OBD-II trouble code
P2150: Fuel Injector Group "B" Supply Voltage Circuit Low
Before measuring anything, check whether the matching group A code is also stored. That single question decides whether you are looking for one fault above the point where the supply divides, or a fault on one branch below it — a relay-and-fuse job versus an hours-long trace down one leg of the harness.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $30 – $600
- DIY difficulty
- Intermediate DIY
Browse every code in P2100–P2199, or start from the full code library.
What does P2150 mean?
P2150 means the module measured the supply voltage on the injector branch it calls group B, found it below the value it expected, and stored the result. Voltage is present — this is not an open — but it is sagging, which means resistance has appeared somewhere in a circuit that is supposed to have almost none.
What makes this particular code worth a page of its own is a piece of circuit topology that most descriptions skip. Group A and group B are two branches, but they are almost never two independent circuits from the battery. In the overwhelming majority of designs they share an origin: one fused feed and one relay, which then divide at a splice or a junction into the two branches that run to their respective injectors. There is a length of wire, and a set of connections, that both branches depend on.
That shared section is what turns the scan report into a diagnostic shortcut, and it costs nothing to use. If P2150 is stored on its own, with no group A low code beside it, the fault is downstream of the split, on the group B leg alone — because a fault in the shared section would have starved both branches and both would have complained. If P2147 and P2150 are both stored, the fault is upstream of the split, in the section they have in common, and it is one repair rather than two. The scan has narrowed the search before a probe has touched a wire.
The cost difference between those two answers is large. The shared upstream section is short, accessible and made of components designed to be replaced: a fuse, a fuse holder, a relay and its socket, the main feed to it, and a splice. Pitted relay contacts are the classic finding there, because that contact carries the current for every injector on the engine each time it runs, and arcing gradually builds resistance across the faces while the relay continues to click perfectly. That is a fifteen-dollar part. A fault on the group B leg alone, by contrast, means the resistive joint is somewhere along a run of wire that goes where the injectors go — across the top of the engine, sometimes around behind it — and finding it is labour measured in hours of unwrapped loom.
The symptom follows from what low voltage does to an injector. An injector opens when the magnetic force from its winding overcomes a spring and fuel pressure, and the force depends on current, which depends on the voltage available. Below normal voltage the injector still opens, just later and less completely, so the delivered quantity falls short of what the module commanded. At idle the shortfall is small enough to be trimmed out and nothing is noticeable. Under load, with longer pulse widths and much more current drawn from the sagging feed, the shortfall becomes a real lean condition on the cylinders that branch feeds. Because only one branch is affected, that shows up as a mixture problem on one bank while the other reads normally — a stored lean code on one bank only is a strong supporting clue on this code.
One measurement discipline applies regardless of which side of the split the fault turns out to be on. The reading that matters is a voltage drop taken while current is flowing, not a resistance check on a dead circuit. A joint with a whisker of contact remaining reads fine at a few milliamps and eats several volts at twenty amps, so the test must recreate the load that provokes the fault. On a two-branch engine there is a bonus: whatever number you measure on the group B leg can be measured on the group A leg at the same instant, and the pair of readings interprets itself.
Common causes
- Relay contacts pitted from arcing in the shared feed, which starves both branches
- Corroded fuse holder or a fuse with a poor grip in the shared supply
- High resistance at the splice where the shared feed divides into the two branches
- Corroded or spread supply terminal at a group B injector connector
- Broken strands inside the group B branch wire, reducing its effective cross-section
- Earlier repair on the branch made with a poor crimp, twist joint or displacement connector
- Water and corrosion inside a connector on the affected branch
- Resistance in the module or engine ground path shifting the measured reference downward
- Battery terminal or main feed corrosion causing a whole-system sag under heavy load
- Undersized wire used to repair a section of this branch at some point in the past
Symptoms
- Hesitation or a stumble under acceleration, on a climb or while towing, with a normal idle
- Lean fuel trim or a lean code on one bank only, with the other bank reading normally
- Misfire codes that set only under load, on a consistent set of cylinders
- Brief power loss at full throttle that clears the moment the throttle is released
- Reduced fuel economy with no other obvious explanation
- Group A low supply code stored alongside this one, indicating a shared-section fault
- Harder starting when cold, when the group draws the most current
- Symptoms that reproduce at a predictable load rather than appearing at random
- Mild roughness that worsens as electrical load increases, such as with lights and fans on
- No improvement after injectors on the affected bank were replaced
Diagnostic steps
- 1.Check first whether a group A low supply code is also stored. Both codes together put the fault in the shared section upstream of the split; group B alone puts it on the group B leg below the split.
- 2.If both are stored, work only the shared section: the fuse and its holder, the relay and its socket, the main feed to the relay, and the splice where the branches divide. That is one repair, not two.
- 3.If only this code is stored, confirm the group A supply measures correctly under the same load before committing to a single-branch trace, since a marginal shared fault can trip one branch before the other.
- 4.Test by voltage drop with the circuit live and loaded. A resistance or continuity check on a dead circuit will pass the exact joint that is causing this, because neither pushes meaningful current through it.
- 5.Measure the group B and group A supplies side by side at the same instant under the same load. The comparison needs no specification and the difference between them is the fault.
- 6.Measure the drop across the relay's output contact under load rather than judging it by the click. Arced contacts switch reliably and still consume several volts at injector current.
- 7.Trace the group B branch along its physical route, giving particular attention to anywhere it crosses between banks or passes behind the engine, and flex each section while watching the meter.
- 8.Check the ground side as well as the feed. Resistance in the module or engine ground lowers the reference the supply is measured against and produces this verdict from a healthy branch.
- 9.Voltage-drop the battery terminals and main feed under load, because a whole-system sag under heavy demand can set this with the injector wiring in good condition.
- 10.Retest after the repair under the load that originally triggered it, and confirm the two branches now read the same. Clearing codes and waiting is not proof on a load-dependent fault.
Repair cost
$30 – $600
Which side of the split the fault sits on is what sets the bill, which is why reading the code pairing first is worth real money. In the shared section, a relay is $15 to $60 fitted in minutes and a fuse holder repair is $40 to $160 — and pitted relay contacts are the single most common finding there. On the group B branch alone, diagnosis is $120 to $280 and a located splice or terminal repair is $90 to $280, while a branch that has to be unwrapped along the top of the engine or traced behind it runs $250 to $500 in almost pure labour. Ground and battery terminal repairs are $40 to $150 and occasionally resolve the whole complaint. Injectors are not a repair for a sagging supply.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with engine main / powertrain relay replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.