy-grade or high-load cycles that could account for the elevated temperature
- Use Eaton ServiceRanger to monitor fluid temperature over a drive cycle
Can I Keep Driving?
At the high-temperature warning stage, the vehicle can continue operating but transmission components are at elevated risk. Avoid prolonged heavy-load operation until the cooling system is inspected. Extended high-temperature operation degrades transmission fluid and can shorten synchronizer and clutch life.
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 - Eaton UltraShift PLUS Troubleshooting Guide TRTS0940 Eaton · oem · accessed 2026-05-05 · confidence medium
Source: Eaton, Eaton UltraShift PLUS Troubleshooting Guide TRTS0940. 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 transmission fluid specification does the Eaton UltraShift require?
Eaton specifies PS-386 approved fluids for UltraShift and Fuller Advantage transmissions. This includes several synthetic and conventional transmission lubricants from major suppliers. Using a non-approved fluid can affect thermal protection and shift quality. Verify the correct specification using Eaton's fluid guide for the specific transmission model.
Can driving habits cause SPN 177 FMI 16 on an Eaton UltraShift in a vocational application?
Yes. In vocational applications such as construction or refuse trucks, frequent stops with heavy loads and high launch torque demands generate significant heat. If the cooler is sized adequately but the duty cycle is exceptionally demanding, the fluid may still reach the warning threshold during peak operation. Operating parameters within the application's rated duty cycle should not cause chronic temperature faults.
How often should the transmission fluid be changed on an Eaton UltraShift?
Eaton specifies fluid change intervals based on application and fluid type �?typically every 250,000 to 500,000 miles for approved synthetic fluids in standard applications, with shorter intervals for severe duty. High-temperature events can accelerate fluid degradation and may warrant an earlier change. Eaton ServiceRanger tracks fluid temperature history and can flag conditions that suggest the fluid has been thermally stressed.