What Is P0201?
P0201 is stored when the ECU detects an open circuit fault on the fuel injector circuit for cylinder 1. An open circuit means the electrical path between the ECU and the injector is broken - either through a failed injector solenoid, a broken wire, or a damaged connector. With no electrical signal, the injector cannot fire and cylinder 1 receives no fuel.
The result is a complete misfire on cylinder 1. This not only causes rough running and power loss but also sends unburnt fuel into the exhaust, which can rapidly damage the catalytic converter. P0201 should be treated urgently - do not drive long distances with this fault active.
Common Symptoms
- Severe misfire - rough, shaking engine
- Engine management light on (often flashing)
- Significant power loss
- Smell of unburnt fuel from exhaust
- Engine vibration felt through steering wheel and body
- Possible catalyst damage smell (rotten egg/sulphur)
- Fuel consumption increase
Common Causes
OBD Fault Code Plain English Guide
- 100 most common UK fault codes in plain English
- A severity rating for every code so you know what can wait
- Causes and next steps listed for each fault
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How to Diagnose P0201
Listen for Injector Click
Start the engine and use a stethoscope or long screwdriver against each injector body. A working injector clicks rapidly as it fires. No click on cylinder 1 confirms no signal is reaching the injector.
Check the Connector
Disconnect the cylinder 1 injector connector and inspect for bent pins, corrosion, or heat damage. Reseat firmly. Clear the code and retest - a poor connection can cause an intermittent open circuit.
Test Injector Resistance
With the connector unplugged, measure resistance across the two injector terminals. Most petrol injectors read 12–16 ohms; diesel injectors 0.5–2 ohms. Open circuit (infinite resistance) confirms the solenoid winding has failed.
Test Wiring Continuity
Test continuity from each pin at the injector connector back to the ECU connector. No continuity on the signal wire indicates a broken wire in the loom. Trace the harness for damage - chafing and heat damage are common near the exhaust manifold.
Swap Injectors to Confirm
To confirm the injector is faulty (not the wiring), swap cylinder 1's injector with a known-good injector from another cylinder. If the misfire moves to the other cylinder, the injector is definitely bad.
Replace the Injector
Once confirmed faulty, replace the injector. On direct-injection engines, balance the injector correction values using specialist software after replacement for smooth running.
Verdict
Test injector resistance first - open circuit means the solenoid has failed. If resistance is normal, trace the wiring for breaks. Swap injectors between cylinders to isolate the fault definitively.
P0202, P0203 and P0204 - The Same Fault, One Cylinder Over
The last digit of these codes is a map reference, not a different fault. P0201 is an open injector circuit on cylinder 1; P0202, P0203 and P0204 are exactly the same break in the circuit on cylinders 2, 3 and 4. The causes, the tests and the fixes on this page apply to all four - the only thing that changes is where you point the multimeter. One note of caution: cylinder numbering varies by manufacturer, so check which cylinder is which for your engine before condemning anything. Number 1 is usually at the crank pulley end, but "usually" has cost people injectors before.
The definitive cheap test is the swap. Move the suspect cylinder's injector connector or the injector itself to a neighbouring cylinder and clear the codes. If the fault follows the injector, the injector is your answer. If it stays on the same cylinder, the problem is the wiring between the ECU and that connector, and the injector was innocent all along.
Two or more of these codes together change the story completely. Four injectors do not fail on the same afternoon - a shared cause does. Think chafed engine loom, a corroded connector block where the harness splits, a blown injector supply feed, or in the worst case the injector driver stage in the ECU itself. Find the common point rather than testing each cylinder in isolation.
