OBD-II trouble code
P2149: Fuel Injector Group "B" Supply Voltage Circuit/Open
The useful thing about a group B fault is that a group A exists. There is a second, identical supply branch running on the same engine at the same moment, which turns every measurement into a side-by-side comparison instead of a lookup — and it is why so many of these cars arrive under their own power, running badly.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $20 – $700
- DIY difficulty
- Intermediate DIY
Browse every code in P2100–P2199, or start from the full code library.
What does P2149 mean?
P2149 reports that the positive supply feeding the injector branch the manufacturer calls group B has gone open. The letter is an index into that manufacturer's own wiring scheme rather than a description of hardware, and the fact worth pausing on is what its existence proves: this engine does not feed all of its injectors from one branch. Something about the design made a split worth engineering, and knowing why explains both how the car behaves and how to test it.
The reasons for splitting are practical. Peak current draw matters — every injector that opens simultaneously pulls from the same feed, and a single relay contact and a single wire gauge sized for eight injectors at full pulse width is heavier and hotter than two branches sized for four. Splitting also limits the damage a single fault can do, so an open branch leaves the engine running rather than dead. And on a V engine the two banks are physically separated anyway, so routing a branch to each side is simply shorter wire.
That last point produces the presentation most owners describe. Where the design splits the injectors between two branches, losing one leaves the other working, and the engine keeps running on a fraction of its cylinders. It shakes hard, has very little power, and will usually still move the car. So P2149 arrives in workshops driven in rather than towed in far more often than a total fuel-supply failure would, and the complaint is phrased as ran terrible but got me here. That is worth knowing because it changes what to expect: you are looking for the branch that is not working while the other one demonstrates, in real time, what working looks like.
Which is the strongest tool this code offers, and it exists only because there are two branches. Every measurement on the suspect branch has a known-good twin available at the same instant, on the same engine, at the same temperature, under the same load, drawing from the same battery. A reading in isolation needs a specification to be interpreted. A reading taken beside its counterpart interprets itself: put the meter on the group B supply, note the number, move to the group A supply, and the difference is the fault. No manual, no threshold, no argument about what is normal for this engine. The same applies to a relay, a fuse and a splice, if the design uses separate ones per branch — swap the components between branches and see whether the fault follows the part or stays with the wire, which is the cleanest test in electrical diagnosis and is available here for free.
One caution against assumption. There is no universal rule about which cylinders group B covers, and published tables disagree because the grouping genuinely differs between engines. Bank-based, odd and even, front and rear, firing-order pairs — all of them are in service. Do not decide which cylinders to test from a generic listing. The misfire codes stored alongside this one identify the affected cylinders directly on the car you are holding, and a wiring diagram for that specific engine identifies the branch route. Both are more reliable than a pattern borrowed from another engine family.
As for where the open lives, follow the same path as any supply fault: source first. Fuse, then relay, then the splice point where the branch separates, then the individual connectors. What differs on a two-branch engine is that each step can be compared against the equivalent step on the healthy branch, so bracketing the fault takes far fewer measurements than tracing a single circuit blind.
Common causes
- Blown fuse on the group B supply branch
- Failed relay, or a relay socket with a burnt or spread terminal, serving the second branch
- Open splice where the shared feed divides into the two injector branches
- Broken conductor in the branch wiring, often where the loom crosses between banks
- Corroded or melted supply terminal at one of the group B injector connectors
- Connector left unmated after work on the bank the branch serves
- Harness damage where the branch routes around or behind the engine to reach its cylinders
- Melted insulation from contact with an exhaust manifold, downpipe or turbo housing
- Rodent damage to the section of loom serving the affected bank
- Earlier repair splice on this branch that has corroded or pulled apart inside heat-shrink
Symptoms
- Engine runs on only part of its cylinders, shaking heavily with very little power
- Car still drives, badly, which is how most of these arrive at a workshop
- Misfire codes on a consistent set of cylinders, always the same ones
- Check engine light on and often flashing under load
- Lean code on one bank while the other bank reads normal
- Popping or backfiring on deceleration as unburnt air passes through the dead cylinders
- Engine that will not start at all if the design feeds every injector from this branch
- Fault that appeared right after work on one bank of the engine
- Strong vibration through the car at idle that does not smooth out with engine speed
- Behaviour unchanged by replacing injectors, a fuel pump or ignition components
Diagnostic steps
- 1.Read the misfire codes stored with this one and write down which cylinders they name. That set identifies group B on this engine, which no generic table can be trusted to do.
- 2.Confirm from the wiring diagram for this specific engine how the branch is routed and whether it has its own fuse and relay or shares them with the other branch.
- 3.Use the healthy branch as your reference throughout. Every voltage measurement on group B should be taken alongside the same measurement on group A at the same moment, which removes the need for any specification.
- 4.Check the fuse and relay for this branch first. If the design uses separate components per branch, swap them with the working branch's equivalents and see whether the fault follows the part.
- 5.Back-probe the supply terminal at a group B injector with the key on and compare directly against the same terminal on a group A injector. A large difference localises the fault to the branch immediately.
- 6.Work outward from the split point rather than inward from the injectors, confirming voltage at the branch point first so the open is bracketed between two known states.
- 7.Trace the branch along its physical route, paying attention to wherever it crosses between banks or passes behind the engine, since those sections take the most heat and movement.
- 8.Voltage-drop the branch under load rather than relying on a key-on static reading, because a nearly-open joint can show battery voltage with no current flowing.
- 9.Inspect the group B injector connectors for melted or pushed-out supply terminals and drag-test each pin instead of judging contact by appearance.
- 10.After the repair, confirm every previously dead cylinder now contributes, and compare the two branches under load one last time to prove the branches match.
Repair cost
$20 – $700
A fuse is a couple of dollars and a relay is $15 to $60 fitted, and on a two-branch engine those are both quick to prove by swapping with the working branch. Diagnosis is $110 to $250, and it tends to sit at the lower end here precisely because the healthy branch gives the technician a reference and cuts the guesswork. A branch wiring or splice repair runs $120 to $450 depending on how far the damaged section has to be unwrapped, and a branch that routes behind the engine to reach the far bank is the expensive version. An injector connector or terminal repair is $90 to $220. Replacing injectors costs $400 to $1,200 and does nothing about an open supply, which is the mistake this code most often provokes.
Estimate your repair
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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.