OBD-II trouble code
P2147: Fuel Injector Group "A" Supply Voltage Circuit Low
Low is not the same as missing, and that is the whole character of this code. Voltage is arriving but sagging, so the engine behaves perfectly at idle and falls apart under load — and a continuity test will cheerfully pass the exact joint that is causing it. This one is found with a voltage-drop measurement taken while current is flowing.
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 P2147 mean?
P2147 sits between the two easy cases and is the hardest of the three supply codes to pin down. An open feed is absent voltage and produces an unmistakable failure. A shorted-to-power feed is excessive voltage and usually leaves obvious evidence. A low feed is neither: the voltage is there, the engine runs, and for most of the driving day nothing at all is wrong. What has actually happened is that the circuit has developed resistance where it should have almost none.
Resistance in a supply circuit behaves in a way that makes it slippery to diagnose, and the reason is Ohm's law rather than anything mysterious. The voltage lost across a bad joint is the product of its resistance and the current passing through it. At idle, injector pulse widths are short and the current drawn from the shared feed is small, so even a genuinely poor connection drops a fraction of a volt and everything works. Open the throttle and pulse widths lengthen across several injectors at once; current climbs sharply, and the same joint now drops several volts. The module sees the supply collapse exactly when fuel demand is highest.
That is why the complaint is so consistently described as load-related. The car idles smoothly, pulls away fine, and then hesitates, stumbles or briefly loses power on hard acceleration, up a long gradient, or when towing. Fuel trims lean out under load while reading normal at idle, and a lean code on the affected bank often appears alongside. In the worst version the module decides the supply has dropped below a usable threshold and shuts the group down as a protective measure, which turns a stumble into a momentary dead engine that recovers the instant the throttle closes.
The single most important practical point on this page is about testing method, because the wrong test actively hides this fault. A continuity check, or a resistance reading taken on a dead circuit, pushes a few milliamps through the joint. A badly corroded terminal with a whisker of metal still touching will read a satisfying beep and a fraction of an ohm under those conditions. The joint only reveals itself under real current. So the test that matters is a voltage-drop measurement: leave the circuit connected and powered, put the meter across the section you suspect while the engine is loaded, and read how much voltage that section is eating. A good supply run should lose a few tenths of a volt at most. Anything approaching a volt is a fault, and a joint dropping two or three volts is the answer.
Where those joints form is fairly predictable. The relay's own contacts are a classic, because they carry the full group current every time the engine runs and arcing slowly builds resistance across the contact faces — a relay can be visibly fine, click correctly, and still be the problem. Fuse holders develop the same condition, especially in a bay that has seen water. Crimped splices inside the loom loosen with a decade of heat cycling. Injector connector terminals spread slightly and lose contact pressure. A previous repair made with a twist-and-tape joint or an insulation-displacement connector is a strong candidate, because those never had low resistance to begin with.
One more thing separates this code from an intermittent. A genuinely intermittent circuit comes and goes at random and is maddening because it will not reproduce on command. A low-supply fault of this kind is not random at all: it reproduces reliably every time the same load is applied. That predictability is the diagnostician's advantage here, and it should be used — find the condition that brings it on, then keep the meter connected while recreating it.
Common causes
- Relay contacts pitted from arcing, adding resistance while still switching correctly
- Corroded or heat-damaged fuse holder in the injector supply circuit
- Crimped splice inside the engine loom loosened by years of heat cycling
- Spread or partly corroded supply terminal at an injector connector, losing contact pressure
- Broken strands inside an intact-looking supply wire, reducing its effective cross-section
- Poor previous repair using a twist-and-tape joint or an insulation-displacement connector
- Green corrosion inside a connector that has taken water through a failed seal
- Ground-side resistance at the module or engine ground strap, which shifts the whole reference
- Battery terminal or main power feed corrosion dragging the entire system down under load
- Undersized replacement wire used in an earlier harness repair
Symptoms
- Hesitation, stumble or a brief loss of power under hard acceleration or up a long hill
- Perfectly normal idle and normal behaviour at light throttle
- Lean fuel trim readings under load that look fine at idle
- Misfire codes on a consistent set of cylinders that only set under load
- Momentary stall or cut-out on full throttle that recovers as soon as the throttle closes
- Noticeably worse behaviour when towing or carrying a full load
- Reduced fuel economy without an obvious cause
- A lean bank code stored alongside this one
- Symptoms that reproduce reliably at the same load rather than appearing at random
- Slow or laboured cold starts where the group draws the most current
Diagnostic steps
- 1.Establish the condition that brings the fault on. This code is load-dependent and repeatable rather than random, so find the throttle position, gear and gradient that reproduces it before starting to measure.
- 2.Do not rely on a continuity test. A corroded joint with a whisker of contact left will pass continuity and pass a static resistance check, because neither passes meaningful current through it.
- 3.Perform a voltage-drop test with the circuit live and loaded. Put the meter across one section at a time while the engine is under the load that triggers the fault, and read how much voltage that section consumes.
- 4.Treat a drop of a few tenths of a volt across the whole supply run as normal, approaching a volt as a fault, and two or three volts as the answer. Work section by section to localise it.
- 5.Test the relay by measuring the drop across its output contact under load rather than by listening for the click. Arced contacts switch perfectly and still eat voltage.
- 6.Measure the drop across the fuse and its holder, which is a common site for heat and water damage and is often skipped because the fuse itself is intact.
- 7.Check the ground side as well as the supply side. Resistance in the module or engine ground shifts the reference the module measures against and produces the same low verdict from a healthy feed.
- 8.Measure battery and main feed terminal drops under load, because a whole-system voltage sag under heavy demand can set this code with nothing wrong in the injector harness at all.
- 9.Inspect any previous repair in the circuit. A twist-and-tape joint or an insulation-displacement connector never had low resistance and is a prime suspect regardless of how tidy it looks.
- 10.After the repair, retest by voltage drop under the same load that originally triggered it, rather than by clearing codes and hoping. Confirming the drop is gone is the only real proof.
Repair cost
$30 – $600
Diagnosis is $120 to $280 and is genuinely the larger part of the job on this code, because finding a resistive joint takes load testing rather than parts swapping. A relay is $15 to $60 fitted in minutes, and pitted relay contacts are one of the more common answers here. A fuse holder repair or replacement is $40 to $160. A splice or terminal repair once located is $90 to $280. Cleaning and repairing corroded battery or ground connections is $40 to $150 and sometimes fixes the whole complaint. A harness section that has to be opened along the top of the engine to reach a buried splice is the expensive case at $250 to $500, essentially all labour. Injectors are not a repair for this code.
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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.