P2146 to P2149: injector group supply voltage circuit

Fuel injectors are not each wired individually back to a fuse. They are fed in groups — typically two groups on a four-cylinder engine, more on larger ones — and the ECU switches each injector’s ground.

When the supply to a whole group fails, every cylinder in that group stops firing at once.

Code	Meaning
P2146	Injector group A supply voltage circuit / open
P2147	Group A circuit low
P2148	Group A circuit high
P2149	Injector group B supply voltage circuit / open

Related: P0201 to P0206 injector circuit diagnostics.

The symptom is dramatic and the cause is often small

Half the cylinders stop firing. The engine shakes violently, may not start at all, and if it does run it does so on the remaining cylinders.

That presentation makes people fear the worst. But the cause is a supply circuit — a fuse, a relay, a connector or a wire — and those are among the cheapest things on the car.

Read the codes before drawing conclusions from the noise.

Engine misfire troubleshooting.

The grouping tells you which cylinders

Which cylinders are in which group varies by engine, and it is worth looking up for yours.

Common patterns:

• By firing order pairs — cylinders 1 and 4 in one group, 2 and 3 in the other on a four-cylinder.
• By bank on a V-engine — one group per cylinder head.

Cross-check against the misfire codes. If P2146 appears with misfire codes on exactly two cylinders, those two are group A, and the diagnosis is confirmed without opening anything.

P0301 to P0304 cylinder misfire diagnostics and P0305 to P0308 misfire cylinders 5 to 8.

Causes

The fuse

First. Injector groups are usually fused, sometimes separately. Test with a meter — a fuse can look intact and be open.

Fuses and relays basics for owners.

The relay

Many vehicles feed injectors through the main engine relay, which also feeds coils and sensors. If the injector fault comes with a crowd of unrelated codes, suspect that shared relay: P0685 to P0687 ECM power relay.

The connector

Injector connectors sit on top of a hot engine, get removed at every service that touches the intake, and their latches break. A partially seated connector is a classic intermittent.

Wiring

Chafing where the harness crosses the engine, or damage from a previous repair.

A shorted injector

An injector with a shorted winding can pull the whole group’s supply down. That is why one bad injector produces codes across several cylinders.

Measure resistance across each injector in the affected group. The one that reads far from specification is the cause.

The ECU driver

Last, and rare. Worth considering only after everything else, and worth asking whether a shorted injector damaged it.

What to check in the data

Misfire counters per cylinder are the most useful reading here.

Pattern	Meaning
Misfires on exactly the cylinders in one group	Supply fault confirmed
Misfires on all cylinders	Something shared — fuel, spark or crank signal
Misfires on one cylinder only	Individual injector, coil or compression
Zero misfires with the code stored	Intermittent — check connectors

That last row is common with supply faults, because the connection breaks momentarily and recovers.

Diagnosing intermittent faults with OBD.

Do not overlook system voltage

An engine-wide voltage problem produces injector supply codes among many others. If the code list is long and spans unrelated systems, start there: P0560 to P0563 system voltage faults.

Sequence

1. Read all codes, and map misfire codes against injector groups.
2. Check the fuse for that group with a meter.
3. Check the relay if other systems are also affected.
4. Inspect each injector connector in the affected group.
5. Measure injector resistance to find a shorted one.
6. Check system voltage if the code list is broad.
7. Consider the ECU driver last.

You can check this yourself. Pair an ELM327 adapter, open the free tier of the app and read misfire counters per cylinder. A pattern that matches an injector group exactly is a wiring diagnosis, not an engine one.