P026C

Fuel Injector Group A Supply Voltage Circuit Low

P026C is a generic OBD-II powertrain diagnostic trouble code: Fuel Injector Group A Supply Voltage Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P026C
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P026C means

P026C is set when the PCM detects a lower-than-expected voltage on the power supply circuit feeding injector Group A. Many V-type engines and some inline engines divide injectors into two electrically independent groups (A and B) sharing a common high-side supply voltage and individually switched low-side drivers. The PCM monitors the supply rail voltage and sets this code when Group A supply falls below the calibrated low threshold.

A low supply voltage on the injector group circuit typically indicates a wiring fault such as a short to ground on the supply wire, a failed injector power relay, a blown fuse in the injector supply circuit, or high resistance in the supply path. If multiple injectors in the group are affected simultaneously, the engine will run roughly or may not start, depending on how many cylinders are fueled by Group A.

Diagnosis should begin with checking fuses and the injector supply relay before probing wiring and individual injector driver circuits. This is primarily an electrical fault code and should be approached with circuit testing tools before replacing any injectors.

Common causes

Most-frequently reported root causes when P026C is logged.

  • 1
    Blown fuse on the Group A injector supply circuit.
  • 2
    Failed injector supply relay for Group A.
  • 3
    Short to ground in the Group A injector supply wiring harness.
  • 4
    Corroded or damaged connector on the injector supply circuit.
  • 5
    Faulty PCM power supply driver for Group A.
  • 6
    Damaged wiring harness near heat sources such as the exhaust manifold.

Symptoms drivers notice

MIL illuminated.
Rough idle or misfire on all cylinders served by injector Group A.
Possible no-start if Group A supplies a critical number of cylinders.
Engine running on fewer cylinders, causing severe vibration.
Possible reduced power or limp-mode condition.
Additional misfire DTCs for Group A cylinders.

How to diagnose P026C

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and note which cylinder misfire codes accompany P026C to confirm Group A cylinders are affected.
  2. 2
    Inspect and test the fuse for the Group A injector supply circuit.
  3. 3
    Check the injector supply relay for Group A; test for proper energization and contact function.
  4. 4
    Measure voltage at the Group A injector supply wire at the harness connector with ignition on.
  5. 5
    Inspect the wiring harness between the fuse/relay and the injector connectors for shorts to ground or damage.
  6. 6
    Check all Group A injector connectors for corrosion or spread terminals.
  7. 7
    If wiring and fuse checks pass, evaluate the PCM supply driver output.

Related powertrain codes

Frequently asked questions

How do I know which cylinders are in Group A?

Consult the vehicle-specific wiring diagram. On V6 and V8 engines, Group A typically corresponds to one bank, but this varies by manufacturer.

Can one shorted injector cause P026C?

Yes. A short to ground inside one injector in Group A can pull the entire supply rail voltage down, triggering the group-level low voltage code.

Will the engine start with P026C active?

If the voltage drop is severe enough to prevent all Group A injectors from firing, the engine may not start or will run extremely roughly on only Group B cylinders.

Is P026C an injector replacement job?

Not typically as a first step. It is primarily a circuit fault. Begin with fuses, relays, and wiring before suspecting individual injectors or the PCM.

Disabling P026C in software

RaceTune can permanently disable P026C — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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