P026D

Fuel Injector Group B Supply Voltage Circuit Low

P026D is a generic OBD-II powertrain diagnostic trouble code: Fuel Injector Group B 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
P026D
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P026D means

P026D indicates that the engine control module has determined the actual fuel injection quantity is higher than expected for the commanded conditions. It is the counterpart to P026C (quantity lower than expected) and is a fuelling-performance code, not an injector supply-voltage circuit fault. The PCM/ECM uses a fuel mass observer to track the injection correction quantity and total fuel mass over time; when delivered fuel exceeds the modelled amount beyond an allowable limit, producing an overly rich condition, this code is stored. It is most often encountered on common-rail diesel engines.

An over-delivery of fuel typically points to injectors that leak or flow too much, a fuel pressure regulator or rail pressure control fault allowing excessive pressure, or injectors whose calibration data no longer matches their true flow. Incorrectly specified replacement injectors, or sensors such as a boost or rail pressure sensor reading inaccurately, can also skew the fuelling model. Because the fault represents a genuine excess of delivered fuel rather than a broken wire, diagnosis should begin with live data comparing commanded versus actual injection quantity and rail pressure, followed by an injector balance test and a swap of the suspect injector to determine whether the fault follows the injector or stays with the channel before any part is replaced.

Common causes

Most-frequently reported root causes when P026D is logged.

  • 1
    Leaking or over-flowing fuel injector delivering excess fuel.
  • 2
    Faulty fuel pressure regulator or rail pressure control allowing high pressure.
  • 3
    Injector calibration/correction data not matching the installed injectors.
  • 4
    Incorrect or non-specified replacement injectors fitted.
  • 5
    Rail pressure or boost sensor reading inaccurately, skewing the fuelling model.
  • 6
    Sticking or contaminated injector nozzles causing uncontrolled delivery.
  • 7
    EGR or air-metering faults biasing the fuel-mass calculation.

Symptoms drivers notice

Check engine light (MIL) illuminated.
Rough idle and reduced fuel economy from an overly rich mixture.
Black smoke from the exhaust, especially on diesels.
Poor acceleration or hesitation.
Possible misfire or fuel odour.
Fouled components over time from persistent rich running.

How to diagnose P026D

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all stored and pending DTCs and record freeze-frame data before clearing.
  2. 2
    Monitor commanded versus actual injection quantity in live data while reproducing the symptom.
  3. 3
    Check fuel rail pressure at idle, cranking, and under load, and verify regulator function.
  4. 4
    Perform an injector balance or contribution test to identify an over-delivering injector.
  5. 5
    Swap the suspect injector to another cylinder to see whether the fault follows the injector.
  6. 6
    Confirm injector calibration codes match the installed injectors and that correct parts are fitted.
  7. 7
    Verify rail pressure and boost sensor accuracy before condemning the injectors or ECM.

Related powertrain codes

Frequently asked questions

What does P026D mean?

It means the ECM found the delivered fuel quantity is higher than commanded, an over-rich fuelling condition most common on diesel common-rail systems.

Is P026D a Group B supply-voltage fault?

No. Despite some databases copying that title, P026D is a fuel-injection quantity (too high) performance code, not an injector power-circuit fault.

Can a leaking injector cause P026D?

Yes. An injector that leaks or over-flows is a leading cause; an injector balance test and injector swap help confirm it.

Is it urgent to fix P026D?

It should be addressed promptly, as sustained over-fuelling wastes fuel, produces smoke and emissions, and can foul or damage components over time.

Disabling P026D in software

RaceTune can permanently disable P026D — 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.

ECU families we can disable P026D on

We hold the DaVinci A2L disable definitions for these families, so the exact P026D path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.

  • Bosch EDC17C50 verified
  • Bosch EDC17C56 verified
  • Bosch MD1CP002 verified
  • Bosch MD1CS001 verified

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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