CAT 26 Fault Code: Engine Injector Cylinder #02 : Current Above Normal
Engine Injector Cylinder #02 : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
CAT code 26 (SPN 652 FMI 6) means the ECM detected high current flow, a short circuit, on the injector solenoid circuit for cylinder #02 on C13 and C15 engines. The ECM disables that solenoid circuit to prevent damage but keeps periodically trying to fire it, which causes rough running or a miss until the short is fixed.
High severity. The ECM shuts down the affected injector circuit to protect itself, which causes a running cylinder miss and possible engine damage risk if ignored. It is not an immediate stop-the-engine emergency, but it should be diagnosed promptly since the ECM keeps retrying the short and the injector or wiring can degrade further.
What does CAT error code 26 mean?
This code fires when the ECM's monitoring circuit sees high current flow (a short circuit) on the wiring that drives the injector solenoid for cylinder #02. These engines use Electronic Unit Injectors, and the ECM sends 105 V pulses to each injector solenoid at the correct timing and duration for engine load and speed.
When the ECM sees this high current condition, it disables that solenoid circuit to protect itself and the wiring from damage. It does not just give up though: the ECM will periodically attempt to fire the injector again. If the short circuit is still present, this disable-and-retry cycle repeats continuously, which shows up as a miss, rough idle, or power loss on that cylinder.
This is the 'Above Normal' current sibling of code 25, which covers the opposite failure, low current or an open circuit, on the same cylinder #02 injector solenoid circuit.
Common causes of 26
- Failed injector: an internal short inside the injector solenoid windings itself.
- Wiring between the ECM and the valve cover: chafed, pinched, or damaged harness insulation allowing the signal wire to short against another powered conductor or to ground.
- Wiring under the valve cover for the injector harness: heat, vibration, and oil exposure in this area can break down insulation and create a short at the injector connector or harness routing under the cover.
- Plugged oil outlet port on the exhaust valve rocker arm: this can allow oil or debris conditions under the valve cover that contribute to harness or connector problems in that area.
How to troubleshoot CAT 26: first checks
- Run the engine to normal operating temperature before testing. Problems with the injector solenoid circuit often only show up once the engine is warmed up and under vibration from load, so testing cold can hide the fault.
- With the engine warmed up, watch for the miss or rough running that corresponds with the ECM disabling and retrying the injector circuit for cylinder #02.
- Inspect the wiring and connectors between the ECM and the valve cover, and the injector harness wiring under the valve cover, closely for chafing, pinched insulation, or contact with other powered wires. Since these faults can be vibration-related, flex and wiggle the harness while watching for the fault to react.
- Check the oil outlet port on the exhaust valve rocker arm for the affected cylinder to confirm it is not plugged, since this can be tied to conditions under the valve cover affecting the injector harness.
- If wiring and connectors check good, test the injector solenoid itself for an internal short, since a failed injector is a listed cause.
How the code clears
No separate clearing step or reset procedure is listed for this code. Since the ECM continues to periodically retry firing the injector as long as the short circuit is present, the code will keep resetting until the underlying short in the injector, the harness between the ECM and valve cover, or the harness under the valve cover is repaired.
Affected models and serial ranges
26 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 26 mean?
It means the ECM detected high current flow (a short circuit) on the injector solenoid circuit for cylinder #02 on a C13 or C15 engine, and has disabled that circuit while it periodically retries firing the injector.
Is code 26 the same problem as code 25?
No. Code 25 covers the opposite electrical fault on the same cylinder #02 injector circuit, current below normal, meaning an open circuit or low current. Code 26 is a short circuit causing current above normal. If your symptom is a dead cylinder with no ECM retry-disable cycle, check code 25 instead.
Why does my engine only miss when it's warmed up or under load?
CAT notes that injector solenoid circuit problems typically show up once the engine reaches normal operating temperature and/or is under vibration from heavy load, since heat and vibration can expose marginal wiring or connector issues that don't appear when the engine is cold or idling.
Can I keep running the engine with this code active?
The ECM is already protecting itself by disabling the shorted solenoid circuit, but the repeated disable-and-retry cycle means you'll have a persistent miss on that cylinder. It's best to diagnose and repair the short as soon as practical rather than run indefinitely on a disabled injector.
What parts are most likely to cause this fault?
CAT lists four possible causes: a failed injector, wiring between the ECM and the valve cover, wiring under the valve cover for the injector harness, and a plugged oil outlet port on the exhaust valve rocker arm.
Where should I start looking for the short circuit?
Start with the wiring and connectors, since CAT specifically calls out paying careful attention to their condition, especially problems that only appear under vibration. Inspect from the ECM to the valve cover and then the harness routing under the valve cover before condemning the injector itself.