Altezza RS200 Doesn’t Change Gears. Code P1125

It certainly can. You see, today’s transmission is an electronically sophisticated device. You’d think otherwise, but it is just not so. The transmission is controlled by or “listens” to as many as a 17 sensors and computers. In this case, though, the microcomputers that control various transmission systems are called control modules.

With that being said, though, the sensors that throttle systems that directly affect or are affected by the automatic transmission include the throttle position sensor (TPS), the mass airflow sensor (MAS) and others are affected by the throttle.

In action, when the throttle is pressed, the throttle cable puts more pressure at the bottom of the throttle valve. This, in turn, increases the line pressure that is coming from the primary regulator valve. If the pressure does not continue increasing when the throttle is pushed, it means that the line pressure keeps increasing ultimately building up more pressure in the engine which can result in a downshift.

The interplay between the line pressure, the primary regulator valve and the throttle position sensor, as well as the master control module, determines the shift points for your automatic transmission, especially under hard acceleration.

Have your engine checked because there is something going on.

Let’s look at just how your throttle works with a little history to start. About 30 years ago, a switch started in the auto industry. Slowly, as digital electronics became more and more robust, “drive-by-wire” began to replace mechanical linkages. Before “drive-by-wire,” a throttle system was fairly straightforward. The accelerator was linked to either the carburetion or fuel-injection system by a series of linkages. You pressed on the accelerator and the linkages opened up performance as more air entered the fuel system and as the transmission kick-down activated.

This changed with full “drive-by-wire.” Instead of relying on mechanical linkages, the system uses a series of sensors such as the throttle position sensor and control modules (essentially microcomputers) to maintain, increase or reduce your speed. The system monitors a series of voltages that whose basics are stored in non-volatile memory. In its monitoring, it watches for major differences between sensors and modules. If the range is too far out of whack, the car is placed into either a safety mode where the engine shuts down or limp-home where the engine and transmission go into second or third gear and remain there so that your car can move until you can get it to a service area.

If things get too far out of whack, the throttle control motor cuts in and physically moves things about until the engine shuts down.

So, you asked what I would recommend to be checked. The answer is relatively simple. Take an OBD-II reader, plug it in and look at throttle-specifid error codes, if they have accumulated. If they have accumulated, narrow down the problem and have it fixed. If, on the other hand, there are no codes for the specific problem, see if there are any codes relating to the fuel system as it may be that an outboard system is impacting the throttle.

In any event, the throttle system needs work.