CAT 36 Fault Code: Engine Injector Cylinder #03 : Current Above Normal
Engine Injector Cylinder #03 : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
CAT code 36 means the ECM detected high current flow (a short circuit) in the cylinder #03 injector solenoid circuit on C13 and C15 engines. The ECM shuts down that solenoid circuit to prevent damage and keeps trying to fire the injector periodically until the short is fixed.
High severity. The ECM disables the injector circuit to protect itself, which means cylinder #03 stops firing correctly. This causes rough running, power loss, and possible misfire damage over time. It is not an immediate stop-the-engine emergency, but it should be diagnosed promptly since the short can repeat and the cylinder is effectively out of service until fixed.
What does CAT error code 36 mean?
Code 36 is set on Electronic Unit Injector (EUI) engines where the ECM sends 105 V pulses to each injector solenoid at the correct timing and duration for engine load and speed. The ECM continuously monitors current flow through each injector solenoid circuit.
When the ECM sees high current flow on the cylinder #03 injector circuit, it interprets that as a short circuit. To protect the wiring and the ECM driver from damage, it disables that solenoid circuit. It does not give up permanently though: the ECM periodically tries to fire the injector again. If the short is still there, the code sets again and the disable cycle repeats.
This is the opposite failure mode from code 35 (Current Below Normal), which points to an open circuit or high resistance instead of a short. Code 36 always points toward a short circuit condition somewhere in the cylinder #03 injector solenoid wiring or the injector itself.
Common causes of 36
- Failed injector: the solenoid winding inside the injector itself has shorted internally.
- Wiring between the ECM and the valve cover: chafed or damaged wiring can short the injector signal wire to another powered wire or to ground.
- Wiring under the valve cover for the injector harness: this harness runs in a hot, vibration-heavy environment and insulation can wear through, causing a short between conductors.
- Plugged oil outlet port on the exhaust valve rocker arm: this is listed as a related mechanical cause tied to this code and can contribute to injector or valve train problems affecting the circuit.
How to troubleshoot CAT 36: first checks
- Run the engine to normal operating temperature before testing, since injector solenoid problems typically show up when the engine is warmed up and/or under load and vibration.
- Inspect the wiring and connectors between the ECM and the valve cover carefully for chafing, melted insulation, or pinched sections, since a short often only shows itself under vibration.
- Remove the valve cover and inspect the injector harness wiring underneath for shorts, damaged insulation, or wire-to-wire contact near cylinder #03.
- Check the oil outlet port on the exhaust valve rocker arm for cylinder #03 to confirm it is not plugged.
- Test the cylinder #03 injector solenoid itself for an internal short if the wiring and harness check out clean.
- Wiggle-test the harness and connectors while watching for the code to reset, since intermittent shorts under vibration will not always show up with the engine stationary and unloaded.
How the code clears
No separate clearing step is listed for this code. Once the short circuit in the wiring or the injector is repaired, the ECM should stop disabling the solenoid circuit and the code should stop resetting on its own as it retests the circuit periodically.
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 fault code 36 mean?
It means the ECM detected high current flow, meaning a short circuit, in the cylinder #03 injector solenoid circuit on C13 and C15 engines with electronic unit injectors. The ECM disables that circuit to protect itself and periodically retries firing the injector.
Can I keep running the engine with code 36 active?
The engine will likely run rough or lose power since cylinder #03 is not firing correctly while the circuit is disabled. It is safe to run short-term to get to a shop, but the short circuit condition should be diagnosed and fixed soon to avoid repeated cycling and potential further damage.
What is the difference between code 36 and code 35?
Code 35 is Current Below Normal, which points to an open circuit, high resistance, broken wire, or corroded connector. Code 36 is Current Above Normal, which points to a short circuit instead, such as chafed wiring shorting to another wire or an internally shorted solenoid. They require opposite diagnostic approaches: code 35 needs continuity checks, code 36 needs short-to-power or short-to-ground checks.
Why do injector wiring problems only show up sometimes?
Wiring and connector problems under the valve cover and between the ECM and valve cover often only cause a short during engine vibration, especially under heavy load when the engine is warmed up. That is why diagnostics recommend testing at normal operating temperature and wiggle-testing the harness rather than just checking it cold and stationary.
Could a plugged oil port cause this fault code?
A plugged oil outlet port on the exhaust valve rocker arm for cylinder #03 is listed as one of the causes tied to this code, alongside wiring and injector failures, so it should be checked as part of a full diagnosis even though it is a mechanical rather than electrical cause.
Is code 36 the same as code 32 (erratic injector)?
No. Code 32 covers erratic, intermittent, or incorrect behavior on the cylinder #03 injector circuit, while code 36 specifically identifies high current flow from a short circuit. They can share some of the same wiring causes but represent different failure signatures the ECM is detecting.