P0201

What the Code Means

P0201 is set by the engine control module (DME) when it detects a fault in the cylinder 1 fuel injector circuit. On N55 engines, the cause can be the wiring or the injector itself.

Normally the DME sends the injector a pulse of precisely calculated duration, and the cylinder gets an exactly metered dose of fuel. If the injector sticks open or closed, or the control circuit loses contact, the module no longer sees the expected response from the actuator and logs the fault.

Symptoms

• Check Engine light comes on;
• misfires in cylinder 1;
• rough idle;
• loss of power.

Diagnosis and Repair

Step 1. Check the Wiring and Connector

Inspect the harness and connector at the cylinder 1 injector: damaged insulation, corroded contacts, or a connector that isn't fully seated are a common cause of this fault when the injector itself is fine.

Step 2. Check Injector Resistance

Measure the injector coil resistance with a multimeter and compare it to the spec range. A reading outside that range points to a faulty injector.

Step 3. Replace the Cylinder 1 Injector

If the wiring checks out and resistance is out of spec, replace the injector. The OEM part number is 13647597801.

Step 4. Reset Adaptations

After the repair, clear the code and reset the mixture adaptations so the DME relearns from the actual condition of the new injector.

A common diagnostic mistake is replacing the injector without checking the harness and connector: with an open or corroded circuit, a new injector won't fix the problem.

Secondary Damage

• misfires in cylinder 1 mean unburned fuel burns off in the catalytic converter and damages it;
• running a cylinder with a stuck injector wears the cylinder walls.

Don't put off the repair. The longer the engine runs with active misfires, the higher the risk of expensive damage to the catalytic converter and to the pistons, rings and cylinder walls.