CAT Engine 26 Fault Code: Cylinder #2 Injector : Current Above Normal
Also called Cylinder #2 Injector - Current Above Normal, Cylinder #2 Injector Current Above Normal, Cylinder #2 Injector Current Below Normal, Cylinder #2 Injector Short, Cylinder #2 Injector current above normal, Cylinder #2 Injector open circuit, Cylinder #2 Injector short, Cylinder #2 Injector: Current Above Normal, Cylinder #2 Injector: Current Above Normal, Cylinder #2 Injector:Current Above Normal, Cylinder 2 Shorted, Engine Injector Cylinder #02 : Current Above Normal, Injector Cylinder 2 Short, Injector Cylinder 2 short
Cylinder #2 Injector : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 26 (SPN 652 / FMI 6) means the ECM has detected a short circuit, a high current condition, in the solenoid or wiring for the No. 2 cylinder electronic unit injector. The engine keeps running but expect low power and rough running or misfire until it's fixed.
Medium severity. The engine will keep running because the ECM keeps retrying the injector, but expect misfire, rough running, and low power. It should be diagnosed promptly to avoid drivability issues and possible damage to the ECM or injector driver circuit from a repeated short.
What does CAT Engine error code 26 mean?
>Fault code 26 is set when the Electronic Control Module (ECM) sends its firing pulse to the No. 2 cylinder's electronic unit injector solenoid and detects a short circuit (high current) in that circuit instead of a normal load. These engines use Electronic Unit Injectors (EUI) that are mechanically actuated and electronically energized. The ECM sends a 105 volt pulse to each injector solenoid at the correct time and duration for the given engine load and speed.
When the ECM sees a short, it disables that solenoid circuit for a short time, then tries again. If the short is still there, this cut-out-and-retry cycle repeats indefinitely until the fault is corrected. This protects the driver circuit but means cylinder No. 2 is not firing properly during that time, which shows up as a misfire, rough running, and reduced power.
This code is specific to No. 2 cylinder. On engines with more cylinders sharing common ECM wiring, a short in that shared wiring can also affect the other cylinders wired through the same circuit, not just No. 2.
What triggers a CAT Engine 26 code?
The ECM detects a high current (short circuit) condition for each of five consecutive attempts to operate the injector, with battery voltage above 9 volts DC for 2 seconds. If equipped, the warning light comes on and the code is logged once these conditions are met.
Common causes of 26
- Connectors, pins, or sockets for the injector circuit not fully coupled or inserted
- Corrosion, abrasion, or pinch points in the harness or wiring, including damaged connectors or wiring
- Fault or damage in the engine harness or the injector harness under the valve cover, or a fault between the ECM and the valve cover base
- A short in the return wire for the circuit
- A problem with the No. 2 cylinder itself, such as improper injector adjustment or engine valve clearance
- A faulty electronic unit injector, including internal solenoid short
- A faulty ECM, or an ECM that may need replacement
- A problem in the fuel system
How to troubleshoot CAT Engine 26: first checks
- Inspect the No. 2 cylinder injector connector and related harness connectors to confirm they are fully coupled and seated, with no corrosion or damage
- Trace the injector harness under the valve cover and the engine harness for pinch points, chafing, or corrosion that could be causing a short to ground or across the load
- Check for battery voltage conditions matching the set criteria (above 9 volts DC for 2 seconds) and confirm the fault is active and repeatable, not intermittent
- Perform an injector cutout test if you have a scan tool: a faulty injector will read low compared to the others
- Verify injector adjustment and valve clearance on cylinder No. 2 since improper adjustment is a listed cause
- Confirm the injector codes (the four digit number from each unit injector serial number) are correctly programmed into the ECM if any injector or the ECM itself was recently replaced
How the code clears
No separate clearing step is listed beyond correcting the underlying short circuit. The ECM will keep attempting to fire the injector and will keep logging the code as long as the short is present. Once the wiring, connector, or injector fault is repaired, the ECM should stop detecting the high current condition and the code should stop becoming active. If you replace an injector or the ECM, remember the injector codes must be reprogrammed or a separate code (268-02, Check Programmable Parameters) will be generated.
Affected models and serial ranges
26 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 26 mean?
It means the ECM detected a short circuit, a high current condition, in the solenoid or wiring for the No. 2 cylinder electronic unit injector. This is SPN 652 with FMI 6.
Can I keep driving or operating with code 26 active?
The engine will keep running because the ECM continues trying to fire the injector, but expect misfire, rough running, and low power. It's not an immediate stop-now situation, but it should be diagnosed soon since a cylinder isn't firing correctly.
What usually causes this short circuit?
Common causes include damaged or corroded connectors, chafed or pinched wiring in the engine or injector harness, a faulty injector solenoid, a problem specific to the No. 2 cylinder like improper valve clearance, or in some cases a faulty ECM.
Why does this fault often show up when the engine is warmed up or under load?
Faults with the injector solenoid typically occur when the engine is warmed up and under vibration from heavy loads, since heat and vibration can aggravate marginal wiring or connector issues that aren't apparent when the engine is cold or idling.
Do I need to reprogram anything after replacing 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 any injector or the ECM itself, you must reprogram the injector codes or the ECM will generate a separate code for unprogrammed parameters.
Will this affect other cylinders besides No. 2?
It can, if the short is in wiring shared with other cylinders within the ECM. On engines where cylinders share common wiring, a short in that shared circuit can affect the other cylinders wired through it, not just No. 2.
How does a scan tool help confirm this fault?
An injector cutout test lets you compare each cylinder's contribution. A faulty electronic unit injector on No. 2 will show a low reading compared to the other cylinders, helping confirm the injector itself versus a wiring issue.