OBD-II trouble code
P0273: Cylinder 5 Injector Circuit Low
The injector drive circuit for cylinder 5 is being pulled low when it should be released. The first job is not testing — it is confirming which injector is actually number 5, because it is rarely the fifth one you can see.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $50 – $1,500
- DIY difficulty
- Intermediate DIY
Browse every code in P0200–P0299, or start from the full code library.
What does P0273 mean?
Fuel injectors are not switched on their supply side. The controller feeds each injector a constant supply and fires it by momentarily connecting the other end to ground, timing the pulse to the microsecond. P0273 means the controller has detected the cylinder 5 circuit sitting low — grounded — outside the moments when it is doing the grounding itself. Something else is pulling that circuit down.
That framing matters because it points the diagnosis at exactly two possibilities and away from everything else. Either the injector winding has shorted internally, or the wire between the controller and the injector is touching ground somewhere along its run. Fuel pressure, filters, the pump and the tank are all irrelevant here — this is an electrical complaint about one specific driver circuit, and a controller that detects a shorted output will usually shut that driver down to protect itself, which is why the affected cylinder stops contributing at all.
One unplug separates the two causes. Disconnect the cylinder 5 injector and clear the code. If the complaint changes to an open-circuit fault for the same cylinder, the short was inside the injector and the harness is fine. If it still reports low with nothing connected, the injector is innocent and the fault is in the wiring between the connector and the controller. That single test is worth more than an hour of visual inspection.
Before any of that, settle which injector is cylinder 5, because this is where most money gets wasted on per-cylinder codes. Cylinder numbering follows the manufacturer's convention for the block, not the order in which parts appear when you open the bonnet. On a V6 or V8 with odd cylinders on one bank, number 5 sits on the second bank rather than being the fifth injector along, and on a transverse installation that bank may be the one against the bulkhead. The wiring diagram identifies the circuit by controller pin. Counting injectors from the front of the engine identifies the wrong one, and a perfectly good injector gets replaced.
A missing cylinder in an eight- or six-cylinder engine also means raw fuel and unburned oxygen passing into the exhaust, which loads the catalytic converter. That is why this code is marked as one to address before driving on rather than one to monitor.
Common causes
- Injector winding shorted internally, pulling the drive circuit to ground
- Injector drive wire chafed through to the block, a bracket or the manifold
- Connector contaminated with oil or coolant bridging the drive pin to ground
- Harness damage from a previous repair in the same area — intake work, valve cover gaskets, or plug changes
- Failed injector driver inside the controller, which is uncommon and diagnosed only after the harness is cleared
- Wrong injector previously fitted with a resistance far outside the specification for this system
Symptoms
- Check engine light on, often flashing under load
- Engine misfiring with a distinct dead cylinder and a rough, uneven idle
- Noticeable loss of power and poor throttle response
- Fuel smell from the exhaust and increased consumption
- Companion misfire code for cylinder 5
- Hard starting, particularly when cold
Diagnostic steps
- 1.Identify which physical injector is cylinder 5 from service data and the wiring diagram. Do not count from the front of the engine — on V configurations number 5 is usually on the second bank.
- 2.Unplug the cylinder 5 injector, clear codes and retest. A switch to an open-circuit complaint proves the injector shorted internally; a low reading that persists proves the fault is in the harness.
- 3.Measure the injector's winding resistance and compare it against specification and against the other injectors on the same engine. A reading well below its neighbours confirms a shorted winding.
- 4.Inspect the drive wire along its entire run for chafing, especially where the loom crosses brackets, the manifold or any sharp edge, and anywhere recent work has been done.
- 5.Check the connector for oil or coolant intrusion bridging the terminals, and confirm the terminals are not spread or backed out.
- 6.If the injector and harness both test good, check the drive circuit at the controller pin before concluding the driver has failed internally.
- 7.After the repair, clear codes and verify that cylinder 5 is contributing again in live data rather than relying on the light staying off.
Repair cost
$50 – $1,500
A chafed wire repaired is often $80 to $250. A single injector replaced runs roughly $150 to $500 on a port-injected engine and $350 to $900 on a direct-injection engine, where the part is dearer and the rail usually has to come off. The upper end of this range reflects a controller replacement with programming, which is the least likely outcome and should only be reached after the harness and injector have both been cleared.
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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.