CAT 91 Fault Code: Intake Valve Actuation Oil Pressure not responding
Intake Valve Actuation Oil Pressure not responding · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 91, SPN 2949 FMI 7, means the Intake Valve Actuation (IVA) system's control valve was cycled and the ECM saw no corresponding change in rail oil pressure. It applies to C11, C13, and C15 engines and points to a pressure sensor, control valve, debris, oil leak, or actuator problem in the IVA circuit that delays intake valve closing.
Medium severity. This code will not immediately damage the engine, but the IVA system affects valve timing and emissions performance, and an unresolved actuator or cylinder issue can lead to rougher running or further mechanical wear. Diagnose within the shift rather than ignoring it.
What does CAT error code 91 mean?
The Intake Valve Actuation (IVA) system uses pressurized engine oil to delay the closing of the intake valves, and it is controlled by the ECM. Oil flows to a rail inside the valve cover base, where a check valve keeps it from draining back into the main oil gallery, a pressure sensor reports rail pressure to the ECM, a control valve with a coil and spool opens to release oil and drop rail pressure on command, and actuators under the valve covers use that pressurized oil along with ECM signals to delay intake valve closing.
Code 91 sets when the ECM detects that the intake valve actuation pressure solenoid was cycled ten times with no resulting change in rail pressure. This tells the ECM that opening and closing the control valve is not producing the expected pressure swing in the rail, so something in the oil path, sensor, valve, or actuator is not responding correctly.
What triggers a CAT 91 code?
The ECM sets this code when the intake valve actuation pressure solenoid has been cycled 10 times with no change in intake valve actuation pressure, and only after the ECM has been powered for at least 2 seconds. This code can only occur after the engine has started, and it indicates the difference in rail pressure is incorrect while the control valve is opened and closed.
Common causes of 91
- Faulty intake valve actuation oil pressure sensor giving an inaccurate or unchanging signal
- Oil leak near the solenoids reducing available rail pressure
- Loose purge orifice allowing oil to bleed off improperly
- Failed solenoid(s) in the control valve not opening or closing as commanded
- Oil leaks under the valve cover
- Debris in the intake valve actuator system restricting oil flow or valve movement
- Failed or damaged check valve allowing oil to drain back into the main gallery
- Failed cylinder, which should be checked with a cylinder cut out test
- Improper lash settings on the intake valve actuator
- Failed intake valve actuator
- Debris inside the control valve
- One of the control valves not operating correctly
- Low engine oil level reducing available rail pressure
- A damaged or missing o-ring seal between the actuator and the cylinder head
How to troubleshoot CAT 91: first checks
- Check engine oil level first since low oil directly starves the IVA rail and is the quickest thing to rule out.
- Inspect around the valve covers and solenoids for visible oil leaks, including leaks under the valve cover itself and near the solenoid connectors.
- Check the purge orifice for looseness and confirm it is seated and torqued correctly.
- Inspect the control valve and rail for debris that could be blocking the spool or oil path.
- Check the o-ring seal between the actuator and cylinder head for damage or a missing seal.
- Verify the intake valve lash settings are within the specified adjustment for the actuator system.
- If pressure still does not respond after the above checks, consider a cylinder cut out test to isolate a failed cylinder, and inspect the check valve for damage that would let oil drain back into the main gallery.
How the code clears
No separate clearing step is listed for this code. Once the underlying cause (sensor, control valve, leak, debris, lash, or actuator problem) is repaired and the ECM sees the intake valve actuation pressure responding correctly when the solenoid is cycled, the code should not reset on the next cycle. Always confirm oil level and connector condition before assuming a part needs replacement.
Affected models and serial ranges
91 appears in our records across 3 CAT models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C11 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 91 mean?
It means SPN 2949 FMI 7, Intake Valve Actuation Oil Pressure Not Responding. The ECM cycled the IVA control valve solenoid ten times and saw no change in rail oil pressure, so it flagged the system as not responding correctly.
Which CAT engines can throw code 91?
This code applies to the C11, C13, and C15 engine models equipped with the Intake Valve Actuation system.
Can low oil cause CAT code 91?
Yes. Low engine oil level is listed as a probable cause, since the IVA rail depends on pressurized engine oil to operate the control valve and actuators.
Is it safe to keep running the engine with code 91 active?
The engine can typically keep running, but since the IVA system affects intake valve timing, it is best to diagnose the cause within the same shift rather than let it run indefinitely, especially if a failed cylinder or actuator is involved.
What parts are most often responsible for code 91?
Common culprits include the intake valve actuation oil pressure sensor, a failed or debris-blocked control valve, oil leaks near the solenoids or under the valve cover, a damaged check valve, incorrect valve lash, a missing or damaged o-ring between the actuator and cylinder head, and in some cases a failed cylinder or actuator.
How do you diagnose which component is at fault?
Start with the simple checks: oil level, visible leaks, purge orifice tightness, and connector condition. Then inspect the control valve for debris, check valve lash settings, and the o-ring seal at the actuator. A cylinder cut out test can help isolate a failed cylinder if other checks come back clean.
Does code 91 reset itself after repair?
No separate clearing step is listed. Once the root cause is fixed and the control valve produces a normal pressure change when cycled, the code should not recur on subsequent starts.