CAT Engine 36 Fault Code: Cylinder #3 Injector : Current Above Normal
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Cylinder #3 Injector : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 36 (SPN 653, FMI 6) means the ECM has detected a short circuit, a high current condition, in the solenoid or wiring for the No. 3 cylinder electronic unit injector. The engine will keep trying to fire that injector, but expect low power and rough running until it's fixed.
Medium severity. The engine keeps running and the ECM keeps retrying the injector, so this is not an immediate shutdown situation. But rough running, misfire, and low power will persist, and repeated high-current retries can stress the ECM's driver circuit or the injector solenoid further if left unaddressed.
What does CAT Engine error code 36 mean?
Code 36 applies to engines with Electronic Unit Injectors (EUI), which are mechanically actuated and electronically energized. The ECM sends a 105 volt pulse to the No. 3 injector solenoid at the correct time and duration for the current engine load and speed. That solenoid sits on top of the injector body.
When the ECM detects a short circuit (high current) in that solenoid circuit or its wiring, it logs code 36, disables the solenoid circuit briefly, then retries it. If the short is still present, this disable-and-retry cycle repeats indefinitely until the fault is corrected. The ECM never gives up on the injector, but a short circuit means the injector can't actually fire while the fault is active.
Because the fault is specific to No. 3 cylinder's circuit, other cylinders that share common ECM wiring can also be affected: on four-cylinder engines a shared short can knock out two injectors, and on six-cylinder engines it can affect three. The practical result the operator will feel is engine misfire and low power.
What triggers a CAT Engine 36 code?
The ECM sets this code when it detects a high current condition (short circuit) on five consecutive attempts to operate the No. 3 injector solenoid, while battery voltage is above 9 volts DC for 2 seconds.
Common causes of 36
- Connectors, pins, or sockets not fully coupled or inserted at the injector or ECM
- Corrosion, abrasion, or pinch points in the harness or wiring, including damage under the valve cover
- A problem specific to the No. 3 cylinder itself, such as an open or short circuit in that cylinder's circuit
- Faulty injector or failed injector solenoid on cylinder No. 3
- Damaged or failed engine harness or valve cover base wire harness
- Short in the return wire
- Improper injector adjustment or engine valve clearance
- Fault or damage between the ECM and the valve cover base
- Faulty ECM (less common, but listed as a possible cause)
- Problem in the fuel system feeding that cylinder
How to troubleshoot CAT Engine 36: first checks
- Inspect all injector and ECM connectors for full seating, corrosion, and pin damage; reseat and clean as needed
- Trace the harness from the ECM to the No. 3 injector looking for chafe points, pinches, or abrasion, paying close attention to the section under the valve cover
- Check the injector return wire and valve cover base wiring for shorts to ground or damage
- Perform an injector cutout test if you have a scan tool: a faulty injector will show a noticeably low reading compared to the other cylinders
- Verify battery and charging voltage is stable, since the code logic checks for voltage above 9 volts DC for 2 seconds during the fault window
- Confirm injector adjustment and valve clearance are within spec, since improper adjustment is a listed cause on some engine families
- If a new injector or ECM was installed, confirm the four-digit injector codes (from the injector serial number) were reprogrammed into the ECM
How the code clears
No separate clearing step is listed. The ECM logs the code automatically and continues attempting to operate the injector after logging it. Once the short circuit is repaired, the disable-and-retry cycling should stop and the code should no longer be active on the next diagnostic check.
Affected models and serial ranges
36 appears in our records across 7 CAT Engine 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 |
| C175 | 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 fault code 36 mean?
It means the ECM detected a short circuit, a high current condition, in the solenoid or wiring for the No. 3 cylinder electronic unit injector. This is logged as SPN 653, FMI 6.
Can I keep driving or running the engine with code 36 active?
The engine will keep running because the ECM keeps retrying the injector, but expect misfire, rough running, and low power. It's not an emergency shutdown code, but it should be diagnosed promptly since one cylinder isn't firing correctly.
Why does code 36 only show up when the engine is warmed up or under load?
Problems with the injector solenoid typically show up once the engine is warmed up and under vibration from heavy loads, which is when marginal wiring or connector issues are most likely to fail intermittently.
Do I need to reprogram anything if I replace the injector?
Yes. Each unit injector has a four-digit injector code from its serial number that must be programmed into the ECM. If you replace an injector or the ECM itself, you must reprogram the injector codes or you'll trigger a separate code for unprogrammed parameters.
Could this code affect more than just cylinder No. 3?
Possibly. If the short is in wiring shared with other injectors inside the ECM, it can affect additional cylinders: two injectors on four-cylinder engines or three on six-cylinder engines that share that common wiring.
What's the difference between an open circuit code and a short circuit code like 36?
An open circuit triggers a different FMI and the ECM simply keeps trying to fire the injector without disabling it. With a short circuit (code 36's FMI 6), the ECM actively disables the solenoid circuit for a short time then retries, repeating that cycle until the short is fixed.
Is a faulty ECM a likely cause of code 36?
It's possible but less common. Most cases trace back to connectors, harness damage, or a faulty injector. ECM replacement is listed as a possible cause but should be considered only after wiring and injector checks come back clean.