CAT Engine 25355 Fault Code: Compression Brake Medium/High Solenoid #1 : Current Below Normal
Also called Compression Brake Medium/High Solenoid #1 current below normal, Compression Brake Medium/High Solenoid #1:Current Below Normal, Compression Brake Medium/High Solenoid: Current Below Normal
Compression Brake Medium/High Solenoid #1 : Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 25355 (SPN 1073 / FMI 5) sets when the engine ECM detects low current in the circuit for the Compression Brake Medium/High Solenoid #1. This is an open-circuit type fault. The engine compression brake may not activate until the fault is fixed. It affects C13, C15, C18, C27, and C32 engines equipped with engine compression brakes.
Medium severity. The engine will still run and drive normally, but auxiliary braking from the compression brake may not work. On grades or with heavy loads this reduces braking control, so it should be diagnosed before the machine goes back into service on hills or long descents.
What does CAT Engine error code 25355 mean?
The compression brake uses the engine itself to provide extra braking for the machine. It cuts down on wear to the wheel brake components, keeps brake oil temperature in check, and helps prevent engine overspeed. It also gives the operator better control of the machine, especially on grades.
Code 25355 means the ECM has detected current below normal (an open circuit condition) in the wiring for the Medium/High Solenoid #1 of the compression brake. When this happens, the engine compression brake may not activate on command, even though the rest of the engine keeps running normally.
The compression brake only works if the engine retarder configuration parameter is set to Enabled. Operation also depends on an interlock signal from the transmission ECM over the Cat Data Link confirming that engine, transmission, and machine conditions are favorable. A communication problem between the engine ECM and transmission control can also affect compression brake operation, and the transmission control will restrict operation to automatic mode while a compression brake switch fault is active.
What triggers a CAT Engine 25355 code?
In auto mode (retarder switch released), the retarder activates only when engine speed is above 2100 rpm and stays on until speed falls below 1750 rpm. In manual mode (switch actuated continuously), the retarder activates only when engine speed is above 1500 rpm and stays on until speed falls below 1400 rpm or the switch is released. The ECM logs current-low (open circuit) codes only after the Compression Brake Solenoid Test or override has been activated and then deactivated; engine speed must be zero before the overrides will function.
Common causes of 25355
- Damaged or corroded connectors and/or wiring in the compression brake circuit
- A problem in the wiring harness itself
- A faulty compression brake solenoid that needs to be replaced
- A faulty or problem compression brake switch
- An intermittent electrical problem in the circuit
- A faulty ECM that needs to be replaced (less common, checked after wiring and solenoid are ruled out)
How to troubleshoot CAT Engine 25355: first checks
- Inspect connectors and wiring for the compression brake circuit for damage, corrosion, or loose pins, since all retarder solenoids share a single return circuit and a problem there affects all of them
- Try to reproduce the fault under the same conditions it occurred, since problems with compression brake solenoids typically show up when the engine is warmed up and/or under vibration from heavy loads
- Use a diagnostic scan tool to run the Compression Brake Solenoid Test or the Compression Brake Med/High Override: activate then deactivate it to let the ECM check for open circuits, and note that engine speed must be zero for the override to function
- Check the compression brake switch for proper operation, since a faulty switch is a listed cause
- Verify the Engine Retarder Enable Command parameter is set to Enabled, since the compression brake will not operate at all if this is not configured
How the code clears
No separate clearing step is listed beyond fixing the underlying wiring, switch, or solenoid problem. The Compression Brake Solenoid Test or override must be activated and then deactivated for the ECM to properly detect and log open circuit versus short circuit conditions, so running that test as part of the repair verification is part of confirming the fix.
Affected models and serial ranges
25355 appears in our records across 5 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 25355 mean?
It means the engine ECM has detected current below normal, an open circuit condition, in the wiring for the Compression Brake Medium/High Solenoid #1. The engine compression brake may not activate as a result.
Can I still drive the machine with code 25355 active?
The engine will run normally, but the compression brake may not engage. Since this brake helps with auxiliary braking, brake wear, and controllability on grades, it is best to get it fixed before operating in situations where extra braking is needed, such as descending grades with a heavy load.
Why does this fault only show up sometimes?
Problems with compression brake solenoids typically occur when the engine is warmed up and/or under vibration from heavy loads, so an intermittent wiring or connector issue may only appear under those specific operating conditions.
What is the difference between the low current code and a high current code for this circuit?
Current low codes indicate an open circuit and are detected once the Compression Brake Solenoid Test or override is deactivated. Current high codes indicate a short circuit and are logged once the test has been activated.
Does the transmission affect the compression brake?
Yes. The transmission ECM provides an interlock control that confirms favorable engine, transmission, and machine conditions before allowing the engine ECM to control the compression brakes. A communication problem between the two ECMs can affect compression brake operation, and the transmission control will restrict operation to automatic mode while a compression brake switch fault is active.
What rpm does the compression brake activate at?
In auto mode it activates above 2100 rpm and stays on until engine speed drops below 1750 rpm. In manual mode it activates above 1500 rpm and stays on until speed drops below 1400 rpm or the retarder switch is released.
What parts are usually replaced to fix code 25355?
Repairs typically involve fixing or replacing damaged connectors and wiring in the harness, or replacing the compression brake solenoid or switch. In less common cases, if none of those resolve it, the ECM may need to be replaced.