CAT Engine 35 Fault Code: Cylinder #3 Injector : Current Below Normal
Also called Cylinder #3 Injector - Current Below Normal, Cylinder #3 Injector Current Below Normal, Cylinder #3 Injector current below normal, Cylinder #3 Injector: Current Below Normal, Engine Injector Cylinder #03 : Current Below Normal
Cylinder #3 Injector : Current Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 35, SPN 653 FMI 5, means the ECM has detected a low current (open circuit) condition on the No. 3 cylinder electronic unit injector solenoid circuit or its wiring. The engine will likely run rough or lose power while the code is active. This applies to C13, C15, and C18 engines using Electronic Unit Injectors (EUI).
High severity. The engine keeps running but with low power and/or rough running, and the ECM cannot fire the affected injector while the open circuit exists. It is not an immediate shutdown condition, but ignoring it risks continued misfiring, uneven cylinder loading, and potential damage if the underlying wiring or ECM fault spreads to other cylinders that share common circuitry.
What does CAT Engine error code 35 mean?
Fault code 35 (SPN 653 FMI 5) points to the No. 3 cylinder's electronic unit injector (EUI). On these CAT engines, each injector has a solenoid mounted on top of the injector body, and the ECM sends a precisely timed voltage pulse to fire it. The ECM sends 105 v pulses to each injector solenoid at the correct time and duration for the current engine load and speed.
This code specifically means the ECM is seeing low current flow, essentially an open circuit, in the solenoid or its wiring for cylinder No. 3. The ECM does not just give up: it keeps attempting to fire the injector after logging the code, but as long as the open circuit exists, that injector cannot operate.
Because injector wiring inside the ECM is sometimes shared between cylinders, a wiring or ECM fault common to more than one injector can affect multiple cylinders at once. On four cylinder engines this common wiring can affect two injectors together, and on six cylinder engines it can affect three injectors together.
What triggers a CAT Engine 35 code?
The ECM sets this code when it detects a low current (open circuit) condition for each of five consecutive attempts to operate the injector, while battery voltage is above 9 volts DC for 2 seconds.
Common causes of 35
- Damaged, corroded, or chafed connectors and/or wiring to the No. 3 injector solenoid
- A problem within the wiring harness between the ECM and the injector connector, including an open or short circuit in the harness
- A fault in wiring common to multiple cylinders inside the ECM, which can also affect the other injector(s) sharing that circuit
- A fault between the ECM and the valve cover base connection
- A short circuit in the injector return wire
- A faulty electronic unit injector itself
- A faulty ECM
How to troubleshoot CAT Engine 35: first checks
- Bring the engine to normal operating temperature before testing, since injector solenoid faults often show up once the engine is warmed up and under vibration from heavy load
- Visually inspect the connectors and wiring at the No. 3 injector and along the harness back to the ECM for corrosion, damage, chafing, or loose pins
- Wiggle test the harness and connectors while watching for the fault to reappear, since intermittent wiring problems often only show during vibration
- Check the harness between the ECM and the injector connector for open or short circuits with the engine off and power removed
- Perform an injector cutout test: a faulty electronic unit injector will show a noticeably low reading compared to the other cylinders' injectors
- Inspect the connection at the valve cover base for the No. 3 injector circuit
- Check for a short in the injector return wire
- If wiring and connectors check out, test the injector itself, and consider ECM-side faults if the problem persists across injector swaps
How the code clears
No separate clearing step is listed. The ECM logs the code when the low current condition is detected and continues attempting to operate the injector afterward. Once the underlying wiring, connector, injector, or ECM fault is repaired and the low current condition no longer occurs, the code should stop being active on subsequent key cycles.
Affected models and serial ranges
35 appears in our records across 3 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 |
Frequently asked questions
What does CAT fault code 35 mean?
It means the ECM detected a low current, open circuit condition on the solenoid or wiring for the No. 3 cylinder electronic unit injector. This corresponds to SPN 653 FMI 5 in J1939 terms.
Can I keep running the engine with fault code 35 active?
The engine will typically keep running, but expect low power and/or rough running since the No. 3 cylinder injector cannot fire correctly while the open circuit exists. It is best diagnosed and repaired promptly rather than run indefinitely, since continued misfiring is hard on the engine and wastes fuel.
Will this code affect more than just cylinder #3?
It can. If the fault is in wiring shared inside the ECM rather than wiring unique to the No. 3 injector, other injectors sharing that same circuit can also be affected. On four cylinder engines this shared wiring can involve two injectors, and on six cylinder engines it can involve three injectors.
How do I tell if it's the injector or the wiring?
Start with a visual and physical inspection of connectors and harness for damage, corrosion, or looseness, and wiggle test them since these faults often only appear under engine vibration when warmed up. An injector cutout test can help confirm the injector itself, since a faulty unit will show a distinctly low reading compared to the other cylinders.
What voltage and timing conditions does the ECM use to set this code?
The ECM sets the code after detecting a low current condition on five consecutive attempts to fire the injector, while battery voltage stays above 9 volts DC for at least 2 seconds.
Is fault code 35 the same as a short circuit code?
No. Code 35 (SPN 653 FMI 5) specifically indicates low current from an open circuit. A high current condition, which points to a short circuit, is a separate diagnostic condition that causes the ECM to disable and periodically retry that solenoid circuit.
Which engines does this code apply to?
This code applies to CAT C13, C15, and C18 engines equipped with Electronic Unit Injectors (EUI), where each injector's solenoid is monitored individually by the ECM.