CAT 36 Fault Code: Engine Injector Cylinder #03 : Current Above Normal
Engine Injector Cylinder #03 : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 36, SPN 653 FMI 6, means the ECM detected high current flow, a short circuit, in the cylinder #03 injector solenoid circuit on a C13 or C15 engine. The ECM disables that solenoid circuit to prevent damage but keeps periodically trying to fire the injector, repeating the fault until the short is fixed.
High severity. Cylinder #03 will misfire or run rough while this code is active, and the ECM is repeatedly cycling the disabled solenoid circuit. It will not strand the engine outright, but leaving a short circuit uncorrected risks further wiring or injector damage and ongoing performance loss.
What does CAT error code 36 mean?
SPN 653 FMI 6 tells you the ECM is monitoring the current through the injector solenoid circuit for cylinder #03 and has detected current flow that is too high, which the ECM reads as a short circuit condition.
These engines use Electronic Unit Injectors (EUI) with a solenoid in each injector. The ECM sends 105 V pulses to each solenoid at the correct time and duration for the current engine load and speed. When the ECM sees high current on the #03 circuit, it shuts that solenoid circuit off to protect it from damage caused by the high current, then periodically retries firing the injector. If the short is still present, this disable and retry cycle repeats.
This is different from a low current (open circuit) condition, which the ECM also monitors but flags separately. FMI 6 specifically points to a short circuit, not an open wire or disconnected connector.
Common causes of 36
- A failed #03 injector, most often the solenoid winding shorting internally
- Damaged or shorted wiring between the ECM and the valve cover
- Damaged or shorted wiring under the valve cover, in the injector harness itself
- A plugged oil outlet port on the exhaust valve rocker arm, which is tied to this fault on these engines
How to troubleshoot CAT 36: first checks
- Run the engine up to normal operating temperature before testing. Problems with the injector solenoid typically show up once the engine is warmed up and under load or vibration.
- With the engine warm and running, flex and inspect wiring and connectors from the ECM to the valve cover and under the valve cover at the injector harness. Look closely during vibration since intermittent shorts often only appear under load.
- Check connectors for corrosion, chafed insulation, or pinched wiring near the valve cover.
- Inspect the oil outlet port on the exhaust valve rocker arm for cylinder #03 for plugging or restriction.
- If wiring and connectors check out, test the #03 injector solenoid itself for an internal short.
How the code clears
No separate clearing step is listed for this code. Once the failed injector, damaged wiring, or plugged rocker arm oil outlet port is repaired, the ECM should stop logging the fault as it resumes normal current monitoring on the #03 solenoid circuit.
Affected models and serial ranges
36 appears in our records across 2 CAT 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 |
Frequently asked questions
What does CAT code 36 mean?
It means SPN 653 FMI 6, the ECM detected high current (a short circuit) in the cylinder #03 injector solenoid circuit on a C13 or C15 engine and disabled that circuit to prevent damage.
Will code 36 shut down my engine?
No, the ECM disables the shorted solenoid circuit but keeps periodically trying to fire the injector. The engine will keep running but cylinder #03 will likely misfire or run rough until the short is fixed.
Why does this code only show up when the engine is warm?
Problems with an injector solenoid, whether in the injector itself or the wiring, commonly surface once the engine reaches normal operating temperature and is under load or vibration, so testing cold may not reveal the fault.
What parts commonly cause this code?
A failed #03 injector, wiring between the ECM and the valve cover, wiring under the valve cover for the injector harness, or a plugged oil outlet port on the exhaust valve rocker arm for that cylinder.
How many volts does the ECM send to the injector solenoids?
The ECM sends 105 V pulses to each injector solenoid, timed and sized for the current engine load and speed.
Is a short circuit worse than an open circuit for this code?
They trigger different fault conditions. A short circuit (FMI 6, code 36) causes the ECM to disable the circuit to prevent damage, while a low current or open circuit condition is flagged separately and the ECM keeps trying to fire the injector without disabling it.