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Error Code P0203 is defined as Cylinder 3 Injector Circuit Malfunction. This code means the PCM (powertrain control module, also known as ECM or engine control) has detected a problem in the injector or its wiring, or in injector circuit for cylinder 3.
This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II, or vehicles made in 1996 to present. Specifications in definition, troubleshooting and repairs vary from one make and/or model to another.
The PCM works by monitoring the injector, and when the latter is activated, it determines whether the voltage pulled “low” or close to zero. When the injector is switched off, the PCM expects to see a voltage close to battery voltage or “high”. If it doesn’t see what it expects to see, it detects a low or high voltage drop or resistance at injector 3, which activates the Error Code P0203. The PCM also works by monitoring the resistance circuit, and sets the code if it’s too high or too low.
Once the code is set, the vehicle will activate its failsafe mode, keeping the engine safe from further damage. The problem must be fixed before the vehicle switches back to normal operation from failsafe mode.
Error Code P0203 is quite unique, as symptoms can be felt even before the Check Engine light is activated in the dashboard, as the vehicle may display rich or lean condition alongside with engine misfire. Other common symptoms include:
- Poor acceleration and lack of power
- Engine running rough
- Engine dies or may not start at all
- Excessive fuel consumption
The most common causes for this code include:
- Defective cylinder 3 fuel injector
- Plugged or dirt in fuel injector
- Corroded fuel injector, connections or wiring
- Poor or broken electrical connections in the connector or harness
- Open or short wiring harness for the cylinder 2 injector circuit
- Defective fuel injector power circuits
How to Check
As with most error codes, qualified mechanics check this error code by hooking it up to advanced scanner and check for the codes. Codes present will have their associated freeze frame data taken, which will tell the mechanic the conditions of the vehicle when the code was set, such as engine load, vehicle speed and operating temperature.
Then, the codes will be cleared and the vehicle will be taken for test drive to see if the problem comes back and registers to the scanner. If the code indeed comes back, the mechanic will proceed on conducting a visual inspection on the injector circuit and the fuel injector itself.
Then, the mechanic will test the injector for voltage to confirm proper operation. Using the scan tool, he will then monitor injector operation, along with a noid light (installed to the injector wiring) to test for cylinder 3 injector and check for proper voltage.
If these things check out, a manufacturer specific PCM test will be performed.
How to Fix
Repairs for this error code are pretty straightforward, which will be derived from a thorough diagnosis. Possible fixes include:
- Replacement of the Cylinder 3 Fuel Injector
- Repair or replacement of any wiring issues (damaged or broken wires)
- Fixing poor connections
- Replacement of the PCM
The problem for this code ranges from just the Check Engine light in the dashboard to various poor-running conditions. Nevertheless, any code that causes the vehicle’s engine to die while running should be fixed as soon as possible, as it can be dangerous for both the vehicle and the passengers of the vehicle.
The usual suspect for this problem is the injector itself, but it always pays to conduct a thorough diagnosis before replacing it.