CAT Engine 57 Fault Code: Cylinder #5 Injector : Not Responding Properly
Also called Cylinder #5 Injector - Not Responding Properly, Cylinder #5 Injector not Responding Properly, Cylinder #5 Injector not Responding Properly (C6.6 engine only), Cylinder #5 Injector not responding properly ( C6.6 engine only), Cylinder #6 Injector : Erratic, Intermittent, or Incorrect
Cylinder #5 Injector : Not Responding Properly · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 57 (SPN 655/FMI 7) means the ECM has detected that a cylinder injector, typically #5 or #6 on affected engines, is not responding properly, either from an open circuit, short circuit, or a solenoid that cannot deliver the correct fuel amount. The engine will be derated and the warning light will come on until it's resolved.
High severity. The engine is derated as soon as this code is active, and running with a bad injector risks further engine damage or fuel system contamination. Diagnose before returning to full-load operation.
What does CAT Engine error code 57 mean?
Fault code 57 points to an electronic unit injector, on cylinder #5 or #6 depending on the engine, that the ECM believes is not delivering the correct amount of fuel or is not responding to the commanded pulse. The ECM sends 105 V pulses to each injector solenoid at a specific time and duration for the current engine load and speed. When the return signal doesn't match what's expected, the ECM logs this code.
Each injector shares a power supply circuit with another injector but has its own separate return (ground) circuit back to the ECM. This means an open or short circuit can show up on either the supply or return side, and in some cases a short on a shared return line can make the ECM flag one injector while its paired injector actually keeps running fine. This is why the Injector Solenoid Test, which briefly activates each solenoid one at a time while the engine is off, is used to sort out which specific injector or wire is actually at fault.
Note that on the C175-20 engine, cylinders 9, 10, 19, and 20 do not share a power supply circuit with another cylinder. They have individual power and return circuits, which changes how a fault on those specific cylinders would present.
What triggers a CAT Engine 57 code?
This code applies to six-cylinder engines only, and is set when the electronic unit injector is no longer capable of delivering the correct amount of fuel. Once logged, the warning light comes on and the engine is derated.
Common causes of 57
- Bad or faulty injector, including internal solenoid damage or a worn injector unable to deliver correct fuel quantity
- Damaged connectors or wiring, including at the injector harness connections
- Short circuit detected on the injector power supply or return line
- Open circuit on the injector power supply or return line
- Resistance in the return wires, which can affect signal accuracy without fully failing the circuit
- Problem with the external engine wiring harness
- Problem with the ECM itself (less common, but listed as a possible cause)
- Leakage at or around the injector, which can affect solenoid cooling and operation
How to troubleshoot CAT Engine 57: first checks
- Use the electronic service tool to run the Fuel System Verification Test and confirm whether the code is still active
- Run the Injector Solenoid Test with the engine off. Each solenoid is briefly activated and should produce an audible click. The test tool will report the status as OK, Open, or Short for each one
- Inspect injector connectors and wiring harness for damage, corrosion, or looseness, especially at points exposed to engine vibration since intermittent wiring faults often only show up under vibration
- Check for resistance in the return wires and confirm the shared power supply circuit isn't affecting a paired injector
- On C175-20 engines, remember cylinders 9, 10, 19, and 20 have individual power and return circuits, not shared, when isolating the fault
- Verify 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 beyond the diagnostic procedure. If the Fuel System Verification Test still shows the code active after wiring and connector checks, the suspect electronic unit injector should be replaced. After replacing an injector, the new injector's trim code must be programmed into the ECM. If the ECM itself is replaced, all injector trim codes must be reprogrammed into the new ECM. Run the Fuel System Verification Test again afterward to confirm the fault is resolved.
Affected models and serial ranges
57 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 57 mean?
It means the ECM detected that an electronic unit injector, typically on cylinder #5 or #6, is not responding properly to the commanded fuel pulse. This can be from a wiring fault, a short or open circuit, or the injector itself failing to deliver the right amount of fuel.
Will code 57 cause the engine to lose power?
Yes. Once this code is active, the ECM will derate the engine. The warning light will also come on. Full power won't return until the underlying injector or wiring issue is fixed.
Can I keep operating the equipment with this code active?
It's not recommended. The affected injector cannot deliver the correct fuel amount, and continuing to run under derate risks further damage to the injector, fuel system, or related engine components. Diagnose it as soon as possible.
How do I tell if it's the injector or just the wiring?
Run the Injector Solenoid Test with the engine off. It briefly activates each solenoid individually and reports its status as OK, Open, or Short. This isolates whether the fault is in the injector itself or in the supply/return wiring, including cases where a short on a shared return line makes a healthy injector's partner look faulty.
Do I need to do anything special after replacing the injector?
Yes. Program the new injector's trim code into the ECM. If you also replace the ECM, every injector's trim code must be reprogrammed into it. Then rerun the Fuel System Verification Test to confirm the code clears.
Does this code apply to all CAT engines?
No. The conditions described apply specifically to six-cylinder engines, and some of the wiring detail, like the shared power supply circuits, is specific to models like the C175. Circuit layout can differ by engine, such as the C175-20's individually wired cylinders 9, 10, 19, and 20.
What's the most common cause of this fault?
Damaged connectors or wiring caused by vibration is frequently listed alongside a bad injector itself. Since wiring issues can be intermittent, a careful harness and connector inspection is worth doing before condemning the injector.