Technical Description of OBD-II Trouble Code
The fuel injector circuit for Cylinder #9 is experiencing low voltage.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to vehicles equipped with OBD-II. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The OBD trouble code P0285 is a generic powertrain code that is common to all vehicles. Although the code’s reference is the same, the repair procedure may vary somewhat depending on the manufacturer.
This code indicates that the powertrain control module (PCM) has detected a low voltage situation involving the fuel injector for Cylinder #9 in the firing order.
In simple terms, this means that the fuel injector is malfunctioning for various reasons. It is important to diagnose and repair this problem as soon as possible.
When a fuel injector malfunctions, it causes changes in the engine’s operating parameters due to mixed signals at the PCM.
If the fuel injector spray pattern is reduced, it will result in a lean mixture. This sets off a chain reaction. The oxygen sensor signals a lean mixture to the PCM, which responds by enriching the fuel mixture to all cylinders. This leads to a decrease in fuel economy.
The faulty injector in the cylinder causes a lean mixture, which in turn causes a higher cylinder head temperature and detonation. The knock sensor detects the detonation and signals the PCM, which responds by retarding the timing. As a result, the engine runs rough and lacks power.
This is not the end of the ripple effect, but it gives a general idea of what happens.
Here is a cross-section diagram of a typical automotive fuel injector (provided by WikipedianProlific):
Symptoms
The symptoms associated with a P0285 code may include:
Causes
Possible causes for this DTC include:
Diagnosis / Repair
In most cases, this type of problem is caused by a loose or corroded electrical connector on the injector, a fouled injector (dirty or plugged), or a defective injector that needs to be replaced.
Based on my experience of over 45 years, loose or corroded connectors have been the most common cause of electrical faults. There have been only a few cases where low voltage wiring became shorted or open when left undisturbed.
The majority of electrical problems were related to the alternator, starter solenoid wiring, oxygen sensor wiring due to its proximity to the exhaust, and battery-related issues. Most electrical work involved correcting customer-installed items such as high-power stereos and other parts or equipment that were installed incorrectly.
The fuel injectors receive power from the fuel pump relay. The PCM activates the relay when the key is turned on, which means that the injectors have power as long as the key is on.
The PCM activates the injector by providing the necessary ground at the appropriate time and for the correct duration.
Purchase a “direct” injector flushing kit online or from an auto parts store. It will include a bottle of high-pressure injector cleaner and a hose with an end for the injector cleaner bottle to thread onto.
