If you’re seeing SPN 3359 FMI 31 or DTC P088B – Transmission Filter Maintenance Required, your vehicle is warning you that the transmission filter may be restricted and needs attention. This fault is common on Allison transmissions and is designed to protect the transmission from damage caused by low or restricted fluid flow.
In this guide, you’ll learn what SPN 3359 FMI 31 means, the symptoms you’ll notice, what causes it, and how to clear the fault correctly.
What Does SPN 3359 FMI 31 (P088B) Mean?
SPN 3359 FMI 31 indicates that the Filter Life Monitor (FLM/FM) system has detected abnormal pressure conditions across the transmission filter. When the filter becomes restricted, the Transmission Control Module (TCM) triggers maintenance warnings and stores DTC P088B.
This code monitors the electrical state of the PS2 Filter Life Indicator (FLI) pressure switch. If the system detects that the PS2 switch remains pressurized even after multiple alerts, the TCM logs P088B to indicate that filter service is required.
There is no schematic available for this specific DTC.
Common Symptoms of DTC P088B
When SPN 3359 FMI 31 is active, you may notice one or more of the following:
- 🔧 SERVICE TRANS (wrench icon) flashes on the shift selector or keypad
- ⚠️ CHECK TRANS light illuminated
- The wrench icon flashes for about 2 minutes the first time Drive (D) is selected after engine start
- Fault code P088B stored in TCM history
These warnings usually appear at the next engine start when Drive is selected.
How the Filter Life Monitor System Works
The Filter Life Monitor compares:
- Main line pressure (before the filter)
- Torque Converter Clutch (TCC) lockup pressure
If the pressure difference indicates a restricted filter, the FLI pressure switch valve inside the prognostic valve body is triggered. When this condition persists, the TCM activates the SERVICE TRANS warning and stores DTC P088B.
Actions Taken When DTC P088B Sets
When this fault becomes active, the transmission system will:
- Store P088B in the TCM history for multiple ignition cycles
- Flash the SERVICE TRANS wrench icon for approximately 2 minutes after selecting Drive
- Illuminate the CHECK TRANS warning light
These alerts are intended to prompt timely filter maintenance before transmission damage occurs.
What Causes SPN 3359 FMI 31 / DTC P088B?
To accurately confirm whether the issue is a restricted filter, wiring fault, or PS2 pressure switch problem,
a professional transmission diagnostic tool with Allison support is strongly recommended.
Common causes include:
- ❌ Restricted or clogged main transmission filter (most common)
- ❌ Low TCC (lockup) pressure
- ❌ Open circuit or high resistance in W118 or W158 chassis wiring
- ❌ Open or high resistance between terminal 17 ↔ PS2 or PS2 ↔ terminal 19 in the control module harness
- ❌ Faulty PS2 pressure switch
- ❌ Internal TCM issue (rare)
How to Clear DTC P088B (SPN 3359 FMI 31)
1. Replace the Main Transmission Filter
The system is designed to automatically reset after the main filter is replaced. In most cases, this alone resolves the issue.
2. Manual Reset Methods (After Filter Replacement)
You can clear the SERVICE TRANS indicator using one of the following methods:
- Press and hold the MODE button for 10 seconds
- With ignition ON and engine OFF, shift:
N → R → N → R → N → D → N
(Pause less than 3 seconds between each shift)
3. Diagnostic Tool Reset
- Use Allison DOC to clear the DTC from TCM history
- Clear the code via SAE J1939 diagnostic message
4. Automatic Clearing
- The TCM will automatically erase the code after 40 warm-up cycles if the fault does not return
Professional Diagnostic Recommendation
If the code returns after filter replacement and reset, professional diagnostics are recommended. Using Allison DOC diagnostic software allows you to:
- Read and clear TCM fault codes accurately
- Monitor TCC lockup pressure and filter life data
- Diagnose PS2 pressure switch and wiring faults
👉 Need the right diagnostic tool for Allison transmissions? Contact our support team or explore our professional diagnostic solutions designed for heavy-duty and commercial vehicles.
