|Trouble Code||Fault Location||Probable Cause|
|P0204||Injector 4 -circuit malfunction||Wiring, injector, ECM|
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What Does Code P0204 Mean?
The days of carburetors are long gone. Electronic fuel injection has been implemented in cars since the 1980s. Fuel injection offers more precise control over the fuel distribution. This results in better economy, better performance and reduced emissions.
One of the main components in a modern fuel system is the fuel injector. When the solenoid inside a fuel injector is energized, it lifts a valve off inside the injector and fuel is sprayed into the engine. Typically, there is always battery power at one of the two injector terminals. When injection is required, the powertrain control module (PCM) driver grounds the other terminal. This completes the circuit and fuel is sprayed into the cylinder.
A fuel injector
Two of the most common injector driver designs are the “saturated switch” and the “peak and hold”. With the saturated switch, maximum current is applied to the injector while it is opened (pulsed). On the other hand, the peak and hold design allows maximum current to flow just long enough to open the injector. After that, the current is reduced to the amount needed to hold the injector open.
The code P0204 stands for Injector 4 – Circuit Malfunction. This means that the PCM had detected a malfunction in the fourth injector circuit. In other words, the PCM commanded the injector on/off but did not see the subsequent change in electrical current.
An example of an injector control circuit wiring diagram
What are the common causes of code P0204 ?
To sum things up, the common causes for code P0204 are as follows:
- Failed injector
- Fault in the injector circuit
- Problem with the PCM (injector driver)
What are the symptoms of code P0204 ?
In addition to an illuminated check engine light, symptoms may include: an engine misfire, an engine that stalls and an engine that cranks but doesn’t start. Other codes, such as misfire codes, often accompany code P0204.
How do you troubleshoot code P0204 ?
The following steps will help you troubleshoot a P0204 code:
- Perform a visual inspection of the injectors and connections.
Many problems can easily be found in the harness and connectors. So, begin your diagnosis by visually inspecting the sensor and its connection.
- Check for misfires with a scan tool
First, check for other codes that would indicate cylinder misfire (P0301 – P0308). If a misfire code is present, there’s a good chance the injector fault is on that cylinder. If no misfire codes are currently stored, you can check the misfire counter PIDs (if you’ve got a capable scan tool and your car supports these parameters). These PIDs will help determine which cylinder is misfiring.
Finally, you can check for cylinder misfires using Mode $06 on your scan tool. Mode $06 gives the actual counts for misfire on each cylinder. However, the information may be presented in using reference codes you have to translate using specified tables. This is an advanced strategy best left to professionals.
- Once you’ve determined which cylinder(s) are misfiring, you can troubleshoot the injector circuit for those cylinders. The easiest way to check if the control circuit to the injector is good is by using a noid light. You simply disconnect the injector and insert the light into connector. If the noid light flashes when cranking the engine, the control circuit is functioning properly.
Testing with a noid light
If the noid light does not illuminate (or is comes on but doesn’t blink) there is a problem. Either the injector is not properly grounding the circuit, or there is no power to the injector. This can easily be checked using a simple test light. Attach one end of your test light to ground and touch the other to the B+ pin on the injector connector – the tight light should illuminate. If not, consult the factory wiring diagram and repair the power side of the circuit as necessary.
Testing power to the injector using a test light
Next, check that the PCM is properly grounding the injector. Attach one end of your test light to battery power and the other to ground side of the injector connector. When the engine is cranked, the test light should illuminate. If it does not, there is a problem with PCM or the wiring to it.
You can check for continuity between the PCM and injector using a digital multimeter set to ohms. Touch one end of the meter to the harness side of the injector connector and the other to the injector driver pin on the PCM. An over limit reading (OL) on your meter, indicates there is an open circuit between the injector and PCM. If however, you do not get an over limit reading, the PCM is likely the problem. Note: it’s important to check all injector resistance values before installing a new computer. An injector that has a resistance value outside the manufacturer’s specified range can draw too much current, damaging the driver inside the PCM.
If the circuit is OK, the next step is to test the electronic portion of the injector. This is done by measuring the resistance between its two terminals. The manufactures resistance value specifications can be found in the vehicle repair manual. Of course, an over limit reading (OL) on your meter, indicates there is an open circuit and your injector requires replacement.
Checking the injector with a digital multimeter
Sometimes, however, a static resistance test is not enough to pinpoint a bad injector. The best tool for determining injector health is a digital oscilloscope. Using a scope, you can view a waveform pattern of the injector circuit operation. By comparing the waveform on the screen to that of a known good injector, you can quickly pinpoint injector circuit faults.
Oscilloscope peak and hold injector waveform pattern
(Courtesy: Motor Age Training)
Oscilloscope saturated waveform pattern
(Courtesy: Motor Age Training)
In addition to electrical problems, injectors can experience mechanical failure and become clogged. To determine if the injectors are restricted, an injector balance test should be performed using a dedicated tester. Here’s is a good video showing how to perform an injector balance test: https://www.youtube.com/watch?v=K7STocr9FBI
Codes Related to P0204
- DTC P0201: Injector Circuit – Cylinder 1
- DTC P0202: Injector Circuit – Cylinder 2
- DTC P0203: Injector Circuit – Cylinder 3
- DTC P0205: Injector Circuit – Cylinder 5
- DTC P0206: Injector Circuit – Cylinder 6
- DTC P0207: Injector Circuit – Cylinder 7
- DTC P0208: Injector Circuit – Cylinder 8
- DTC P0209: Injector Circuit – Cylinder 9
- DTC P0210: Injector Circuit – Cylinder 10
- DTC P0211: Injector Circuit – Cylinder 11
- DTC P0212: Injector Circuit – Cylinder 12
- DTC P0213: Cold Start Injector 1
- DTC P0214: Cold Start Injector 2