Injection Actuation Pressure Regulator (IAPR) - Open/High
The CAT-CID165-FMI3 (Caterpillar) diesel fault code means: Injection Actuation Pressure Regulator (IAPR) - Open/High. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- advanced
- Estimated cost
- $400-$3500
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Common Symptoms
- Check Engine Light
- HEUI pressure reads 0 or default on CAT ET
- Engine may run poorly or not start
Probable Causes (Ranked by Likelihood)
- Open circuit in signal wire or connector Very Likely
- Sensor or solenoid internally open Likely
Step-by-Step Diagnostic Procedure
Connect CAT ET and confirm the active fault; note HEUI actuation pressure live value.
Inspect IAPR connector and wiring at front of engine for damage.
Measure HEUI actuation pressure with CAT ET during cranking; spec ~870 psi at cranking for start.
If pressure is low at cranking, test HP oil pump and check injector cup seals for oil loss.
Replace sensor, IAPR, or pump as indicated by tests.
Frequently Asked Questions
What does CAT code CID165-FMI3 mean?
CAT code CID165-FMI3 (Injection Actuation Pressure Regulator (IAPR) - Open/High) is a serious-severity fault in the HEUI injection system. IAPR solenoid circuit open. Engine cannot regulate HEUI pressure; injectors will not fire. HEUI (Hydraulically actuated Electronically controlled Unit Injectors) uses high-pressure engine oil to fire injectors, so HEUI faults often trace to oil pump wear, oil leaks, or sensor failures.
Can I drive with CAT CID165-FMI3?
Short distances may be possible, but plan repair soon — HEUI faults tend to progress quickly.
How much does it cost to fix CAT CID165-FMI3?
Typical cost is $400-$3500. Sensor or IAPR replacement is at the low end; high-pressure oil pump or injector work is at the high end and usually requires CAT dealer-level diagnostic time.
Sources
This page is built from documented references. Verify against your own service info before repair work.