Summary
- SPN 3359 FMI 31 / P088B indicates transmission filter maintenance is required
- Most cases are caused by a restricted main filter
- Replacing the filter usually clears the fault automatically
- Persistent faults may indicate wiring, pressure, or sensor issues
Addressing this warning early helps prevent transmission damage, downtime, and costly repairs.
Recommended Diagnostic Tool for SPN 3359 FMI 31
For accurate diagnosis and reset of P088B / SPN 3359 FMI 31,
we recommend using Allison DOC diagnostic software.
- ✔ Read & clear Allison TCM fault codes
- ✔ Monitor filter life & TCC lockup pressure
- ✔ Diagnose PS2 pressure switch & wiring issues
- ✔ Compatible with SAE J1939 heavy-duty vehicles
FAQs: SPN 3359 FMI 31 (P088B) – Transmission Filter Maintenance Required
What does SPN 3359 FMI 31 mean?
SPN 3359 FMI 31 is a J1939 diagnostic message that typically indicates the transmission’s Filter Life Monitor has determined the main transmission filter may be restricted and maintenance is required. On many Allison applications, this is associated with DTC P088B and a flashing SERVICE TRANS (wrench icon).
What is DTC P088B?
P088B is a transmission diagnostic trouble code that relates to the filter maintenance monitoring system. The TCM monitors the electrical state of the PS2 Filter Life Indicator (FLI) pressure switch. If the system continues to detect an abnormal pressure condition across the filter after multiple warnings, the TCM stores P088B in history and triggers visible alerts.
What symptoms will I see when P088B / SPN 3359 FMI 31 is active?
Common symptoms include a flashing SERVICE TRANS wrench icon on the shift selector (often for ~2 minutes the first time you select D after each engine start), the CHECK TRANS light, and P088B stored in TCM history.
What causes SPN 3359 FMI 31 / P088B?
The most common cause is a restricted (clogged) main transmission filter. Other causes can include low TCC (lockup) pressure, wiring issues (open/high resistance) in the chassis harness such as W118/W158, wiring faults between terminal 17 ↔ PS2 or PS2 ↔ terminal 19, a faulty PS2 pressure switch, or (rarely) a TCM issue.
Will changing the transmission filter clear P088B?
In many cases, yes. The Filter Life Monitor feature is designed to reset automatically after the main filter is replaced. If the code remains, you may need to perform a reset procedure or clear history with a diagnostic tool.
How do I reset the SERVICE TRANS (wrench icon) after changing the filter?
After replacing the main filter, you can often clear the flashing wrench icon by either holding the MODE button for 10 seconds or performing the shift sequence with ignition ON and engine OFF: N → R → N → R → N → D → N (pause less than 3 seconds between shifts). Some vehicles also support reset via a SAE J1939 message or diagnostic software.
Can I clear P088B with Allison DOC?
Yes. Allison DOC can clear P088B from the TCM history and helps confirm whether the issue is resolved by monitoring related data (like lockup pressure and filter life indicators).
How long does it take for the code to clear by itself?
If the fault does not return, the TCM may automatically clear the DTC from history after the vehicle completes 40 warm-up cycles (varies by configuration). For faster verification, most technicians clear it using a diagnostic tool after repairs.
What should I do if P088B comes back after a filter change?
If the code returns, inspect for low lockup pressure, verify the condition and operation of the PS2 pressure switch, and check for wiring opens/high resistance in the chassis/control module harness. Using a diagnostic tool such as Allison DOC can speed up pinpoint testing and reduce unnecessary parts replacement.
Is it safe to keep driving with SPN 3359 FMI 31 active?
It’s best to treat this as a maintenance-required warning and service the filter promptly. A restricted filter can reduce fluid flow and contribute to performance issues or long-term transmission wear. If additional drivability symptoms occur, stop and diagnose immediately.
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