Errors cleared after disconnecting the battery

Hello,
I have a general question. When the engine, for example, goes into a limp mode, a fault code is usually stored. If you disconnect the battery, will the error be automatically cleared, or will you still be able to read the error code after reconnecting the battery?

Thomas.

Hi Thomas,

It depends on the control unit and its wiring/power supply.
My engine control unit (ECU) in my AHF car is definitely completely disconnected from the power supply (battery) when I turn the ignition key to the 'off' position.
From MSTG, I only know that errors disappear after a certain number of x-motor starts and do not reappear.

Best regards, Rainer.

I'm familiar with that too; errors are automatically deleted after being restarted X times. But are you sure your MSTG is de-energized after you remove the key? What about the immobilizer then?

Thomas.

So, what about the immobilizer then?
Huh?

When the key is removed and the engine control unit (ECU) is without power, what should happen to the wireless key system (WFS)? Without voltage at the MSG (Main Service Ground), you don't need a WFS (Wireless Field System), so it can be de-energized.

Without voltage at the MSG (Main System Generator), you won't be able to start the engine, so you won't need any WFS (Water Fuel System) functionality either.

Or have I misunderstood your question?

-Private

Okay. Let's say it's a theft protection system. In case of a break-in, an alarm is triggered (horn, warning light, etc.). Wasn't this anti-theft feature integrated into the WFS (at least until recently)?

Uwe Ross probably wrote something about that topic once... -> Use the search function.

For example, if the engine goes into a limp mode, a fault code is usually stored. If you now disconnect the battery, will the error be automatically cleared, or is it still possible to read the error code after reconnecting the battery?

It depends on your engine control unit (ECU). If it's OBD-II or EOBD compatible, it's mandatory that the error codes are stored in a non-volatile memory (usually an EEPROM). This is the case for all ECUs in US models since the 1996 model year. And most ECUs in European models have the same hardware base, and I imagine they function similarly. I'm less certain about older control units.

-Uwe-

The EDC stores errors (including intermittent ones) as well as all relevant data in an EEPROM.
I intentionally triggered some errors, and all of them (though sporadically) were logged.

The EDC is also NOT connected to a constant power supply.

There are two power paths:
- via terminal 15 (ignition switch)
- about relay 109

At the latest when the machine starts rotating, the R109 is connected to the EDC. This provides power to the sensors, actuators, and their associated amplifiers. Furthermore, the EDC gains the ability to maintain its own power supply even AFTER the ignition is switched off (known as 'afterrun'). This makes it possible to monitor the engine's shutdown process (important, for example, for a quick restart) or to take into account special conditions (high temperature, coolant pump operation after shutdown, etc., activating shutdown devices).

As soon as the EDC disconnects itself (i.e., deactivates R109), it becomes completely and totally de-energized. Therefore, disconnecting the battery will not help in this situation.

CU Gremlin.