Fault code P0285 is called “Cylinder 9 Injector Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0285
This diagnostic trouble code (DTC) is a generic transmission code. Error P0285 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.
The PCM communicates and commands the fuel injectors using an internal switch called a “driver. The control module monitors each driver circuit for malfunctions.
For example, when the PCM gives a command to “turn off” a fuel injector, it expects to see high voltage in the driver circuit. Conversely, when the fuel injector receives an “on” command, it expects to see a low voltage in the driver circuit.
Code P0285 means that the engine control module has detected a low signal level in the No. 9 fuel injector circuit. The fuel injector circuit controls the fuel injectors and determines how much fuel is needed and when to spray it.
When a fuel injector fails, it causes the signal to fluctuate. This means that the engine’s operating parameters change because of mixed parameters coming into the PCM.
The control module tries to correct the situation and gives a command to reduce the fuel injector atomization, resulting in a lean mixture. The oxygen sensor then sends a lean mixture signal to the PCM. In response, the control module enriches the fuel mixture entering all cylinders. This action dramatically increases fuel consumption.
A cylinder with a faulty injector creates a lean mixture, which in turn causes higher cylinder head temperatures, resulting in detonation. The detonation sensor detects the detonation and signals the PCM, which reacts by slowing down the timing. The engine now runs intermittently, which in addition leads to a drop in power.
Symptoms of vehicle malfunctions
The main signal that an error P0285 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- Check engine control lamp on the control panel will light up (the code will be recorded in the ECM memory as a malfunction).
- Floating revolutions, vehicle engine may be unstable.
- Increased fuel consumption.
- Engine stalls or fails to start.
- Bitching/blanking ignition at idle or under load.
- Poor acceleration.
- Black smoke coming out of the tailpipe.
The severity of error P0285 is above average, caution should be exercised. Because the vehicle may have serious problems potentially affecting safety.
Factors that can cause this error code
The error code P0285 can mean that one or more of the following problems have occurred:
- Opened or short-circuited injector wires.
- Clogged fuel injector.
- Complete failure of injector.
- Wiring harness is intermittently shorted to components under the hood.
- Loose or corroded connector.
- Sometimes faulty PCM module is the cause.
How to fix or reset OBD-2 code P0285
Some suggested steps for troubleshooting and fix the error code P0285:
- Read all stored data and error codes with an OBD-II scan tool.
- Clear the error codes from the computer memory.
- Test-drive the vehicle to see if error P0285 appears again.
- Visually inspect the fuel injectors and associated wires and connectors for damage.
- Check the operation of the fuel injectors.
- If necessary, check the operation of the fuel injectors on a special test bench.
- Test the Engine Control Module (ECM).
Diagnose and repair of problems
Starting the diagnosis of fault P0285, check the battery voltage (12 V) on the injector connector wire. If there is no voltage, check for continuity to the ground using a test lamp. Connected to the plus side of the battery. If it lights up, there is a short to the ground in the voltage supply circuit.
Correct the short in the voltage supply circuit and restore proper battery voltage. Remember to check the fuse and replace it if necessary.
One injector may short out the battery voltage to all injectors.
If battery voltage is being supplied to the injector wiring harness, the next step is to turn on the light to check that the injector driver is working. Install the injector light in the injector wiring harness instead of the fuel injector. This will flash quickly when the injector driver is operating.
Check the resistance on the fuel injector if you have resistance specifications. If the resistance is above or below the rating, replace the fuel injector. If the injector passes the test, the problem is probably unstable wiring.
Remember that a fuel injector can work fine when cold, but be faulty when hot, or vice versa.
Check the wiring harness
Check the wiring harness for chafing, and the connector for loose contacts or a broken lock. If necessary, repair and check if error P0285 returns.
Disconnect the PCM connector and connect to the fuel injector driver circuit. Any resistance indicates a problem. Infinite resistance indicates a break in the circuit. Locate and repair, then try again.
If you cannot find any problems with the harness, but the fuel injector driver does not work, check the PCM power and ground. If they are OK, the PCM itself may be faulty.
If the electrical part is OK, the injector itself is probably clogged or contaminated. Try cleaning it, the flushing kit is inexpensive and will also help the other injectors work better. If flushing does not solve the problem, the injector must be replaced.
On which vehicles does this problem occur most frequently
Fault code P0285 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
Fault code P0285 can sometimes be found with other errors. The most common are the following: P0273, P0276, P0279, P0282, P0288, P0291, P0294.