P0900 code definition
This trouble code is defined as the clutch actuator circuit being open.
What the P0900 code means
When the PCM (powertrain control module) detects an open circuit in the clutch actuator control circuit, it will log a P0900 code. The PCM is constantly monitoring the output voltage of the actuator as it engages and disengages the vehicle’s clutch. In order to change gears, the PCM has to send out a command to energize the clutch actuator so it releases the clutch. After that, actuators in the transmission disengage the current gear and engage the next one (whether higher or lower).
Some models use a solenoid-type device in their actuators to operate a specific kind of clutch that uses brake fluid. Others use pneumatic actuators, hydraulic actuators, electronic sensors or some combination of these controlled by microprocessors. In any case, if this code gets reported, it’s because a circuit is left open so the PCM can’t engage a gear.
What causes the P0900 code?
There are a number of reasons that could be behind the P0900 code:
- Corrosion of the electrical connectors
- Electrical failures inside the actuator solenoids or motors
- Motion or travel sensors failing in the clutch
- Damaged wires
- Loss of ground
The problem could also be that the PCM is faulty. However, this is incredibly rare and, if the PCM was reporting codes erroneously, they wouldn’t be accompanied by the symptoms mentioned below.
What are the symptoms of the P0900 code?
The main symptom of this trouble code is simply that the vehicle won’t engage a gear. However, the issue could also spread and affect other components. Aside from a Check Engine light, these symptoms may be present too:
- The engine stalls after control system failure
- The engine doesn’t crank (this is actually a safety precaution activated by the PCM).
- The transmission enters into “limp” mode
- The transmission gets stuck in one gear, but doesn’t enter into “limp” mode
How does a mechanic diagnose the P0900 code?
A qualified mechanic will begin by using an OBD-II scanner to retrieve all the trouble codes that have been stored on a vehicle. They will then proceed to address any accompanying issues that may have come before P0900. Finally, they will need to do some combination of the following steps:
- Inspect the PCM terminal voltage
- Inspect the PCM terminal condition
- Inspect the clutch actuator circuit
- Inspect the clutch actuator harness and connector
- Inspect the clutch actuator assembly
Common mistakes when diagnosing the P0900 code
A common mistake that a lot of mechanics make is only addressing one of the above. They may fix the PCM terminal voltage problem and assume that’s the end of it when really the clutch actuator needs some attention too.
Another error is not using the OBD-II scanner because a seasoned mechanic may listen to the owner’s description of the problem and assume they know how to act. While they may address the P0900 problem, there could be others that played a role in it occurring in the first place and will do so all over again.
How serious is the P0900 code?
The code is serious insofar as the vehicle will be impossible to operate until the underlying problem gets fixed. It could also lead to a problem on the road, like the vehicle stalling out, leaving the owner stranded and in need of a tow. For this reason, even if the problem seems to go away after a minute, it’s really best to have a mechanic take a look ASAP.
What repairs can fix the P0900 code?
To fix this problem, a mechanic will do some combination of the following:
- Repair faulty wiring or connectors
- Replace PCM terminals
- Replace the clutch actuator
In very rare scenarios, the PCM may need to be replaced.
Additional comments for consideration regarding the P0900 code
As we covered earlier, there are a number of different actuators, so when addressing the P0900 code, it’s important to understand how it works and how its mechanics affect the rest of the vehicle.
Need help with a P0900 code?
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