What to do if the EPC light on the dashboard lights up and how to fix it
What does the illuminated “EPC Light” symbol on the dashboard of VAG and Mercedes-Benz vehicles mean?
Any indicator that differs from the usual “add windshield washer fluid” and “low fuel” causes understandable concern in the car owner. It is doubly unpleasant when, with the appearance of an alarming symbol, the car begins to drive worse, or refuses to do so at all. Let’s figure out what the meaning of the “EPC Light” symbol on the dashboard, familiar to many owners of VAG and Mercedes-Benz cars, is.
What is EPC Light in a car
EPC is an electronic system for monitoring the engine power of a car. It is a set of electronically controlled components responsible for the engine power. Despite the more than extensive definition (there is also “Check engine”), EPC includes very specific units. First of all, it is a throttle unit, an electronic gas pedal that controls its operation, and a brake pedal sensor.
EPC stands for Electronic Power Control. It is installed, in particular, in Mercedes cars, models produced by Volkswagen Group: Skoda, Volkswagen, Audi and others.
EPC Error on Dashboard: 5 Reasons
Below are the main reasons for the EPC error to appear on the dashboard. It is worth remembering that, like the Check Engine symbol, the EPC indicator itself does not indicate any specific error. To accurately determine the malfunction, you will either need to contact a service station or have your own OBD-II diagnostic scanner.
1. Power failure
The EPC error that occurs often indicates not a real malfunction, but problems with the power supply of electronics. For example, if there is poor contact between the battery terminals or the signal is floating in one of the connectors – for example, the throttle or gas pedal. Also, Mercedes owners often report a connection between the EPC indicator and a low battery charge.
2. Malfunction in the throttle assembly
Among other electronic components, the throttle includes a throttle position sensor (TPS). This sensor determines the opening angle of the throttle depending on the pedal pressure and engine operating mode. If the TPS is already significantly worn out, but partially works, the EPC error will only occur at a certain position of the gas pedal. For Skoda, Volkswagen, Audi and other brands of the VAG group, if the EPC lights up at idle, but goes out when the revs are increased, this most likely indicates a malfunction of the throttle assembly. If the position sensor has completely failed, or another component (for example, a servo drive) has failed, the EPC will be constantly lit.
3. Malfunction of the gas pedal
Here the situation is similar to that in the throttle assembly. The degree of pressing of the electronic gas pedal is determined by the position sensor located in it. If it is worn out or completely out of order, the EPC symbol on the instrument panel will either appear periodically or light up constantly.
4. Brake pedal malfunction
And again, the most common cause is the position sensor. If it is “stuck” or gives an incorrect signal, the control unit thinks that the car is slowing down. Consequently, it completely stops supplying fuel. A conflict arises: the driver presses the gas, and the brake pedal sensor gives information that it is necessary to stop. The result is an EPC error and a transition to emergency mode with forced traction limitation.
5. Throttle adaptation is required
An electronic throttle valve requires initial calibration to work correctly, which determines its minimum and maximum opening positions. For new cars, such adaptation is performed at the factory, but for a number of reasons it can “fly off”, as a result of which the owner observes an EPC error on the dashboard. The reasons may be different, among the main ones are disconnection of the throttle electrical connector and mechanical impact on the valve. Both are almost always the result of the throttle valve cleaning procedure.
How to fix EPC error
Here, everything depends on the owner’s experience and knowledge. But the decisive role is played by the fact that there is a diagnostic scanner to identify the fault code – after all, the EPC icon will not tell you anything specific. By connecting the device via the OBD-II protocol (supported by all modern cars), you can immediately understand in which direction to continue further diagnostics. Below are examples of diagnostic codes related to the EPC error on VAG cars, with decoding and some comments.
P1171 – Throttle Position Sensor 2 Signal Invalid
P1172 – TPS 2 signal too low (short to ground)
P1173 – TPS 2 signal too high
P1335 – Torque control not possible (here, with a high degree of probability, we can talk about the failure of one of the sensors responsible for calculating the fuel supply)
P1388 – Control unit malfunction
P1542 – Invalid TPS 1 Signal
P1543 – TPS 1 signal too low
P1544 – TPS 1 signal too high
P1545 – Throttle servo failure (either actual fault, poor connector contact, or open circuit in wiring)
P1559, P1579 – Throttle re-adaptation required (electronics cannot find zero position point)
P1564 – Insufficient voltage when attempting to perform basic setup (high probability TPS failure)
P1568 – Servo Motor Mechanical Malfunction
P1630 – Low Signal Accelerator Pedal Sensor 1
P1631 – High Signal Accelerator Pedal Sensor 1
P1633 – Low Signal Accelerator Pedal Sensor 2
P1634 – High Signal Accelerator Pedal Sensor 2
P1677 – EPC indicator lamp circuit is permanently shorted to positive (there is no actual fault, the error indicates a short in the EPC indicator itself)
If we do not take into account the simplest scenarios, with obvious damage to the wiring or poor contact of the connectors, then to fix the malfunction, the average car owner will need to contact the service.
Is it safe to drive with EPC on?
Formally, an EPC error on the instrument panel is not a prescription for a complete stop of movement. However, in parallel with the appearance of this symbol, a corresponding warning is displayed on the information screen. It usually recommends an immediate visit to a service station, and also informs that the engine speed will be forcibly limited until the fault is eliminated.
It is worth paying attention to an important point: even in the obvious absence of symptoms of a malfunction (the car drives as usual), it is not worth driving for a long time with an EPC error. Firstly, the normal, at first glance, behavior of the car does not mean that the engine management system is operating in the normal mode. A modern engine has many mutually complementary control and management systems.
Each of them, if one of the components of the “neighbor” breaks down, can often partially compensate for its functions. But, in any case, this will lead to excessive fuel consumption, reduced traction, increased contamination of the piston group with coke. In other words, it is definitely not good for the engine, and disadvantageous for the owner.
Finally, there is a real accident factor in the EPC indicator. If the error is floating and occurs spontaneously, simultaneously limiting the power reserve, this can be extremely dangerous. For example, when overtaking, when the driver began a maneuver without errors on the dashboard, and in the process the EPC suddenly lit up and the power dropped sharply. Therefore, when such an indicator appears, it is better not to delay visiting a professional service station.
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