CAT Engine 426 Fault Code: Injector Actuation Valve Short to Ground
Also called Injectior Actuation Valve Short to Ground, Injector Actuation Valve : Current Above Normal, Injector Actuation Valve Current Above Normal, Injector Actuation Valve current above normal, Injector Actuation Valve short to ground
Injector Actuation Valve Short to Ground · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 426 (SPN 42 / FMI 6) sets when the ECM detects current above the maximum threshold or a short to ground in the injection actuation pressure control valve (IAPCV) circuit on C15 and C27 engines. Expect misfire, low power, reduced rpm, or a shutdown while the code is active.
High severity. The engine can misfire, lose power, run at reduced rpm, or shut down while this code is active. It should be diagnosed before returning the machine to normal duty.
What does CAT Engine error code 426 mean?
The IAPCV is a precision displacement control actuator built into the unit injector hydraulic pump. It changes the pump's outlet flow based on a control current sent by the ECM, which lets the variable displacement pump pressurize only as much high pressure oil as the engine actually needs at that moment.
The ECM runs performance maps that define a desired actuation pressure for every operating condition. It sends a control current to the IAPCV to hit that pressure, and adjusts the current up or down if actual pressure does not match. Code 426 means the ECM sees current in this circuit above the maximum threshold, or a short circuit to ground, so it can no longer trust or control the valve properly.
Because the IAPCV governs high pressure oil delivery to the unit injectors, a fault here directly affects fuel injection timing and quantity. That's why the symptoms include misfire, low power, reduced engine speed, and possible shutdown rather than just a warning light.
What triggers a CAT Engine 426 code?
The ECM logs this code when it reads a short circuit to the IAPCV while desired current is greater than 0.2 Amps, the ECM has been powered for at least three seconds, battery voltage is greater than 9.0 VDC for two seconds, and the engine is not cranking. Once triggered, current to the IAPCV defaults to 0.0 Amps after 150 milliseconds, and the ECM attempts to re-communicate with the IAPCV at intervals of 120 milliseconds.
Common causes of 426
- Damaged, corroded, or abraded connectors or wiring in the IAPCV circuit, including pinch points in the harness
- A general problem with the wiring harness itself
- The IAPCV solenoid's resistance out of specification, or a faulty IAPCV
- A mechanical problem with the high pressure oil system, including a faulty unit injector hydraulic pump that may need replacement
- An intermittent electrical problem in the circuit
- A faulty ECM
How to troubleshoot CAT Engine 426: first checks
- Inspect all connectors in the IAPCV circuit for corrosion, moisture intrusion, or loose pins before assuming a component failure
- Trace the harness from the ECM to the unit injector hydraulic pump looking for abrasion, pinch points, or chafed insulation that could cause a short to ground
- Check battery voltage and confirm it stays above 9.0 VDC, since low or unstable voltage can affect how the ECM reads the circuit
- Pull any stored snapshot data from the ECM to see the operating conditions present when the code logged
- Test the IAPCV solenoid's resistance against specification if wiring and connectors check out
- If wiring, connectors, and the IAPCV all test good, consider a mechanical issue in the high pressure oil system or the unit injector hydraulic pump itself
How the code clears
No separate clearing step is listed beyond repairing the underlying wiring, connector, IAPCV, hydraulic pump, or ECM fault. Once the ECM detects normal current and a stable circuit, the code should stop being active, but confirm with a scan tool that it does not immediately return under load.
Affected models and serial ranges
426 appears in our records across 2 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C15 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 426 mean?
It means the ECM detected current above the maximum threshold, or a short circuit to ground, in the injection actuation pressure control valve (IAPCV) circuit. This is SPN 42, FMI 6, and affects C15 and C27 engines.
Can I keep driving or working with code 426 active?
It's not recommended. The engine may misfire, lose power, run at reduced rpm, or shut down while this code is active, so it should be diagnosed and repaired before continuing normal duty cycles.
What is the IAPCV and why does it matter?
The injection actuation pressure control valve is a precision actuator built into the unit injector hydraulic pump. It controls how much high pressure oil the pump delivers based on a current signal from the ECM, which directly affects fuel injection timing and engine performance.
What usually causes code 426?
The most common causes are damaged or corroded connectors and wiring, harness problems including pinch points, a faulty IAPCV or out-of-spec solenoid resistance, a mechanical problem with the high pressure oil system or unit injector hydraulic pump, an intermittent electrical fault, or a faulty ECM.
Does the engine shut down automatically when this code sets?
It may. The ECM defaults IAPCV current to 0.0 Amps after 150 milliseconds and retries communication every 120 milliseconds, and documented system responses include misfire, low power, reduced rpm, and engine shutdown.
Is code 426 related to low battery voltage?
The code's set conditions require battery voltage above 9.0 VDC for two seconds before it can log, so a weak or unstable battery near that threshold can be a factor in whether the fault is detected.
Do I need to replace the whole hydraulic pump for this code?
Not always. Start with wiring, connectors, and the IAPCV itself. Replacement of the unit injector hydraulic pump is listed as a possible fix only if the solenoid resistance is out of specification or there's a confirmed mechanical problem with the high pressure oil system.