CAT Engine 27 Fault Code: Cylinder #2 Injector : Not Responding Properly
Also called Coolant Temperature Sensor Fault, Cylinder #2 Injector - Not Responding Properly, Cylinder #2 Injector not Responding Properly, Cylinder #2 Injector not responding properly, Cylinder #3 Injector : Erratic, Intermittent, or Incorrect
Cylinder #2 Injector : Not Responding Properly · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 27 (SPN 652 / FMI 7) on the C175 engine points to an injector solenoid, most often cylinder #2 or #3, that is not responding properly or is delivering the wrong amount of fuel. The ECM logs the code, may turn on the warning light, and will derate the engine while it keeps trying to re-energize the solenoid circuit.
High severity. The engine derates when this code is active, and continuing to run on a bad injector circuit risks further damage. Diagnose it before returning the machine to full duty.
What does CAT Engine error code 27 mean?
Fault code 27 on CAT C175 engines relates to an electronic unit injector, typically cylinder #2 or #3, that the ECM has determined is not responding properly, is erratic or intermittent, or is not delivering the correct amount of fuel.
Each injector solenoid gets power pulses from the ECM and has its own return (ground) circuit. The ECM can detect open circuits and short circuits to ground on both the supply and return sides. Because injectors share power supply pairs (except cylinders 9, 10, 19, and 20 on the C175-20, which have individual circuits), a short on one injector's return line can sometimes make the ECM flag a different injector than the one actually at fault.
When this code sets, the ECM logs the diagnostic code, may illuminate the warning light, disables the affected solenoid circuit, and periodically tries to re-energize it until the circuit is repaired. The engine will also be derated until the fault is resolved.
Common causes of 27
- Leakage in the injector or fuel system
- Damaged connectors and/or wiring, including harness damage that only shows up under vibration
- Short circuit detected on the supply or return line
- Open circuit on the supply or return line
- Problem with the ECM itself
- Problem with the wiring harness, including the injector harness under the valve cover
- Resistance in the return wires
- Low current detected in the injector solenoid circuit (logged separately as Current Above Normal for cylinder #3)
- Failed or bad injector
- External engine harness fault
How to troubleshoot CAT Engine 27: first checks
- Run the Injector Solenoid Test on the electronic service tool with the engine off. Each solenoid is briefly activated and should click audibly; the tool will report each circuit as OK, Open, or Short.
- Inspect connectors and wiring at the injector, along the harness, and under the valve cover for corrosion, chafing, or damage, especially anywhere exposed to vibration.
- Check both the power supply and return (ground) circuits for the flagged injector and its paired injector, since a short on a shared return line can make the ECM point at the wrong cylinder.
- Run the Fuel System Verification Test on the electronic service tool to confirm whether the code is still active after wiring checks.
- Verify that injector trim codes are correctly programmed into the ECM, especially after any injector or ECM replacement.
How the code clears
No separate clearing step is listed. Run the Fuel System Verification Test after any repair. If the code remains active after wiring and connector checks pass, replace the suspect electronic unit injector following the Disassembly and Assembly procedures for injector removal and installation, then run the Fuel System Verification Test again to confirm the fault has cleared.
Affected models and serial ranges
27 appears in our records across 1 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C175 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 27 mean?
It means the ECM has detected that an injector solenoid, usually on cylinder #2 or #3 of a C175 engine, is not responding properly, is behaving erratically, or cannot deliver the correct amount of fuel. This is SPN 652 / FMI 7 in the J1939 fault code system.
Will the engine keep running with code 27 active?
Yes, but it will run derated. The ECM disables the affected solenoid circuit and periodically tries to re-energize it while the fault remains, so the engine loses performance until the issue is fixed.
How do I find out if it's a wiring problem or a bad injector?
Use the electronic service tool to run the Injector Solenoid Test with the engine off. It activates each solenoid briefly and reports the circuit as OK, Open, or Short, which helps separate a wiring fault from a failed injector.
Why would the ECM point to the wrong cylinder?
Injectors share power supply circuits in pairs (except cylinders 9, 10, 19, and 20 on the C175-20). A short circuit to ground on the return line of one injector can sometimes cause the ECM to log a fault against the injector it shares a power supply with, even if that injector is fine.
Do I need to reprogram anything after replacing an injector?
Yes. Each injector has a trim code that must be programmed into the ECM when the injector is replaced. If the ECM itself is replaced, all injector trim codes need to be reprogrammed.
How do I confirm the repair fixed the fault?
After replacing the suspect injector or repairing wiring, run the Fuel System Verification Test on the electronic service tool. If the code stays active, the injector still needs to be replaced or the wiring fault has not been fully resolved.