GM Duramax · Fuel Injector Group AHigh

GM Duramax P2146: Fuel Injector Group A Supply Voltage Circuit/Open

P-Code 2146 (FMI N/A) — Fuel Injector Group A Supply Voltage Circuit/Open

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Quick Answer

P2146 on the GM Duramax means the injector Group A supply voltage circuit has an open fault affecting cylinders 1–4. Check the supply fuse and harness before diagnosing individual injectors.

Overview: GM Duramax P-Code 2146

P2146 on the GM Duramax flags a loss of supply voltage to fuel injector Group A — covering cylinders 1 through 4. ProfessionalDieselRepair.com starts by checking the Group A supply fuse, which accounts for many P2146 calls and costs nothing to remedy. If the fuse is good, harness and connector integrity must be confirmed before any injectors are condemned.

Repair Snapshot

Time

1 - 3 Hours

Difficulty

Advanced

Parts Cost

$10 - $400

Dealer Labor

$300 - $800

Tools Required

  • Jaltest Diagnostic System
  • Diesel Laptops Scan Tool
  • Multimeter
  • Fuse Tester
  • Wiring Repair Kit

What P-Code 2146 Means

P2146 on the GM Duramax means the ECM has detected an open or loss of voltage in the high-side supply circuit for fuel injector Group A, which covers cylinders 1 through 4 on the LML and related Duramax engines. Unlike individual injector codes, P2146 affects all four injectors in the group — a Group A supply fault can cause a severe multi-cylinder misfire or complete loss of power on four cylinders. ProfessionalDieselRepair.com treats P2146 as a high-priority fault requiring immediate investigation of the injector driver supply fuse, relay, and wiring.

Symptoms Drivers Notice

  • Severe rough running, vibration, or multi-cylinder misfire at idle and under load
  • Check engine light on, often with reduced engine power mode
  • Cylinders 1–4 producing no RPM contribution during cut-out testing
  • Excessive black or white smoke from uncontrolled fueling in affected cylinders
  • Possible companion codes P0201, P0202, P0203, P0204 for individual cylinders in Group A

Most Likely Root Causes

Blown injector driver supply fuse for Group A

Common

An electrical spike or wiring fault can blow the Group A supply fuse, cutting power to all four injectors in the group simultaneously.

Open or damaged Group A supply wiring

Moderate

Wiring damage between the fuse box and the Group A injector connector creates an open circuit that prevents voltage from reaching the injector solenoids.

Corroded or oil-contaminated Group A harness connector

Moderate

Oil intrusion from a leaking valve cover gasket saturates the Group A connector, corroding the supply terminal and increasing circuit resistance to the point of open-circuit detection.

Failed ECM injector driver for Group A

Less Common

Internal failure of the ECM's Group A driver circuit removes the supply voltage signal from all four cylinders. This is confirmed only after the external supply circuit and harness are verified serviceable.

Common Misdiagnoses (Don't Waste Parts)

Parts-cannon replacement of four injectors based on companion P0201–P0204 codes without checking the Group A supply circuit

Why it happens: Four simultaneous injector codes suggest four failed injectors, but the actual cause is a single supply circuit fault affecting all four.

Do this instead: Always check the supply fuse and supply voltage at the Group A harness connector before condemning any injectors. Four injectors do not fail simultaneously in normal service.

Replacing individual injectors before confirming Group A supply voltage is restored

Why it happens: The injector cut-out test shows all four as non-contributing, which leads to injector replacement without verifying the supply circuit is the root cause.

Do this instead: Restore supply voltage to Group A first, clear codes, and re-run the cut-out test. If cylinders contribute normally with supply voltage restored, the injectors did not need replacement.

Master Tech Commentary

Mechanic's Notes

Shop tip: ProfessionalDieselRepair.com checks the injector driver supply fuse for Group A before doing anything else on a P2146 call. A blown fuse takes 60 seconds to find and costs nothing to replace. If the fuse blows again immediately, there is a short to ground in the Group A supply circuit — trace the harness carefully before installing another fuse. Use Jaltest to perform cylinder cut-out tests on cylinders 1–4 after the supply circuit is restored to confirm all four injectors are contributing. On LML Duramax engines, also check for oil saturation in the Group A harness connector from a leaking valve cover gasket.

