CAT Engine 25365 Fault Code: Compression Brake Medium/High Solenoid #2 current below normal
Also called Compression Brake Medium/High Solenoid #2 : Current Below Normal, Compression Brake Medium/High Solenoid #2:Current Below Normal
Compression Brake Medium/High Solenoid #2 current below normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 25365 sets when the ECM detects low current in the circuit for the compression brake Medium/High Solenoid #2 on C27 and C32 engines. The compression brake may not activate, and the transmission control will restrict compression brake operation to automatic mode while the fault is active.
Medium severity. The engine will still run and drive normally, but auxiliary braking from the compression brake may be lost or restricted to automatic mode. On grades or with heavy loads, reduced retarder performance increases reliance on the wheel brakes, so this should be diagnosed before the next heavy-haul or downhill run.
What does CAT Engine error code 25365 mean?
The compression brake uses the engine itself to provide extra braking for the machine. It helps reduce wear on the wheel brakes, keeps brake oil temperature down, and helps prevent engine overspeed. It also improves controllability of the machine, especially on grades or under heavy load.
Code 25365 points to low current detected by the ECM in the circuit for Compression Brake Medium/High Solenoid #2. This is an electrical fault in the solenoid control circuit, not a mechanical brake failure. When this circuit reads low current, the ECM logs the fault and the engine compression brake may not activate as commanded.
The compression brake is controlled directly by the engine ECM, but the transmission ECM acts as an interlock, confirming that engine, transmission, and machine conditions are favorable before allowing compression brake operation. If there is a problem with communication between the two controls, or an active fault on the compression brake circuit, the transmission control will restrict operation to automatic mode only.
What triggers a CAT Engine 25365 code?
The ECM detects low current in the circuit for Compression Brake Medium/High Solenoid #2. Separately, related conditions describe the ECM detecting an open or a short to +Battery in the signal circuit for the compression brake, which also restricts operation to automatic mode.
Common causes of 25365
- Damaged or corroded connectors and wiring in the compression brake solenoid circuit
- A problem in the wiring harness feeding the solenoid
- A faulty compression brake solenoid
- A faulty compression brake switch
- An intermittent electrical problem in the circuit
- A faulty ECM
How to troubleshoot CAT Engine 25365: first checks
- Inspect connectors and wiring for the compression brake circuit for damage, corrosion, or loose pins, since damaged connectors and wiring are listed as the first possible cause
- Check the wiring harness routing for chafing, pinches, or heat damage, particularly near the engine where vibration under heavy loads can work connections loose over time
- Use a diagnostic scan tool to run the Compression Brake Solenoid Test or activate the Compression Brake Med/High Override to help isolate whether the problem is a short or an open circuit
- Remember all retarder solenoids share a single return circuit, so a short or open in that shared return wire will affect every compression brake solenoid, not just this one
- Verify the compression brake switch is functioning correctly, since a faulty switch is a listed possible cause
- If wiring and switch check out, suspect the compression brake solenoid itself or, if all else is confirmed good, the ECM
How the code clears
No separate clearing step is listed beyond correcting the underlying wiring, switch, solenoid, or ECM problem. When using the scan tool's Compression Brake Solenoid Test or override functions, note that the ECM only detects shorts in the circuit while the test or override is active, and only detects opens after the test or override has been activated and then deactivated. The engine speed must be at zero before the overrides will function. Reproduce the conditions under which the fault occurs, typically when the engine is warmed up and under vibration from heavy loads, to help confirm the fix.
Affected models and serial ranges
25365 appears in our records across 2 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 25365 mean?
It means the ECM detected low current in the circuit for Compression Brake Medium/High Solenoid #2. This is an electrical fault, and it can prevent the engine compression brake from activating properly.
Can I keep driving with code 25365 active?
The engine and transmission will still operate, but the compression brake may not activate, and the transmission control will restrict compression brake operation to automatic mode. Extra care is needed on grades or with heavy loads since auxiliary braking may be reduced.
Which engines does this code affect?
This code applies to CAT C27 and C32 engines equipped with an engine compression brake.
Why does the compression brake stop working intermittently?
Problems with compression brake solenoids often show up when the engine is warmed up and under vibration from heavy loads, so intermittent wiring or connector issues may only appear under those conditions.
How do technicians test the compression brake circuit for this code?
A diagnostic scan tool can run the Compression Brake Solenoid Test or activate the Compression Brake Med/High Override. Shorts are detected only while the test or override is active, while opens are detected only after the test or override is activated and then deactivated. The engine speed must be zero for the overrides to function.
Does a bad switch or wiring affect more than one solenoid?
Yes. All of the retarder solenoids share a single return circuit, so a short or open in that shared return wire can cause a problem across all the compression brake solenoids, not just the one in this code.
Is the compression brake required to be enabled for this code to matter?
Yes. The Engine Retarder Enable Command parameter must be set to Enabled for the compression brake function to operate at all, so confirm this setting as part of your diagnosis.