EN

Severity: Moderate Code type: Generic (all makes)

P0203 Code: Injector Circuit / Open – Cylinder 3

The ECU sees no normal electrical response from injector 3: its coil, its wiring or its driver in the ECU.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Injector Circuit / Open – Cylinder 3
System
Fuel & Air Metering · Powertrain
Safe to drive?
With caution
Typical repair cost
$20–$1,600
DIY difficulty
Moderate

Cylinder 3 is the second of the two middle cylinders on an inline-four, next to cylinder 4, and with the usual 1-3-4-2 firing order it fires right after cylinder 1. P0203 means the ECU's self-check of the injector 3 circuit failed: the current or the switch-off voltage spike was missing or implausible. The code covers the whole electrical path, from the feed splice through the connector and coil to the transistor in the ECU that switches it, so it does not mean the injector is clogged. One failure pattern deserves attention: an injector whose coil develops shorted windings drops in resistance, draws extra current and can overheat its ECU driver. The code may then show up only when the engine is hot, and a replacement ECU fitted without changing that injector can fail the same way.

Can I keep driving? Usually drivable for a short, gentle trip with a three-cylinder shake. If you smell fuel, the oil level has risen or the engine is hard to crank, don't keep trying to start it, because an injector held open can flood the cylinder.

How to read P0203

How to read P0203P10223034
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 2 Fuel & air (injector circuit)
  4. 03 Specific fault

Symptoms

  • Misfire and rough running that often starts once the engine is fully warm
  • Check engine light on, usually with P0303
  • Reduced power and a stumble on acceleration
  • Code that disappears after a cold restart and returns after a long drive
  • In rare driver failures: fuel smell, hard starting and rising oil level

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Open or intermittently open coil in injector 3, often only when hot 26%
  2. Injector 3 with shorted windings, low resistance overloading its driver 18%
  3. Corroded, loose or spread terminals in the injector 3 connector 18%
  4. Harness damage between the injector 3 connector and the ECU 14%
  5. Burned-out ECU driver for injector 3, often caused by a shorted injector 12%
  6. Wrong or mismatched injector fitted during an earlier repair 7%
  7. Aftermarket wiring such as a gas conversion or tuning module in the injector 3 circuit 5%

Diagnosis step by step

Diagnostic flow: P02031Note the conditions when the codesets2Measure injector 3 cold and hot3Rule out a shorted injector beforeany ECU work4Watch the noid light carefully5Swap injector 3 with injector 46Have the driver checked on a scope

  1. Note the conditions when the code sets

    Check the freeze frame for coolant temperature and time since start. If P0203 only appears with a fully warm engine or after a long drive, suspect a coil or solder joint that opens as it expands with heat, and plan your measurements hot.

    Tools: OBD-II scanner

  2. Measure injector 3 cold and hot

    Measure across the injector pins cold, then again straight after a 20-minute drive, and compare with injectors 2 and 4. High-impedance port injectors read about 12 to 16 ohms and rise only slightly when hot. A reading that jumps to OL when warm, or sits far below its neighbors, condemns the injector.

    Tools: Multimeter

  3. Rule out a shorted injector before any ECU work

    A high-impedance injector reading, say, 5 or 6 ohms, or showing continuity from either pin to its metal body, has shorted windings. Replace it first. Fitting a new ECU while that injector stays in place risks burning out the new driver.

    Tools: Multimeter

  4. Watch the noid light carefully

    Plug a noid light into the injector 3 harness connector and crank. It should flicker. No flicker with a good feed points to the wiring or the ECU; a light that stays on solidly means the driver is stuck on, which would hold the injector open. In that case stop cranking and check the oil for fuel before the next start attempt.

    Tools: OBD-II scanner, Flashlight

  5. Swap injector 3 with injector 4

    If the injector tests borderline, exchange it with injector 4 using new seals and drive until the engine is fully hot. A code that becomes P0204 follows the injector. Cylinder 4 is the better partner than 2 because on many direct-injection ECUs cylinders 2 and 3 share a driver, which would muddy the result.

    Tools: Screwdriver, OBD-II scanner

  6. Have the driver checked on a scope

    If injector and wiring pass, a shop can look at the injector 3 control signal with an oscilloscope. A port injector normally shows a sharp switch-off spike, typically clamped somewhere around 60 to 80 V. A missing or weak spike with a good injector and wiring confirms an ECU driver fault.

    Tools: OBD-II scanner

Where the parts are

Ignition: coils and spark plugs per cylinder – P02031234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Replace injector 3 (port or direct injection) No $150–$800
Clean or repair the injector 3 connector Yes $20–$180
Repair harness between injector 3 and the ECU No $120–$400
ECU injector driver repair by a module specialist No $250–$600
Replace and program the ECU No $600–$1,600

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Field data

Ford 2 Escape, Fusion
Volkswagen 2 Tiguan Ltd

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

With P0203 active and the check engine light on, the vehicle fails an OBD-II smog inspection. If a shorted driver let fuel into the oil, change the oil after the repair; fuel-diluted oil can upset fuel trims and delay readiness.

Frequently asked questions

Why does P0203 only appear when the engine is hot?

Heat makes a cracked coil winding or a weak solder joint expand and lose contact. Measured cold, the injector looks fine. Test it straight after a long drive, or warm it carefully with a heat gun, and the open circuit usually shows up.

I replaced the ECU and P0203 came back. Why?

The most common reason is an injector 3 with shorted windings that overloaded the original driver and has now done the same to the new one. Measure the injector's resistance before fitting any further ECU.

Can a faulty injector 3 circuit flood the engine?

An open circuit starves cylinder 3 of fuel. The rarer case is a driver shorted on, which holds the injector open and pours fuel into the cylinder. Signs are a strong fuel smell, a rising oil level and hard cranking, and the engine should not be restarted until it is checked.

Does a new injector need coding?

On many diesels and some direct-injection gasoline engines, each injector has a correction code that must be entered with a scan tool after fitting. Skipping it won't cause P0203, but it can make the engine run rough or smoke.

Sources