Step-by-Step Diagnostic Procedure

  1. Step 1: Connect Jaltest or Diesel Laptops and confirm P2146 is stored. Check for companion codes P0201–P0204 — all four stored together with P2146 confirms a Group A supply fault rather than individual injector failures.
  2. Step 2: Locate the injector driver supply fuse for Group A in the underhood fuse box — a blown fuse is the fastest cause to confirm and the cheapest to correct. Replace with the correct amperage fuse and retest before any further diagnosis.
  3. Step 3: If the fuse is intact, use a multimeter to check for battery voltage at the Group A injector supply circuit with the key on. Loss of voltage at the connector with a good fuse confirms an open in the supply wiring between the fuse box and the injector harness.
  4. Step 4: Inspect the Group A injector wiring harness for damage, connector corrosion, or heat damage — particularly on LML engines where the harness routing near the intake manifold can be affected by oil leaks.
  5. Step 5: If supply voltage is confirmed at the harness but P2146 persists, use Jaltest to perform individual cylinder cut-out tests on cylinders 1–4. A cylinder that produces no RPM change when cut out confirms the ECM is commanding that injector with no response — pointing to an internal driver fault or severe wiring issue.

Live Data & Freeze-Frame Tips

In Jaltest or Diesel Laptops, perform an injector cylinder cut-out test on cylinders 1–4 after confirming the supply circuit is restored. Each cylinder should produce a clear RPM drop when cut out — a cylinder producing no RPM change after supply voltage is confirmed points to a failed injector or individual circuit fault. Monitor injector pulse width simultaneously; zero pulse width on all four Group A cylinders with P2146 active confirms the ECM has disabled the group due to the supply fault.

Safety Warnings

  • Never install a higher-amperage fuse to fix a repeatedly blown Group A supply fuse — a fuse blowing again after replacement confirms a short to ground that must be diagnosed before a new fuse is installed.
  • Allow the engine to cool before working on the injector harness — fuel injection components and surrounding hardware can be hot enough to cause burns.

When to Limp In vs Tow

P2146 causing a severe four-cylinder misfire or near-total power loss should not be driven under load. Have the truck towed to avoid engine damage from uncontrolled fueling imbalance.

Prevention Tips for Fleets & Owner-Operators

  • Replace the valve cover gaskets on LML Duramax engines before oil saturation reaches the injector harness connector.
  • Inspect the Group A injector supply circuit during any injector or fuel system service.
  • Address any wiring damage near the intake manifold promptly to prevent harness degradation.

Related Fault Codes

P2149

Fuel injector Group B supply voltage circuit/open — covers cylinders 5–8; P2146 and P2149 together suggest an ECM supply circuit failure.

P0201

Injector circuit open cylinder 1 — one of four companion codes that accompany P2146 when Group A supply is lost.

P0204

Injector circuit open cylinder 4 — accompanies P2146 for the final cylinder in Group A.

Frequently Asked Questions

What does P2146 mean on the GM Duramax?

P2146 means the ECM has detected an open or loss of supply voltage in the high-side circuit feeding fuel injector Group A, which powers injectors for cylinders 1 through 4. All four injectors lose their common supply voltage, causing a Group A misfire.

Why do I also have P0201, P0202, P0203, and P0204 with P2146?

These four codes appear because each individual cylinder in Group A is reporting no injector circuit activity. They are downstream symptoms of the Group A supply fault (P2146), not four separate injector failures. Resolve P2146 first.

How do I find the Group A injector supply fuse on the Duramax?

The injector driver supply fuse is in the underhood fuse and relay center. Consult the fuse box diagram in the owner's manual or Jaltest wiring data for the specific fuse location by model year. On LML Duramax trucks it is typically labeled as the injector supply or IDM fuse.

Can I drive my Duramax with P2146 active?

P2146 with four non-contributing cylinders produces severe rough running and should not be driven under load. Tow the truck to a shop to prevent engine damage from the combustion imbalance.

Is an ECM replacement needed for P2146?

Rarely — most P2146 faults are in the external supply circuit (fuse, wiring, connector), not the ECM. Only after confirming the supply circuit is sound and all four injectors test correctly should the ECM be considered.

Which scan tools diagnose P2146 on the Duramax?

Jaltest and Diesel Laptops both support GM Duramax diagnostics and can perform injector cut-out tests to confirm cylinder contribution after the supply circuit is restored. These are the preferred tools for confirming Group A supply circuit health.