OBD-II trouble code
P2155: Fuel Injector Group "D" Supply Voltage Circuit/Open
Four supply branches usually means more than four groups of cylinders. On engines with two injectors per cylinder — port plus direct, or petrol plus gas — a group can be an entire fuel system rather than a set of cylinders, and losing it produces a cold-start and light-load complaint with no misfire pattern at all. Find out what group D feeds before you look for dead cylinders.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $20 – $900
- DIY difficulty
- Intermediate DIY
Browse every code in P2100–P2199, or start from the full code library.
What does P2155 mean?
P2155 reports an open or loss of continuity in the positive supply to the fourth injector branch. Everything the library says about branch faults in general still applies here, but the letter D carries one piece of information the earlier letters do not: it is the last group in the generic set, and engines that use all four are unusual enough to be worth identifying before you plan any testing.
Four-branch layouts turn up in three broad situations. Large cylinder counts, where even three branches would put too many simultaneous openings on one feed. Heavy-duty and commercial diesels, where injector currents are far higher than anything in a passenger petrol engine. And — the case that changes the diagnosis completely — engines that carry two separate sets of injectors.
That third case deserves the attention. A modern petrol engine with both port and direct injection has twice as many injectors as cylinders, and the two systems are electrically different animals: the direct injectors need a high-voltage boost supply and switch enormous currents for very short periods, while the port injectors are ordinary low-current solenoids. They do not share a feed, and it would be poor design if they did. The same applies to factory or aftermarket gaseous-fuel installations, where a second rail of gas injectors sits alongside the petrol set, and to some diesels with a separate dosing or auxiliary injector.
When the fourth group is a whole system rather than a subset of cylinders, the failure looks nothing like the group A and B failures the rest of this family describes. No cylinders die, because every cylinder still has one working injector. Instead the engine loses the fuelling mode it uses in particular conditions — typically hard cold starts and poor running for the first minute, or a flat spot at light cruise, or a loss of the extra fuelling relied on under boost. There is no misfire pattern to read, which removes the single most useful diagnostic shortcut the earlier codes in this family offer, and it explains why these cars often arrive described as running fine, just not right.
So the first step is not electrical at all. Establish from the wiring diagram, or simply by looking at the engine, whether this vehicle has one injector per cylinder or two, and what group D actually supplies. That one question decides whether you should be reading misfire codes, watching fuel trims for a mode change, or looking at gas system diagnostics on a separate control unit entirely.
Once that is settled, the electrical work follows the usual path from source to load — fuse, relay or driver, distribution point, branch run, connectors — with two cautions specific to a fourth branch. It is normally the last one to leave the distribution point, so it tends to be the longest and most awkwardly routed run in the loom. And on dual-system engines, the second rail is frequently a later addition to the design or the vehicle, which means its wiring is more likely to involve added connectors, splices and routing compromises than the original injector harness beside it.
Common causes
- Open supply to a secondary injector rail on a port-plus-direct or dual-fuel engine
- Failed relay or driver dedicated to the fourth injector branch
- Blown fuse on a separately protected secondary fuel system
- Open splice or corroded stud at the distribution point where four branches divide
- Broken conductor in the longest and most awkwardly routed branch in the loom
- Damaged wiring or a disconnected plug on an aftermarket gaseous-fuel injector rail
- Corroded supply terminal at a group D injector connector
- Harness damage from heat where a late-added branch was routed near exhaust components
- Connector left unmated after fuel rail, manifold or conversion-system work
- Failed supply stage inside the control module or the secondary fuel control unit
Symptoms
- Hard or extended cold start with the engine clearing up after a minute
- Flat spot or hesitation in one particular driving condition rather than everywhere
- Loss of the extra fuelling relied on under boost, with reduced power under load
- No misfire codes at all on engines where every cylinder retains a working injector
- Check engine light with a driveability complaint that owners describe as vague
- Failure of a gaseous-fuel system to change over, with the vehicle staying on petrol
- Consistent misfire on a set of cylinders, but only on engines with one injector per cylinder
- Fuel trims that shift noticeably when the engine would normally change fuelling mode
- Increased fuel consumption with no obvious mechanical fault
- Fault that appeared after work on a secondary fuel rail or a conversion system
Diagnostic steps
- 1.Establish what group D feeds before anything else. Count the injectors on the engine: two per cylinder means a group is likely an entire fuel system, and the whole diagnostic approach changes.
- 2.If the engine carries a secondary system, check whether that system has its own control unit and its own fault memory, because the useful detail may not be in the engine module at all.
- 3.Do not expect a misfire pattern on a dual-injection engine. Every cylinder still has a working injector, so look for a lost fuelling mode instead — cold start behaviour, light-load trims, fuelling under boost.
- 4.On a single-injector-per-cylinder engine, read the misfire codes stored with this one to identify which cylinders the branch feeds, as with any other group.
- 5.Confirm from the wiring diagram whether the fourth branch has its own fuse and relay or shares them, and whether it is fed by the engine module or a separate unit.
- 6.Check the distribution point where the branches divide, paying attention to the stud or splice pack that all four share.
- 7.Trace the branch along its physical route. The fourth branch is usually the longest run and, on converted or dual-system vehicles, the one most likely to carry added connectors and splices.
- 8.On aftermarket or converted installations, inspect every added joint and plug first. Later additions to a loom fail far more often than original manufacturing joints.
- 9.Back-probe the supply at a group D injector and compare against the other branches under the same conditions.
- 10.After repair, verify the affected fuelling mode actually returns — a cold start, a light-load cruise or a changeover — rather than relying on the absence of the code.
Repair cost
$20 – $900
Diagnosis is $130 to $300 and is dominated by the first question rather than the last — identifying what the fourth group feeds is most of the work. A fuse is a few dollars and a relay $15 to $60 fitted. Repairing the distribution splice or stud is $130 to $400. A branch wiring repair is $150 to $550, and the fourth branch sits at the upper end because it tends to be the longest run in the loom. Repairing wiring on an aftermarket gaseous-fuel rail is $120 to $400 and is usually quicker because the added wiring is accessible. Connector or terminal repair is $90 to $220. A failed supply stage in the controlling module is $600 to $1,500 with programming.
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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.