OBD-II Diagnostic Trouble Code
P0612 — Fuel Injector Control Module Relay Control
P0612 means the ECM detected a fault in the circuit that controls the relay powering the fuel injector control module. The ECM commands this relay on, and it saw the control circuit open, shorted, or not matching its command.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Fuel Injector Control Module Relay Control
Code
P0612
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
What this means for truckers
P0612 (Fuel Injector Control Module Relay Control) — FICM relay control circuit fault. On Cummins X15 and similar, FICM relay fault prevents injection.
Before you replace parts — try this first
P0612 on the Fuel system is most often failed injector control module relay — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Crank and no-start, or hard start with stalling, because the injector control module may not get power. You may also get intermittent loss of power or a shutdown while driving if the relay or its circuit cuts out.
Common causes
- CommonFailed injector control module relay ($40–$200)
- OccasionalOpen or shorted relay control wire between the ECM and the relay ($120–$400)
- OccasionalCorroded relay socket or poor terminal tension in the power distribution box ($60–$300)
- RareFailed ECM relay driver ($1200–$3500)
How to fix
Swap the relay with a known-good identical relay and retest
When to use: First, quick check
Measure the relay coil resistance and the ECM control signal at the relay socket
When to use: When swapping the relay doesn't help
Check the control wire for continuity and shorts and repair it
When to use: When the command doesn't reach the relay socket
Replace the ECM
When to use: Only when the circuit is good and the ECM doesn't drive the relay
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0670 — Glow Plug Control Module Circuit
- → P0671 — Cylinder 1 Glow Plug Circuit
- → P0672 — Cylinder 2 Glow Plug Circuit
- → P0673 — Cylinder 3 Glow Plug Circuit
- → P0674 — Cylinder 4 Glow Plug Circuit
Frequently Asked Questions
Can I drive with code P0612?
Drive with caution. P0612 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P0612 on a commercial truck?
Total repair cost ranges $40–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Failed injector control module relay — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0612 fail a DOT inspection?
P0612 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0612 and related codes?
P0612 is closely related to: P0670 (Glow Plug Control Module Circuit), P0671 (Cylinder 1 Glow Plug Circuit), P0672 (Cylinder 2 Glow Plug Circuit), P0673 (Cylinder 3 Glow Plug Circuit). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0612 is set without the companions, the issue is more isolated.
How do I prevent P0612 from coming back after a repair?
For P0612 (Fuel Injector Control Module Relay Control), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.